History Main / BonusBoss

** Both [[VideoGame/RatchetAndClankGoingCommando second]] and [[VideoGame/RatchetAndClankUpYourArsenal third]] game of original trilogy have these in [[MonsterArena Gladiator Arena Challenges]]. The second has four: the first arena includes Chainblade and B2-Brawler -- the latter is pretty difficult to beat when you first enter Maktar Resort. The second arena has Arachnoid and Megapede. The third game has only one dual-bonus boss, Terrible Two -- the second boss, Scorpio, has to be fought later in the game. These bosses appear as separate challenges, challenges with some kind of limitation ([[NoDamageRun taking no damage]], weapons switching on its own ...) and usually take part in ultimate challenge consisting of many rounds.

** ''VideoGame/MortalKombat2'' continued the tradition with Noob Saibot, Jade, and Smoke. Noob Saibot appears only if you win 50 battles consecutively. Jade appears if, on the fight before the question-mark box, you only use the Low Kick button to defeat your opponent (can be done on any round). Smoke is the most difficult to get, as you have to make Dan Forden appear and say "TOASTY!" while fighting on the Portal stage, then hit Down + Start while he's on the screen.

** ''VideoGame/SNKVsCapcomSVCChaos'' has Princess Athena and Red Arremer.

* ''VideoGame/TheLegendOfSpyro: Dawn of the Dragon'' has Elite Enemies in every chapter. They look like [[PaletteSwap normal enemies with a few modifications.]] [[BossInMookClothing They're not.]] They're hard to ''damage,'' let alone kill...

** ''VideoGame/MegaManX6'' has some bonus bosses by going through alternate routes to fight Zero Nightmare, which unlocks Zero, and High Max, which lets you skip straight to the last areas of the game; it's hard to find out [[GuideDangIt how the hell you're supposed to even damage him]]. Going to the secret areas again will let you fight Dynamo, which lets you get large amounts of souls.
** ''[[VideoGame/MegaManX8 X8]]'' has Cut Man, again. You need to go through Optic Sunflower's stage to reach a 3D-ified version of where you fought him in Mega Man.
** ''[[VideoGame/MegaManX3 X3]]'' has Vile MK-2, which does nothing when defeated, except when his weakness (Ray Splasher or Spinning Blade) is used to score the final hit, in which case you won't fight him later. This is only the first step in getting the InfinityPlusOneSword. The player will then fight Mosquitus in the final stages instead - defeating it with Zero is the requirement for X to obtain the Z-Saber. There is also Bit and Byte, whom you can find and battle in hidden areas in stages. If you beat them using their weaknesses to score the final hit (Frost Shield or Triad Thunder for Bit and Tornado Fang or Ray Splasher for Byte), then they will be replaced in the final stage by Press Disposer. If even one of them is left alive, however, then the player will fight Godkarmachine O Inary in the final stages.
** ''[[VideoGame/MegaManX2 X2]]'' has the X-Hunters, Serges, Violen, and Agile, who can be encountered in hidden areas in stages. If you beat them at the first opportunity, you receive parts of Zero, and collecting all of them enables you to skip the fight with Zero in the final stage. You still fight the X-Hunters in the final stages, regardless of whether you fought them before or not, though.
** In ''VideoGame/MegaManZero3'', in a secret area in the second-to-last level that can only be opened by going into {{cyberspace}}, Zero will encounter Phantom, who died two games earlier, ready to fight him to [[SecretTestOfCharacter test his worth as a hero]]. Victory will net the player the [[InfinityPlusOneSword infinity plus one, er, boots]].

* ''VideoGame/IttleDew'' has one at the end of the [[BonusDungeon Master Cave]]. Oddly, it's the one boss you beat through brute force rather than [[PuzzleBoss some kind of puzzle]].

* The Smokey Progg in ''VideoGame/{{Pikmin}}'' is one of these, as you have to go out of your way to find it (and do so before the end of Day 15, [[PermanentlyMissableContent or else it'll disappear forever]]) and it drops an object that produces 100 Pikmin when it dies. It has the difficulty to match as well: just touching its slime trail can kill several Pikmin at once, and any Pikmin attacking the Progg will probably be thrown right into it.
** ''Pikmin 3 [[UpdatedRerelease Deluxe]]'' features a new boss at the end of the "Olimar's Comeback" sidestory: [[spoiler: a golden mix between a Shaggy Long Legs and the otherwise-absent Raging Long Legs from ''Pikmin 2''.]] Since it's not part of the main game, it lacks a Piklopedia entry and thus goes unnamed.

** In ''VideoGame/TouhouKouryuudouUnconnectedMarketeers'' Chimata has been beaten, but the Rainbow Dragon Cave has not been fully explored and Megumu has sent out Tsukasa to fight with Misumaru upon learning about their existence and deeming them a mine looter. Using a special Ability Card that grants them the ability to breathe in anoxic enviroments, the protagonists brave the Rainbow Dragon Cave once again and face Momoyo Himemushi, an ''oomukude'' and supplier of dragon gems for Megumu, making the whole Ability Card scheme possible in the first place.

[[folder:Role-Playing Games]]
* In ''VideoGame/AlphaProtocol'', the BloodKnight ActionGirl SIE will offer to team up with you during the mission where you first encounter her. You can agree to the alliance, or you can attack her (or you can agree, complete the mission, then attack her when you encounter her again at the end of the mission). Not only will she not die when you win, but [[RelationshipValues your rep with her]] will increase.
* ''VideoGame/AngryBirdsEpic'' has two:
** The more obvious one comes after getting the submarine. Tapping on the whirlpool takes you to the level "Maelstrom" where you can battle the Poseidon Pig, who has more health than the FinalBoss.
** There’s also the "Mouth Pool" level, a ten-phase wave battle against a Necromancer Pig who summons virtually every undead pig in the game. It’s only on the tenth wave that the Necromancer Pig fights you directly.
* ''VideoGame/{{Atelier}}'':
** The 3 Golden Pigs at the end of the BonusDungeon (Mull's Dungeon) in ''VideoGame/AtelierIrisEternalMana'', which are significantly more difficult than the final boss.
** In ''VideoGame/{{Atelier Iris 2|The Azoth of Destiny}}'', the fights at the Dragon's Nest, particularly the last one against 3 Instant Brownies. However, while they are more powerful than the last boss, the overly-easy battle system makes them no more difficult than anything else, provided the player has stocked up on resurrection items.
* The ''Franchise/BaldursGate'' series:
** Aec'Letec in the ''VideoGame/BaldursGateTalesOfTheSwordCoast''. He's more of a FinalBoss to the expansion pack; said expansion pack is an optional sidetrack from the main story, he can be safely skipped after finishing Durlag's Tower and is much worse than the game's actual final boss.
** Kangaxx in ''VideoGame/BaldursGateII'', who could only be hit by +4 weapons, and, in his demilich form, could cast the annoying insta-kill spell Imprisonment at will, which had the tendency to mess up romances if your love interest got hit. Kangaxx does have an AchillesHeel, however, in the form of a [[WeaksauceWeakness shockingly poor]] [[OneHitKill death save]] for his level.
** Most of the dragons in the game are also optional fights, though they give some good rewards after being slain.
** There's also an optional (and completely story-irrelevant) fight against some demon knights in the Underdark.
** In the expansion pack ''VideoGame/BaldursGateIIThroneOfBhaal'', the Bonus Boss was Demogorgon, an incredibly powerful demon imprisoned at [[BonusDungeon the bottom of Watcher's Keep]].
** The Twisted Rune is an order of evil spellcasters who, when you enter their lair, assume that you've come to foil their plans and attack you. They're sensibly skeptical if you claim to have found them by accident, because the only way that would happen is if you were wandering around a bad part of town while carrying an incredibly rare and valuable type of gemstone and opening doors at random. (This is in likely exactly what happened, unless you looked at a guide. The clues that would lead you to them were never put into the game.)
* ''VideoGame/BahamutLagoon'' has special "side quests" -- essentially single battles -- available throughout the game. One of them, appropriately named Hard Dungeon, is only available in the last seven chapters and is far more difficult than the final boss.
* ''VideoGame/BarkleyShutUpAndJamGaiden'' has a few:
** The spirit of Dikembe Mutombo is the boss of a bonus dungeon and gives Barkley the Holy Dunk attack.
** A duergar [[spoiler:(actually Balthios, who is a Wereduergar)]] can be fought if you take the ferry to Liberty Island instead of the Underground Railroad.
** The Ghastly Darklord is encountered by checking a seemingly empty corner in Proto Neo New York.
** Kevin Garnett is the final opponent in the Arena in the optional [[AnotherDimension B-Ball Dimension]].
* ''VideoGame/BatenKaitos Origins'' gives us a few. There's [[spoiler:Nasca, Valara, Heughes, and Wiseman]], who are fought to tie up loose ends; one of them allows access to the game's TrueFinalBoss. There's also Arma Prototype M, a.k.a. The Wicked Gawd, who is the final boss of the Coliseum and is ''absurdly'' hard.
* The UsefulNotes/Xbox360 game ''VideoGame/BlueDragon'' has several Dragons that don't ''need'' to be beaten, but give the player a useful accessory if they are. Genuine Bonus Bosses include the Gold Mecha Robo, the King Poo, and the Golden Poo.
* Kisuke in ''Manga/{{Bleach}}: Soul Carnival 2.'' The thing with him, though, is that he can be fought pretty early on in the game, not that you'd have any chance of survival then. Until you clear the Soul Society missions, he'll probably kill you with just one combo. And he has two supports, whereas most bosses only have one, '''OR''' the fact that his Burning Attack can even hit you if you're off-screen, and it stuns you invariably (as Burning Attacks never miss). When you defeat him, you'll unlock him as a playable character.
* ''VideoGame/{{Bloodborne}}'', naturally being a SpiritualSuccessor of ''Dark Souls'' as listed above, has even ''more'' optional boss encounters than ''Dark Souls'' does, owing to the fact you're actively hunting out these horrors than reacting to their mandatory discovery like in ''Dark Souls'' -- and make no mistake, these include more than a few nasty surprises lurking within the depths of Yharnam that don't have to be beaten in order to win the game, but doing so anyways nets new content, areas and locations:
** The Cleric Beast is a boss that doesn't have to be fought in order to win the game, yet he's very commonly the first boss many players fight by virtue of gating off exploring more of Yharnam, and he [[EstablishingSeriesMoment establishes the de facto nature of the game]] by being ''very'' aggressive unlike almost any other boss in ''Dark Souls'', and actively punishing tactics of turtling by forcing you to be constantly on the offensive while dodging each of the Cleric Beast's attacks. For many players, it serves as a WarmUpBoss and in many ways equivalent to ''VideoGame/DarkSoulsIII'''s own Iudex Gundyr for being the "tutorial" boss.
** The Blood-Starved Beast is encountered in the dead-end segment of the Church of the Good Chalice, and he is ''ridiculously'' aggressive and hard-damaging, while also boasting poison damage and rapid-fire attacks that'll leave most players dead before they can even react. The way in order to quickly defeat this boss is to either be even more aggressive than it while reading its tells, or simply [[spoiler:[[OutsideTheBoxTactic using Pungent Blood Cocktails]] to lure the Beast away from you and to the location where you tossed it]]. Given how aggressive the boss is, you'll likely need every advantage you can get.
** The Old Hunters DLC adds four new super-bosses to the game, all of which are varying assortments of pure ''nasty''. How nasty, you may ask? Nasty enough that for every single boss according to [=PlayStation=] 4 Trophy data, ''[[HarderThanHard less than 40% of every single boss in the game was actually completed against]]'', with the vast majority being fights that most people just gave up against or skipped entirely. To name them in order of appearance assuming HundredPercentCompletion:
*** The first mandatory encounter is Ludwig, the Accursed, [[WasOnceAMan who was once a proud hunter that sadly became a horrific horse-like monstrosity]]. The fight immediately has the DLC go for the jugular with highly-damaging and outright ''aggressive'' attacks that'll very likely two-shot if not ''[[OneHitKill one-shot]]'' you, and being very hard to get a read in on without being punished by the absolutely frantic pace of the fight comes at. Even worse, just when you think the second phase is going to be merely a more aggrssive version of the first fight, [[spoiler:Ludwig regains his sanity and becomes Ludwig, [[RedBaron the Holy Sword]], and promptly equips itself with From Software's trademark [[RecurringElement Moonlight Greatsword]], which changes the fight from a fight against a crazed beast to the dignified slashes of a MasterSwordsman, and the fight as a whole ''will'' wreck your face in if you don't change tempo immediately]].
*** The next boss is Laurence, the First Vicar, which is basically the unholy fusion of the Cleric Beast and Vicar Amelia on steroids, and also ''[[ManOnFire on fire]].'' He immediately gets ridiculously aggressive and very hard to dodge with a frenetic and frantic combat pace throughout the entire fight that ''will'' smash your face in if you don't come with lots of preparation, whom even then will probably kick your ass. This is because on top of a wild first phase, the second phase has Laurence [[TurnsRed Turn Red]] and lose his legs, which makes him even ''more'' dangerous as he begins spewing fire everywhere and potentially one-shotting you while he rampages around the place. It really ought to be telling that in a DLC that's already optional to beat the game over and serves to test your challenge, Laurence is the only boss in the entire DLC who ''isn't'' mandatory to fight, giving it a double dosage in being a royal pain in the ass that is only to be beaten for a BraggingRightsReward.
*** The second mandatory boss in the DLC is Lady Maria of the Astral Clocktower, who is unique in being one of the only purely-human bossfights in the game, aside from [[spoiler:Gehrman, the First Hunter]] and [[OurWerewolvesAreDifferent technically]] Gascoigne, and yet ''still'' manages to be ridiculously hard. On top of [[FlashStep Flash Stepping]] everywhere to the point of teleport spam, she is also ludicrously fast and will likely cut your Hunter to ribbons before they could even react. The second phase of the fight is even worse, as she ends up ''slashing herself to use a blood blade that is set on'' '''''fire''''', and she uses it in reckless abandon in a last-ditch attempt to stop you. What makes this even more interesting is that the lore of the fight reveals [[spoiler:Maria always hated blood weapons, something confirmed by the description of the Rakuyo; given [[TheseAreThingsManWasNotMeantToKnow what she's guarding]] and her involvement in the atrocities that occured in the Fishing Village, it's very understandable that [[BatmanGrabsAGun she resorts to using the very things she hates]], [[GodzillaThreshold just to stop you from reaching the Fishing Village]]]].
*** The FinalBoss of the DLC and arguably the TrueFinalBoss of the entire game is regarded by many players as one of the hardest bossfights, if not '''''the''''' hardest bossfight, [=FromSoft=] has ever put out in [[VideoGame/DemonsSouls any]] [[VideoGame/DarkSouls of]] [[VideoGame/{{Bloodborne}} its]] SoulsLikeRPG games. How hard, you may ask? Hard enough to put every single boss in the ''entire game'' and on this list (and hell, most bosses on ''this very page'') to ''shame.'' It is none other than the [[spoiler:Orphan of Kos, the child of the deceased Great One Kos]], whom promptly proceeds to prove to be ''vicious.'' It is ''extremely'' aggressive beyond what should be possible for an already-aggressive game like ''Bloodborne'', extremely hard to read tells to dodge its attacks, and is both [[LightningBruiser faster, stronger and more durable than you will ever be]]. Combine that with the bossfight being in many ways a MirrorBoss with [[spoiler:the Orphan using its, ahem, [[DoesThisRemindYouOfAnything placenta-like organ]]]] as a Trick Weapon as they ''very'' quickly began swarming against you with an absolute slew of aggressive attacks that get even ''worse'' on the second phase; it's aggressive enough that ''[[ReadingsAreOffTheScale even in a game with aggressive combat in mind]]'', it's the ''one'' boss that is completely impossible to control through aggression alone, resulting in many, ''many'' player deaths just to kill this thing, with a non-insignificant number of these players giving up outright. Given the fact that [[spoiler:the Orphan of Kos is merely a ''baby'' Great One, and is even more dangerous than any other Great One boss in the entire game by a mile, is it any wonder why the Hunters were so desperate to keep it contained to the Fishing Village?]]
** Among the optional Chalice Dungeons is also a massive amount of optional bosses, from the Amygdala, to the Bloodletting Beast, to the Maneater Boar, to the Watchdog of the Old Lords, all of which are more than capable of ruining the day of any traverser of these underground, optional randomly-generated dungeon treks. Special mention explicitly goes to the Watchdog of the Old Lords, as they're both on fire like Laurence is, ''and'' is most likely fought in a dungeon that cuts your total HP count in '''half''', with most of its attacks very often being one-hit kills given the level you're required to fight it at, making for an infuriatingly difficult boss trek.
* ''VideoGame/BoxxyQuestTheGatheringStorm'' has at least eighteen of them, and possibly as many as ''twenty-five'', depending on whether you consider the Sky Abyss bosses to be ‘bonus’ or not.
** Pale Luna, the [[VoluntaryShapeshifting Phisher King]], the [[CreepyDoll Fetish Dolls]], Trahald Prime, the [[ChestMonster Hateful Reliquary]], and the Soul of [=TORment=] - all related to the Deep Web BonusDungeon.
** ORDERHEAD, Goddess-Slayer Forby, the Hydra, and the [[{{Santabomination}} Spirit of CTH’RISTMAS]] -- appear at the end of various minor sidequests.
** Lady Ny’agai and the [[DanceBattler Funky Infoshade]] -- just kind of standing around at the end of side paths, waiting for you to find them.
** [[GlitchEntity not_intended/Nihilerror]] and [[spoiler:Esoteraphim]] - deeply hidden with GuideDangIt requirements, and two of the most challenging fights in the game.
** The three entities labelled “?,” all related to [[BigBoosHaunt /x/]] in some way.
** The Overtaken Dragon, which is encountered along the main path in the final dungeon, but can be skipped by simply [[TreacherousCheckpoint not interacting with a certain save point]].
** The Sky Abyss contains the Nova Proxy, Echo of Legion, Echo of Virtua, Ascended Oversight, [[spoiler:Cracky the Sky Queen]], [[spoiler:STORM Boxxyfan]], and the [[spoiler:[[TrueFinalBoss Legion Singularity]]]]. Fighting them isn’t necessary to beat the game, but it’s what leads to the [[GoldenEnding best ending.]]
* A staple of Zeboyd Games: the Dragonduck in ''VideoGame/BreathOfDeathVII'', DEM, SARA and Soulcaster in ''VideoGame/CthulhuSavesTheWorld'', and DEM, Lita, Cthulhu and T in ''VideoGame/CosmicStarHeroine''.
* ''VideoGame/BreathOfFireIII'' had the Berserker, difficult because it attacked for three to four hundred damage, and often attacked several times before any of your characters got to. Worse, it was a [[BossInMookClothing random encounter]] on the way to getting one of your dragon genes, and was a normal monster.
** And in the same area was an even tougher Bonus Boss, the Arch Mage. He has far less HP than Berserker (only about 3,000 compared to the Berserker's 15,000), but regenerates 1,500 of it every single round, which is more than most casual players can deal in a single round, and is capable of hitting just has hard as Berserker. In fact, if you have one living and two dead characters, Arch Mage will USE A SKILL THAT REVIVES THE TWO CHARACTERS. Presumably, he does this simply as a means of embarrassing you further.
* ''VideoGame/BreathOfFireIV'' has Rider as a hellish random encounter in Mukto. With 40,000 HP he is already a tough opponent but he also regenerates 20,000 HP every turn...try to overcome that.
* ''VideoGame/BreathOfFireDragonQuarter'' had Dover, who was the final boss in the BonusDungeon. As long as you have a high enough level (around 50), he's not that bad. The only problem is is that his defense switches from regular ol' attacks to Dragon defense. So your time limit is based on how much you have left on the D-Counter. [[SpellMyNameWithAnS Lin's/Rin's]] "Shatter!" technique is particularly effective here.
* ''VideoGame/BugFables'': There are five Bounty Bosses you can take from side quests that are a major step up in difficulty compared to the storyline bosses. There is also the Mother Chomper, encountered in an optional dungeon, the Broodmother in the power plant, multiple criminals and hostile bugs fought in sidequests, and a fight against Team Maki in the Playable Epilogue as the final challenge in the game. Patch 1.1 adds a fight against Team Slacker, who are even more powerful than Team Maki.
* ''Byteria Saga: Heroine Iysayana'' has a BonusDungeon you cannot enter until you have finished the main quest, with three bosses inside: [[spoiler:Rematches with Vile and Caryneth, and ultimately Lord Sick, one of the archvillains from ''Byteria Heroes''. That series got a ContinuityReboot around the time ''Heroine Iysayana'' was finished and didn't become available in English at all until later, making it something of an EarlyBirdCameo.]]
* ''VideoGame/ChronoTrigger DS'':
** The game has an Alternate Final Boss, the Dream Devourer, which has ties to the final boss of ''VideoGame/ChronoCross'', the Time Devourer. It is unlocked after you clear all three of the {{Bonus Dungeon}}s that appear after you defeat the normal FinalBoss.
** Before that, there's the [[BonusDungeon Dimensional Vortex]] fights against the Alabaster Shade, Crimson Shade, Steel Shade, and [[spoiler:Once-King Dalton.]]
** The [[BonusDungeon Lost Sanctum]] also has some, like the multiple fights with the Nu Guardian.
** The ultimate form of Spekkio is also one of the strongest bosses in the game. But since you need maxed out characters to even challenge him there is not much strategy involved anymore...
* ''VideoGame/CorruptionOfLaetitia'': When fighting the Predatory Birds in the map north of Gruhnwald, there's a chance that [[spoiler:Hawkzombie]] will show up in the second turn to fight the party.
* ''VideoGame/DarkSoulsI'' is absolutely swarming with these guys; due to the open-ended nature of the series, it's very possible to skip a large cut of the bosses in the game just to only finish the mandatory bosses to "win" the game. [[HarderThanHard And you should be very thankful for that, a lot of the time]]. To wit:
** [[NamesToRunAwayFrom The Hellkite Dragon]] that guards the bridge between the Undead Burg and Undead Parish is more of an obstacle than an actual boss, but players have naturally decided to try to kill him regardless. If you do decide to try to kill him, you have to continually dodge that 1 hit kill fire breath of his and bait him to land on the bridge to actually deal damage. Forget ranged attacks: at lower than 50% health, he starts ''regenerating'' at a rate that will almost certainly outpace your ranged attacks, and is tough to overcome even with melee. However, you don't even get anything other than 10,000 souls for killing him, which, at the level you're likely to be at if you do kill him, isn't all that much. So killing this dragon really just ends up being for bragging rights.
** The game has several in the optional areas of the game. The first one most players see is the Stray Demon, a much stronger version of the tutorial's Asylum Demon that drops a highly valuable Titanite Slab. Others include the magical Moonlight Butterfly in Darkroot Garden, the illusionist Dark Sun Gwyndolin in his father's tomb, and the half-Dragon Priscilla in [[BonusLevel the Painted World.]] Priscilla is a little bit more optional tham usual because she won't attack until the player does first, and her dialogue points out that you can exit the boss arena and pass through the Painted World without a fight. The difficulty of these encounters depends on the player's progress through the game and they are much easier than the final boss, but they still provide a unique challenge to those who look for them.
** The DownloadableContent ''Artorias of the Abyss'' adds a new hidden BonusLevel with several bosses in it, all of them difficult fights. The bonus content even has its own bonus boss; while most of the bosses block off new bonfires and are normally accessible, the black dragon Kalameet is unlocked by a side quest and only gives the [[BraggingRightsReward Calamity Ring as a reward, which double all damage taken.]] Cutting off his tail creates a powerful weapon, but doing that is even harder than killing him. Adventurous players can also find a fight against two of the first [=DLC=] bonus boss at the same time.
* ''VideoGame/DarkSoulsII'' has several:
** The Ancient Dragon is a brutal MarathonBoss with a lot of health and all of its attacks can kill you in one hit unless you have extremely high Fire resistance. The saving grace is that most of its attacks are fairly telegraphed and can thus be avoided rather easily. Except when it decides to fly up and rain fire on the arena. Avoiding that can be a struggle. Upon defeat, it drops an item that makes the next Bonus Boss easier.
** [[spoiler:King Vendrick]] is an AnticlimaxBoss whose attacks are slow and easy to dodge, though he can kill you in one hit if you aren't careful. However, he is also a PuzzleBoss since his defense is incredibly high, making him impossible to defeat if you don't have [[spoiler:Giant Souls]] in your inventory. Upon defeat he drops nothing. [[spoiler:The rewards appear behind a hidden locked door in a different area.]]
** The Darklurker is the most obscure. The previous two are at least encountered in the storyline. It is entirely possible to never encounter this boss [[GuideDangIt if you aren't playing with a guide]]. You need to discover and join an hidden covenant and fight through three small dungeons filled with dangerous black phantoms just to meet the Darklurker. Your efforts are "rewarded" with a harrowing battle against an eerie angelic figure who hurls powerful pyromancies, hexes, and sorceries at you while flying around the arena. It [[SquishyWizard thankfully has much lower health]] than the other two bonus bosses. Upon defeat, it drops its soul which can be traded for a powerful hex. Its defeat also maxes out devotion to the hidden covenant, which comes with its own rewards.
** Also notable are the DLC challenge areas, four NintendoHard optional paths designed for co-op. All of them have appropriate bosses at the end, though all except [[spoiler: Sir Alonne in the Memory of the Old Iron King]] are Invader type enemies or palette swaps.
** You need four [[PlotCoupons Great Souls]] to reach Drangleic Castle, and there are four bosses with Great Souls. However, you can kill one boss, take their Great Soul, use a Bonfire Ascetic to resurrect that boss, then kill them again and take a whole new Great Soul again. Repeat ad nauseum and almost every boss in the game before Drangleic Castle is Bonus.
** Raime the Fume Knight from the ''Crown of the Old Iron King'' DLC is one of the toughest bosses within the entire game. It's telling when you find messages outside his fog wall commenting on misery and sadness ahead, because he's statistically the boss with the highest failure rate in the game. Most of his attacks come in hard and fast with his straight sword, but then occasionally he'll swing his ultra greatsword and either shave off a massive chunk of your life or utterly ruin your stamina. After he's lost about a third of his HP, [[TurnsRed he gets serious]], buffs his ultra greatsword with a dark flame and gains a new, significantly more aggressive move-set that punishes players that either can't time their dodge right or just stand there expecting to block his strikes. Additionally, if you haven't collected the Smelter Wedges throughout the DLC, Nadalia's idols will keep healing him if he's near them, and if you have Veldstadt's helm equipped, Raime will immediately enter his second phase move-set without you hitting the HP threshold.
* ''VideoGame/DarkSoulsIII'' ups the ante with the Nameless King, who is considered one of the toughest direct fights in the entire series. First you fight him on his Storm Drake, the King of Storms, who is so large that [[CameraScrew locking onto him makes it near impossible to see the Nameless King's attacks from above,]] combined with a particularly difficult to avoid fire attack from above you can only evade if you start running the ''instant'' the Drake starts flying overhead. Once the Nameless King is on-foot, however, it only gets [[UpToEleven harder;]] put the moveset of Ornstein with a super adrenaline boost on a [[PhysicalGod God of War]] that is hyper-aggressive, extremely mobile, and can kill even the sturdiest of builds in a handful of blows, and pair this with fighting on a moving cloud background that hinders depth perception. It's not uncommon to see 85% of the fight, at minimum, being spent ''rolling for dear life.''
** It's also possible to beat the game without even realising that you can cut the rope bridge in the Catacombs of Carthus to turn it into a ladder to Smouldering Lake, so you end up missing the MiniBoss battles against the Fire Demon and Carthus Sandworm, plus the battle against the Old Demon King.
** None of the DLC has to be completed to win the game, meaning that [[spoiler:Sister Friede]], Halflight, Spear of the Church, the Demon in Pain and Demon from Below, and [[spoiler:Slave Knight Gael]] are somewhat optional, but you can finish the main story of ''Ashes of Ariandel'' without finding out that the area the Champion's Gravetender and Gravetender's Greatwolf fight is in even exists, let alone getting to it, and Midir's boss arena in ''The Ringed City'' requires you to defeat him on a bridge and then figure out where the hell his proper arena is.
* ''VideoGame/TheDenpaMen'':
** The first game has two. One mid-game dungeon appears to have two bosses -- a Water-type Golem and an Ice-type Golem. The Ice-type Golem is [[PathOfMostResistance more difficult to get to, and is the true boss of the dungeon.]] The Water-type Golem, however, gives you a few extra goodies if you beat it. At the very end of the game, you can also choose to fight [[spoiler: The True King, the final form of the King of Evil. He has his own RareRandomDrop, and each time you defeat him, he drops an emblem that can be sold for a [[VendorTrash tidy sum of money]].]]
** The sequel has ''even more'' of these, most of whom are based around chess pieces. Each of the four [[BonusDungeon Caves of Darkness]] contains a different variation on the Knight, and each one is progressively more difficult -- especially because the Caves are [[TimedMission timed,]] and even though you can keep battling if you run out of time, if you do, you'll be kicked out of the dungeon before you can collect your rewards for completing it. There's also a Pawn who you have one required fight against early on--but he keeps getting stronger and stronger throughout the game, and you can return to challenge him after different story events. [[spoiler: The last two sets are linked -- the "big" BonusDungeon ends with a fight against the Demon Queen, who serves as a combination of this and a TrueFinalBoss. ''This'' unlocks the Bishop, King, and Queen, who fight you back to back in a CallBack to the original game's final boss.]]
* After beating Machinedramon and finishing the main story in ''VideoGame/DigimonWorld'', you can continue the story and find a new level with high powered {{Mook}} Digimon. At the end is Machinedramon once again, only this time his health is maxed out at 9999 and his stats are also quite high. This is all for bragging rights.
* ''VideoGame/DragaliaLost'' has quite a few of these in the Advanced Dragon Trials starting with clearing Chapter 6 in the main story. They are the highest forms of the Greatwyrms that Euden had recruited through the first five chapters of the game who are now testing to see if he's worthy of wielding their true power. Each one starts with a screen filling attack which will kill you in one hit unless you're sufficiently prepared for it. The Agito Invasion involves a new strain of bonus boss in that they're not only humanoid, but they have their own motives for why they do what they do. On Expert, bringing them down once has them transform into a bestial OneWingedAngel form that makes the fight mechanics change, the music get more intense and adds in a Break bar. Defeating them is what allows you to make the game's InfinityPlusOneSword weapons which are 6* weapons.
** [[BlowYouAway High Midgardsormr]] is the first one with attacks that involve [[SpinAttack spin attacks]], wind balls and an 8 direction attack that's a one-hit kill. The next attack involves a pillar attack that, once locked onto someone, requires everyone to group up together to mitigate the damage or the target gets killed in one shot. At the two minute mark, he unleashes tornadoes that will go left to right or right to left depending on which one is marked.
** [[PlayingWithFire High Brunhilda]] is the second one with fire breath attacks, claw swipes, and dive bomb attacks. She shoots out fireballs that leave volcanoes on the ground that are used to hide from her Hellfire attack that can deal big damage to the party. She also has a pillar attack that has to have everyone grouped up together to mitigate the damage or the target dies. Finally she does Grand Muspelheim that leaves a large chunk of the map on fire, allowing only ranged units able to hit her before doing another pillar attack. As she's close to defeat, she does Grand X-Muspelheim which now does an x-shaped pattern on the map.
** [[MakingASplash High Mercury]] is only slightly easier in that melee units won't need a wyrmprint to tank her first attack, though she has plenty of one hit kills up her sleeve with a 180 degree tail swipe, bubble blast and whirlpools. Four bubbles are then summoned that will allow each member of the party to get into to survive the waterfall attack, but if another member occupies the same bubble, it pops, meaning someone is going to die. After getting past that, she traps a random member in a water cage which has to be freed, then sends a homing bubble at another random member which has to be led away or they or someone else will die. After that, she goes to the middle of the room and conjures up a bubble storm that splits into more bubbles if they're attacked. Another waterfall will happen, but fiends will appear to try and burst the bubbles. Once the pattern is done, the trick is more that it's a damage race due to how high her HP is.
** While not one of the High Dragons, the Mercurial Gauntlet adds Fafnir Roy III who's meant to challenge only the best compositions of each element party. It starts off simple enough, but once an element hits 20 is when things start getting challenging. Getting each element to 40 is a very high risk high reward deal as it gives out rupies, mana, eldwater and for every 25 levels, Twinkling Sand which is used to make [[InfinityPlusOneSword tier five rank 2 and 3 weapons]]. After level 50, while the time limit becomes higher, his attacks become unavoidable and need to be healed through, turn to dragon before he attacks or bring him down before you wipe.
** [[PoisonousPerson Volk]] is the first of the Agito who has an utter hatred of anyone of privilege whether they use it for good or evil and will see them dead. His mechanics involve hitting the party with Plague which reduces resistances while he sends out flying disks around the arena. Underdog's Scheme sends out four gas clouds, two each having stun and sleep clouds that supercharges anyone who runs into it, otherwise it causes massive [=AoE=] damage, if not leading to a wipe.
* ''Franchise/DragonAge'':
** ''VideoGame/DragonAgeOrigins'' has several optional bosses among its many sidequests. The Revenants are powerful undead warriors that are managable on their own but get downright nasty with backup such as the ones that drop the Juggernaut equipment. Gaxkang the Unbound is an homage to Kangaxx from ''VideoGame/BaldursGate''. [[spoiler:Flemeth]] shapeshifts into a High Dragon. An actual High Dragon (who ''could'' be beaten easily if you surrounded it with [[UselessUsefulSkill Traps]] before you aggro). And many more.
** ''VideoGame/DragonAgeOriginsAwakening'' gives us the Queen of Blackmarsh, a [[NinjaPirateZombieRobot lightning-breathing spectral dragon]] who is quite unambiguously even more powerful than the FinalBoss. Also, the ''[[BrutalBonusLevel Golems of Amgarrak]]'' {{DLC}} has the Harvester, widely regarded as the toughest boss in the entire ''Origins'' saga.
** ''VideoGame/DragonAgeII'' helpfully marks its bonus bosses with dedicated Achievements you get for offing them: a Varterral, a High Dragon, Xebenkeck the Desire Demon (who happens to be an old chum of Gaxkang from part one), and Hybris the Pride Demon. The last one is [[ThatOneBoss particularly bad news]].
** ''VideoGame/DragonAgeInquisition'' has no less than ''ten'' different High Dragons lurking in various areas, as well as the Desire Demon Imshael (also related to Xebenkeck and Gaxkang). Additionally, there is a ''secret'' High Dragon bonus boss, the [[spoiler:Guardian of Mythal]], whom you can only fight after very specific plot decisions, namely [[spoiler:if Morrigan never gave birth to a child with the Archdemon's soul ''and'' did not drink from the Well of Sorrows]].
* In ''Anime/DragonBallZ: Super Saiya Densetsu'', if Goku becomes a [[SuperMode Super Saiyan]] during the final battle with Frieza (accomplished by allowing a party member like Krillin or Chiaotzu to die) and he and Vegeta survive to the end of the battle, after the credits you'll get a scene of Vegeta going Super Saiyan and challenging Goku as payback for the humiliation he suffered back on Earth.
* ''VideoGame/DragonQuest'':
** Divine Dragon/Divinegon in ''VideoGame/DragonQuestIII'' became available to fight after beating the game. You even needed to beat him five times to gain access to all of his wishes. The Game Boy Color version of this game introduced yet another bonus boss, [=GranDragn=]. Getting to this boss required you to complete such a long, boring, and ridiculous fetch quest that even the most hardcore and dedicated gamers have never seen him.
** ''VideoGame/DragonQuestIV'': The DS remake adds an extra chapter after defeating [[BigBad Psaro]]. Explore a new dungeon, fight Foo Yung and Chow Mein, and you have the opportunity to [[spoiler:revive Rosa, get Psaro joining your party and kick the ''real'' BigBad's butt]].
** ''VideoGame/DragonQuestV'': Not including the later remakes of earlier games, this was the first ''Dragon Quest'' to have one of these, as well as an accompanying Bonus Dungeon. Estark, the original form of the final boss of ''Dragon Quest IV'', is the boss. He would become the recurring Bonus Boss for the series.
** ''VideoGame/DragonQuestVI'' has Nokturnus (better known as Dark Dream), who, thanks to his appearances in the ''Monsters'' series, is considered by many to be ''the'' quintessential Bonus Boss of the series. Nokturnus actually gets a little more plot relevance than the average Bonus Boss, in that during the story, you witness a king try to summon him to deal with the BigBad, only to be violently reminded that EvilIsNotAToy. Though, if you're strong enough to put Nokturnus in his place, he really ''will'' deal with the BigBad on your behalf.
** {{God}} in ''VideoGame/DragonQuestVII''. And the four spirits, which is the odd thing since they are supposed to be weaker storyline wise than both the Last Boss and God, yet you can't fight them unless you can beat God easily.
** The Dragon King in ''VideoGame/DragonQuestVIII''. Have fun with the Darksteel Dragon as well; he's a Metal Slime with a lot better attack, who attacks ''three times'', and, just for more fun, he has nearly 2000 HP.
** Half of the bosses in ''VideoGame/DragonQuestIX''. Of special note are the grotto bosses, [[spoiler:who are revealed to be fragments of the Grand Architect Zenus]], and the legacy bosses, the final bosses and some midbosses from every previous serial title (e.g. Dragonlord, Zoma, Estark, Rhapthorne, etc.) The best kind of PanderingToTheBase. You can even opt to give the legacy bosses the experience you gain from beating them, and they will level up each time, to a max of 99.
** ''VideoGame/DragonQuestXI'':
*** There are beefed up versions of the Spectral Sentinels as the bonus bosses of Act 3's BonusDungeon.
*** The Definite Edition and 3DS version has the End of Time, a golden palette swap of the TrueFinalBoss [[spoiler:Calasmos]], who is much tougher than the final boss in question. Exclusive to the Definitive Edition is also the Timewyrm, another golden palette swap, this time of Act 2's final boss [[spoiler:Mordegon]] who is tougher than even the End of Time and takes the cake as the hardest boss in the game.
* ''VideoGame/{{Dubloon}}'' features [[MusicalAssassin The Quartet of the Seas]], a group of four bosses each found in one corner of the ocean. Alone, they aren't dangerous, but just wait until you fight them all four at once in [[BigBoosHaunt the Pirate's Graveyard]]. They ''will'' kick your ass.
* The ''VideoGame/EarthBound'' [[GameMod ROM Hack]] VideoGame/EquestriaBound has a few, who always drop the parties {{Infinity Plus One Sword}}s. According to the hack creator, this was to prevent [[RareRandomDrop Sword of Kings]] situations.
* ''Franchise/TheElderScrolls'':
** ''[[VideoGame/TheElderScrollsIIIMorrowind Morrowind]]'':
*** Due to the game's AnyoneCanDie nature, naturally, anyone in the game can be fought and killed. But special mention has to go to [[spoiler: [[PhysicalGod Vivec]]]]. You are by no means required to fight him, and doing so before completing the main quest will make the normal method of beating the game impossible, but if you choose to do so, you'll have quite the fight on your hands. Bonus irony points if you soul trap him in Azura's Star. This is actually recommended, since he has the second most powerful soul for enchanting in the game, after only [[spoiler: Almalexia]].
*** The Ash Vampires. You are only required to fight one in order to get an item (Sunder) off of him, but there are 6 others you can hunt down and kill. Killing them is supposed to weaken Dagoth Ur in the final confrontation, but due to a scripting glitch, this does not happen (and if it ''did'' happen killing all of them would break the game, as Dagoth Ur ''would be dead before you arrive'' leaving you unable to get the result that's supposed to happen when you kill him). Still, they each possess unique enchanted items that are [[PermanentlyMissableContent unobtainable]] if you don't fight them, and you should kill them if you're going for OneHundredPercentCompletion.
** ''[[VideoGame/TheElderScrollsIVOblivion Oblivion]]'' also has a few.
*** Erandur-Vangaril (a lich). He can only be found in a specific cave that none of the game's quests lead you to, and can only be fought there once your character reaches a certain level.
*** The giant slaughterfish, who shows up in one of the dungeons you explore in the Thieves Guild questline, but chances are you won't ever see this one if you don't fully explore the place.
*** There's also the Uderfrykte Matron at Dive Rock.
** ''[[VideoGame/TheElderScrollsVSkyrim Skyrim]]'' has some as well.
*** The Ebony Warrior of the Dragonborn DLC challenges the player once they reach level 80 in the hope that he's finally met someone tough enough to [[NothingLeftToDoButDie kill him]]. His equipment is heavily enchanted, has 50% damage resistance to all elements, is immune to several spells and Shouts, and can use Dragon Shouts in addition to healing spells and potions. There are also a few named dragons which are not required to be fought. Of particular note is [[spoiler: Vulthoryol, who can be summoned by using the Unrelenting Force shout on the orange globe in Blackreach.]]
*** Also in Dragonborn, the player has the option to fight the ghost of [[LegacyBossBattle Kaarstag]], a Frost Giant that was killed by the [[PlayerCharacter Nerevarine]] in Morrowind's Bloodmoon DLC. The player must find his skull and place it on his throne if they wish to challenge him, and after defeating him they gain the ability to summon him in battle three times only.
*** The Dawnguard DLC adds the Reaper, a ghostly headsman that can be fought in the Soul Cairn after finding three gem fragments.
* ''VideoGame/EpicBattleFantasy'':
** The third game has a bonus room in [[LethalLavaLand Volcano Peak]] that can only be unlocked by collecting all 60 in-game medals. This room has three of these, including a pair of level 50 bushes (in a game where level 30 is the default cap on a first playthrough), a pair of evil worms and their tails (mooks normally only summoned by the FinalBoss), and a trio of one of each type of [[BossInMookClothing monolith]] enemy, all at level 40!
** The Steam release of the fourth game has a whole area dedicated to these, featuring upgraded versions of the main game bosses (except the final boss), the notorious Cosmic Monolith from the third game, and even [[spoiler:evil versions of your party members]]. [[LegacyBossBattle Some of the bosses from the second and third games]] also return in the main game as optional minibosses. The main game also includes the Glitch, a PuzzleBoss based on using NonElemental skills and preventing OneHitKill attacks.
** All versions of the fifth game have the return of the Glitch boss after completing four "glitched" areas and an ''VideoGame/{{Undertale}}''-styled cat boss known as Snowflake after gathering three gems hidden in chambers underground. The first Steam version added harder versions of the four main non-FinalBoss[=es=] (and the Hydra minibosses) in their own mini-dungeons, and beating them grants access to [[spoiler:''alternate'' evil versions of the party members that are more distinct from the Dark Players of the fourth game]]. Version 2 added even more: a BossBonanza of four sketches in the expanded Greenwood Library, twelve hidden 8-bit Arcade minibosses with some sort of central gimmick scattered around the world, [[NostalgiaLevel and eight bosses from the previous games (two from each game) in a series of bunker simulations.]] All of them scale to the players, based on things like level, medals obtained, and how many ''other'' optional bosses and challenges have been completed.
* ''VideoGame/EternalTwilight'': In the Seraphic Shrine, the party can challenge revamped versions of story bosses, ending with a fight against [[spoiler:El Puerco, a powerful extradimensional pig that threatens to destroy entire worlds]].
* The ''VideoGame/EtrianOdyssey'' series as a whole has a '''''LOT''''' of bonus bosses; many of them are usually part of {{Side Quest}}s, and about half of them are post-end game only.
** Prevalent in all games except the fifth are the post-game [[FireIceLightning three elemental dragons]] (Great Dragon, Blizzard King and Storm Emperor), who each has an elemental attack that can wipe out your entire party in one hit unless you negate it with specific skill at the right time. From the third game onwards, their defeat also raises the level cap for your entire guild -- an important asset for the postgame.
** Even before end game, there're usually a few bosses that can be fought early on, but definitely not recommended as they are usually far too powerful that early. The Wyvern and Salamander from the first two games are good examples.
** The third game, ''The Drowned City'', introduced a second exploration map (the sea), thus ramping up the number of bonus bosses in the game. Same deal with the fourth game, ''Legend of the Titan'', and its skyship map.
** Finally, to top it off, each game has a BonusDungeon that houses the TrueFinalBoss of the game, and it goes without saying that they are excruciatingly difficult, sometimes requiring strategy guides that lists what they will do ''turn by turn'' just for you to have a chance to beat them.
** In absence of the elemental dragons, ''Beyond the Myth'' has an all-new catalogue of Bonus Bosses: Dryad in Tutelary Forest, the Primordiphant in Jagged Reach, the Zombie Dragon in Fetid Necropolis, Lamia in Lucent Hollows, and [[spoiler:Star Devourer (the one who killed Arken's race)]] in the BonusDungeon. The Primordiphant is the only one that makes an appearance during the main story, and the objective at that point is to figure out how to ''avoid fighting it'' (the sidequest tasking you to face it will only pop up after the main story is completed); all others will start appearing one by one in the postgame.
* Ultimate Weapon and Khaer Magnus in ''VideoGame/{{Everlong}}''. To mention just the really tough ones.
* ''VideoGame/{{Fallout}}'' has had several of these across all the games in the series.
** ''VideoGame/Fallout3'' has five or six [[AttackOfThe50FootWhatever super mutant behemoths]] who you can hunt down. Admittedly, one is a MiniBoss over the course of the main story, but even then, you could just skip the entire section. Other optional bosses include Commander Jabsco of Talon Company, Lag-Bolt and Enclave Squad Sigma in ''Broken Steel'', and the three Ant Queens.
** ''VideoGame/FalloutNewVegas'' has the BigBad himself, Caesar. Especially compared to his second-in-command, Legate Lanius, Caesar is pretty weak for a boss, only being about as tough as an EliteMook. However, he's in the middle of the Legion's stronghold, and his personal section (the only one you're allowed to visit) is crawling with dozens of Legion troops. When you get past them, he is protected by eight {{Praetorian Guard}}s armed with [[PowerFist shotgun fists]], each of which is as powerful as him. At lower levels, Caesar and his guards will usually dogpile you into a corner and beat you to death in a few hits, since said shotgun fists do ridiculous damage and Caesar and his guards are ''fast''. However, if you go there at a later level with a good companion and high level weapons they'll go down easily enough.
** The four (five with ''Old World Blues'') legendary creatures in ''New Vegas'', which are [[UndergroundMonkey reskinned]], [[GiantMook upsized]], and [[ThatOneBoss overpowered]] versions of their normal species. Admittedly, a sufficiently leveled character can make short work of most ([[spoiler:Legendary Cazador, Legendary Nightstalker, and Legendary Fire Gecko]]) but the [[spoiler:Legendary Deathclaw]] from the main game, and [[spoiler:[[LethalJokeCharacter Legendary]] ''[[TheGoomba Bloatfly]]'']] from ''Old World Blues'' can usually kill you in... Two hits. Almost always.
** There's another boss Deathclaw in ''Lonesome Road'', named Rawr. It's a LightningBruiser, even compared to the Alpha Male, and will kill most characters in one hit; it has somehwhat less HP than the Legendary Deathclaw. Defeating him allows you to build one of the most powerful Unarmed weapons from his talons, Fist of Rawr. [[spoiler: Or [[Manga/FistOfTheNorthStar Fist of the North Rawr]] if you have [[SillinessSwitch Wild Wasteland!]]]] There's also Gaius Magnus and Colonel Royez, who are only available [[spoiler:if you choose to nuke the Legion or NCR respectively at the end.]] Both have all of their special stats maxed out, and Royez has the third highest HP of any human enemy after Ulysses and Legate Lanius, a Damage Threshold of 24, wields a plasma caster with overcharge ammo, and regenerates his HP very quickly from the radiation.
** ''VideoGame/Fallout4'':
*** Swan, a special Super Mutant Behemoth, resides in the Boston Common's duck pond and wields a gigantic hammer fashioned from an anchor. Defeating him nets you the armor-piercing Furious PowerFist.
*** The optional Quincy Ruins is home to three Gunner leaders, who are backed up by many high-level mooks from the overpasses and other high ground. Two of the bosses wear PowerArmor, and the one that doesn't, Sgt. Baker, is armed with a OneHitKill Fat Man. Clint wields an Engraging Laser Rifle named Good Intentions, and Tessa wears a unique Raider Power Armor Right Arm named Tessa's Fist (not a PowerFist, [[NonindicativeName despite the name]]). Other Gunner bosses include Captain Wes in the Gunner Plaza, and Captain Bridget at Hub City Auto Wreckers.
*** The Far Harbor DLC has a randomly-encountered legendary Fog Crawler named Shipbreaker. Given that normal Fog Crawlers are already [[BossInMookClothing Bosses in Mook Clothing]], this one's insanely difficult to take down, especially because, being a Legendary, it TurnsRed and auto-heals when its HP is depleted halfway the first time. Reporting its defeat to Longfellow earns you the Skipper's Last Stand harpoon gun, which grants +150 damage resistance when reloading.
* They exist in many ''Franchise/FinalFantasy'' games:
** Ruby Weapon and Emerald Weapon in the international version of ''VideoGame/FinalFantasyVII''.
** ''VideoGame/CrisisCore'' has Minerva. Genesis's best form is ''nothing'' compared to her.
** ''VideoGame/FinalFantasyVIIRemake'' currently ends at the Midgar storyline, but it has two of them. The first one involves completing all of Chadley's reports for the right to challenge Bahamut for his summon materia. Completing all of the Wall Market Colisseum battles and Shinra VR battles, especially on Hard mode, allows you to go through a gauntlet of all the summon bosses to face Pride and Joy, an EarlyBirdCameo of the Proudclod boss fought near the end of the original game's Disc 2. Even worse, you can only do this challenge on Hard.
** Ultima and Omega, or Ultima Weapon and Omega Weapon, appear in many of the games, including ''VideoGame/FinalFantasyV'', ''VideoGame/FinalFantasyVI'', ''VideoGame/FinalFantasyVIII'', ''VideoGame/FinalFantasyX'', ''VideoGame/FinalFantasyX2'', ''VideoGame/FinalFantasyXI'', ''VideoGame/FinalFantasyXII''. Omega also features prominently in ''VideoGame/DirgeOfCerberus''. Ultima was a mandatory boss in ''VideoGame/FinalFantasyVII'' as well as ''VideoGame/FinalFantasyVI'', under the name Atma Weapon. Omega and Ultima are storyline bosses in XI's Chains of Promathia expansion, and are {{Sequential Boss}}es to boot.
** The Monster Arena monsters in ''VideoGame/FinalFantasyX'', and the Dark Aeons and Penance in the International/HD versions. Some of the Dark Aeons were required encounters if you want to backtrack to certain areas. Penance is entirely optional, and he's accordingly brutal... 12 ''million'' HP, potent attacks that devastate an unprepared party, and supporting limbs that do even more fun damage.
** The Via Infinito monsters, led by Paragon and Trema, in ''VideoGame/FinalFantasyX2''. Black Elementals with the ability to just use Ultima at 255 magic whenever it wants, Chac for bypassing stone status resistances or debuffing all stats by TEN with Heaven's Cataract or Concherer who isn't too bad but IS a brick wall of defense.
** The Fiend Arena in the International/HD re-release of ''X-2'' has quite some nasty customers in their tournaments. Expect daunting foes such as Bahamut with over 100,000 HP and a sure-hit kill attack for 9999 damage per girl (all used at leisure), enhanced human enemies (Baralai, Nooj, Gippal, etc) with jacked up stats and brand new cheapo moves to annihilate before a chance is had. The toughest, though, is Almighty Shinra, with potent spells meant to decimate the party right off the bat, and regular nasties such as Paragon and Trema above as regular battles.
** ''X-2'' also gives us Major Numerus, a four headed, four staged boss with tons of abilities to decimate the characters. It's required to fight him with three Iron Dukes equipped (one girl a piece) or else you're just wasting your time.
** Hell Wyrm, Yiazmat, Behemoth King, the eight non-story line Espers (which includes Zodiark), Omega Mk. XII, etc. in ''VideoGame/FinalFantasyXII''. To date, Yiazmat is the boss with the most HP in all of ''VideoGame/FinalFantasy'' (a grand total of ''[[MarathonBoss 50 million]]''), and can take multiple rounds to defeat. To make matters worse, Yiazmat is a rare Bonus Boss that requires a Bonus Boss to even begin the side mission -- the [[NamesToRunAwayFromReallyFast Hell Wyrm]].
** ''VideoGame/FinalFantasyTacticsA2'' had Upsilons A1 (leveled somewhere in the 60s) and A2 (Level 96) and the Level 99 mage clan.
** ''VideoGame/FinalFantasyI'' had a [[BossInMookClothing special secret random encounter boss that was only able to be encountered on the walkway heading towards Tiamat.]] The boss was a mecha named Warmech and had damage capabilities surpassing Tiamat.
** The remake of ''VideoGame/FinalFantasyI'' in ''Dawn of Souls'' for the GBA included optional dungeons with bosses from ''III, IV, V'', and ''VI''; only Omega and Shinryu from ''V'' were much harder than the regular FinalBoss.
** The PSP VideoGame/FinalFantasyI remake ups the ante with Chronodia, who has ''eight forms''. It's not a SequentialBoss, though; which one you fight depends on how you did in the BonusDungeon prior to fighting her. Either way, she's pretty hard.
** In ''VideoGame/FinalFantasyII'', the [[InfinityMinusOneSword Infinity-1 Weapons]] and strongest armors are stored in chests in the final dungeons, guarded by powerful monsters. The Soul of Rebirth bonus mode also has Ultima Weapon, which grants the Ultima spell to Minwu upon defeat.
** The ''20th Anniversary Edition'' of ''VideoGame/FinalFantasyII'' has a sideplot revolving around the character of Deumion the guardian. It includes two new superbosses at the end of the Arcane Labyrinth. One is Phrekyos: a badass-looking HellHound summoned forth by Deumion to test your strength. It's both a capable mage and a hard hitter. The second is Deumion himself, but only in case you wish to get the UselessUsefulSpell Destroy that he guards with his life. Deumion's not really hard, but he's got more HP than any other enemy in the game and can cast the Dark Emperor's Starfall spell, among others.
** ''VideoGame/FinalFantasyIII'': The DS and later versions have the Iron Giant, a beast with [[StoneWall massively high defense]], powerful physical attacks that cause [[StandardStatusEffects a wide variety of status effects]], the [[DeathFromAbove Meteor]] spell, and who gets four attacks per round. [[TurnsRed After you've depleted enough of his HP]], his regular attack gets replaced with one that does double damage and hits all party members at once. Have fun!
** ''VideoGame/FinalFantasyIV'' had four optional boss fights against [[SummonMagic Eidolons]]: Asura, Leviathan, Odin, and Bahamut. Only one of these was particularly difficult. The others required very specific strategies rather than a highly leveled party to defeat, making them closer to {{Puzzle Boss}}es than anything else. This was fitting, as the battles were intended to be [[DefeatMeansFriendship tests of your skill]]. Furthermore, several powerful weapons and armor in the final dungeon are guarded by horribly powerful PaletteSwap bosses, including one that hits the entire party with unblockable Doom when the fight starts (giving you a time limit before TotalPartyKill). The GBA version added some more, most notably, a modified version of Easytype Zeromus and Brachioraidos, a dragon tough enough to be a superboss even relative to the BonusDungeon it appears in. The DS remake removed most of those added by the GBA version, but features two new optional bosses only accessible through NewGamePlus: Geryon and Proto-Babil.
** ''VideoGame/FinalFantasyIVTheAfterYears'' features the return of the below-mentioned Omega and Shinryu in the [[BossBonanza final]] [[MarathonLevel dungeon]], as well as [[VideoGame/FinalFantasyVI Deathgaze and Ultima Weapon]]. The PSP version adds Lost Babil, a humungous mecha that requires a completed file and three parties to fight it: one for the lower body, one for the upper body, and one for the inner CPU, which can be repeated indefinitely for Soma Drops and Silver Apples. The PC version removes the crossover bosses and adds back some of the bonus bosses from ''Final Fantasy IV Advance'', including Lunar Odin, Lunar Leviathan, and Lunar Bahamut.
** ''VideoGame/FinalFantasyVI Advance'' as three new boss espers: Leviathan, Gigantuar, and Gilgamesh. There are also five bosses found wandering in a pit within the Dragon's Den - Dark Behemoth, Abyss Worm, Gargantua, Earth Eater, and the Malboro Menaces and bosses-in-chests: Neslug, Plague, and the Flan Princesses, which use massive recovery, Doom to all, and Berserk to all, respectively. Kaiser Dragon is a monster that was DummiedOut of the original game and, due to having an associated monologue, seems to have been intended to have been a bonus boss in the original version, but to have been cut for time. The entire BonusDungeon leading up to him is full of bonus bosses, in the form of souped-up versions of the Eight Dragons, each much stronger than other bosses in the game.
** ''VideoGame/FinalFantasyV'' had two of these, Omega and Shinryu, both who gave [[CosmeticAward trinkets praising your deed]] upon death, and who made Neo Exdeath look like a marshmallow peep in comparison .
** ''Final Fantasy V Advance'' was especially brutal with these, creating a BonusDungeon full of them. This included such prestigious opponents as [[spoiler:Enuo, the frickin' original creator of The Void, which was the Main/MacGuffin that was Exdeath's entire goal, and something that he couldn't control in the end;]] Omega MK II and Neo Shinryu, souped-up versions of the bonus bosses of the original game, both of whom made their originals look like marshmallow peeps in comparison (Omega MK. II was very notable, housing a huge floor full of copies of Omega, each one as strong as the bonus boss of the same name, proving just how much stronger the players had to be to stand a chance.)
** ''VideoGame/FinalFantasyVIII'' has several, some of whom will join you as Guardian Forces once defeated. The Brothers are optional, as are the Jumbo Cactaur and Odin. Diablos best fits the description, as he's designed to grow in power at the same rate as the main party, thus making him a tough challenge at any level.
** Ozma (unique in that his difficulty has little to do with inflated stats and almost everything to do with proper strategizing, albeit with more than a hint of Main/GuideDangIt) and Hades in ''VideoGame/FinalFantasyIX''. Kinda complementary - Hades turns out to be a legendary synthesist, and one of the rewards for beating Ozma is something you can synth off to obtain Ark, the ridiculously over-the-top summon. There's also the Tantarian, another boss whose difficulty is based on strategy rather than just stats. Beating him nets an accessory that teaches the very useful Auto-Haste ability.
** ''VideoGame/FinalFantasyXIII'' continues the tradition with Vercingetorix, boss of the final [[SideQuest Mission]]. This bad boy has 15.8 million hitpoints and can't even be accessed until after you beat the game. But it's easier to beat by simply poisoning him and then guarding for the entire battle; this is because poison deals damage based on maximum HP, and Vercingetorix, as mentioned, has a ''lot'' of it. Long Guis also have even more HP, huge stats, and immunity to every form of status debuffs compared to Vercingetorix.
** ''VideoGame/FinalFantasyXIII2'' features several optional bosses, three of which are absolutely brutal. The Long Gui returns, and despite only having a quarter of the HP it had in ''XIII'', it's still extremely tough to put down. Yomi is a weaker (but still formidable) version of Vercingetorix. And finally, there's Raspatil, a horrifyingly powerful Undying Cie'th that's probably the hardest fight in the vanilla game.
** The DLC Coliseum battles in ''VideoGame/FinalFantasyXIII2'' are all nasty, especially Jihl, the one person everyone who played ''XIII'' wanted to kill and Gilgamesh, who has almost 10 million HP and can heal himself. The most notorious monsters in the Coliseum, however, are Snow and Valfodr. First off, before you can fight Valfodr, you fight Snow, who has 10 million HP, and if you don't provoke him into attacking someone else and he continues to attack the same character for a set amount of time, he will use a TotalPartyKill attack. Once you defeat him, you fight Valfodr, who has five increasingly difficult forms, progressively getting harder.
** ''VideoGame/LightningReturnsFinalFantasyXIII'' has its own flavor of Bonus Bosses. In the first playthrough you are capable of taking on the game's two superbosses, the Aeronite and Ereshkigal. Afterwards, if you go on to play Hard Mode, they can be fought again; [[SerialEscalation their stats and health go through the roof]], with Aeronite getting [[UpToEleven potentially 50 million HP]].
** ''VideoGame/FinalFantasyXIV'' has the Ultimate Trials which are this for even the most well-geared out 8-man parties, being not only [[MarathonLevel a test of endurance]] but also [[FinalExamBoss a test of every skill each class role can fill to their extent]]. They can only be unlocked by defeating the final boss of a Savage Raid Tier, in this case Neo Exdeath, God Kefka and Titan Maximum.
** ''VideoGame/FinalFantasyXV'':
*** There are two in the base version: The first is the the Adamantoise, which is probably the largest boss ever in the series and also one of its longest encounters taking about 3 in game days, or 2 hours in real life to defeat. Beyond that, the game shipped with three other notables in Naglfar, Ayakashi, and MA-X Angelus-0, with the former two being the only enemies to break the launch level cap, and the later being a [[BossInMooksClothing random encounter]]. Several others have been added as DLC since release.
*** Royal Edition added the recurring bonus boss Omega as a Solheim superweapon forged to fell the Astrals. And surely enough, it was indeed imprevious to attacks from them and conventional weapons. Only Royal Arms and top-tier Elemancy spells could do a dent against Omega, though the immunity switched from conventional weapons to Royal Arms whenever it TurnsRed.
* ''VideoGame/FossilFighters'':
** There is a ''huge'' slew of bonus bosses, one of which opens up before the final boss, and the rest of which appear afterwards, in the PlayableEpilogue.
** The lone bonus boss available before the game's end is Petey, a dino battler who demands to fight a team of three specific dinosaurs. If you take the time to grind those three specific dinos, he's managable, but if you're anything less than maxed, be prepared to hurt from it.
** But ''after'' the final boss? Both Saurhead and the [[TerribleTrio BB Trio]] reappear with "marathon battle" bosses, where you have to beat three of their teams with no break in-between. They're tough, and your reward is [[spoiler: the OlympusMons]] from waaay back at the game's halfway point. You can finally fight Dr. Diggins, though he offers up nothing but [[BraggingRightsReward bragging rights]] (and EXP, if you're looking to grind). You can fight a samurai who's been in the hotel room next to yours [[ChekhovsGunman for the entire game]], whose most notable trait is that his Trainer rank is [[UpToEleven one beyond "Master."]] Oh, and if you're feeling lucky, punk, you can go back to [[spoiler: the dinaurian spaceship]] and challenge [[spoiler: Duna, Raptin, and Dynal--all at once.]] And ''that isn't even all of them!''
** The sequel, ''Fossil Fighters Champions,'' follows suit. In addition to almost all of the important characters having high-ranked teams you can fight in the PlayableEpilogue, there's a ''bonus tournament'' that culminates in a fight against [[spoiler: Rosie from the previous game.]] There were also DLC bonus bosses--including a strange character named Ryne, who gives you a new legendary vivosaur for winning, and [[spoiler: Duna, Raptin, and Dynal again]].
* All the ''VideoGame/{{Geneforge}}'' games have an 'Expert' level dungeon with the toughest Bonus Boss in the game. Most of them generate repeated creations to add to their attack power, and traps that deal extra damage unless the player has the skill to disable them or at the least reduce their effect. The worst is the Titan of ''Geneforge 4'', which each time it was weakened to low health would shift to a new form, with a new set of attacks, defenses and vulnerabilities, requiring the player to have mastered a wide range of combat abilities. And of course, leaving the dungeon to rest also reset this Boss to its original form and strength.
* ''VideoGame/GoldenSun'':
** ''VideoGame/GoldenSun1'' has Deadbeard, an undead pirate found at the bottom of Crossbone Isle, who guards the game's most powerful armor. One path to him contains another bonus boss, a weather controlling lizard. A third bonus boss has its own bonus ''Town'' outside the BonusDungeon, and is a gigantic acid frog.
** ''VideoGame/GoldenSunTheLostAge'' has the Star Magician, Sentinel, Valukar, and Dullahan. The [[FlunkyBoss Star Magician]] summons mooks to use Jupiter psynergy on you, buff and heal the Magician, and explode for huge damage. Sentinel constantly buffs his defense and is immune to all psynergy, meaning he gets tougher and tougher. Valukar can knock your Djinn into Standby and use your summons against you with Crucible. And [[MemeticBadass Dullahan]] can put every active party member's Djinn into recovery with Djinn Storm, gets three moves per turn, and hits like a runaway cement mixer.
** In ''VideoGame/GoldenSunDarkDawn'', Star Magician and Dullahan get buffed up, with Star Magician getting three new mook types (Curse, Death, and Ghoul) and Dullahan getting Valukar's Crucible move. There's also the Ogre Titans, a group of five increasingly powerful physical attackers, and the Ancient Devil, who can take over one character with Demon Sign.
** In the early parts of ''Dark Dawn'', if you try to beat the Psynergy Training Grounds a second time, the Dim Dragon gets an upgrade, making it an early-game Bonus Boss.
* ''VideoGame/GrandiaXtreme'', rather than a new and unique boss, gave you the chance to go back to the old dungeons after beating the final boss, and in one of them you can fight a super-powered level 200 version of a boss you already faced.
* The Doppelganger in the ''VideoGame/DotHackGU'' games is optional, but is ridiculously difficult and gives some of the most powerful weapons in the games.
* ''VideoGame/IcewindDale II'' has two of these, both within the same chapter. The first is a [[spoiler:black dragon in the "Crossroads", which can be killed to close the teleport to Kuldahar.]] Players don't actually have to fight it, and can achieve their goal in a much easier way, but the difficulty of the battle alone makes it worth it for many players. The other boss is [[spoiler:the Six Lost Followers, in the Kuldahar graveyard. This is regarded by many to be the hardest fight in the game, because A) there are six different enemies to fight at once, B) they are several levels higher than your party, and C) because each has only a few specific weaknesses, being immune to all other forms of attack, and with the weaknesses being different between each member.]] Victory gives the player the Holy Avenger, the best weapon in the game. Unfortunately, this pisses off quite a few people itself, as the weapon can only be wielded by a Paladin, meaning that there is no reward for anyone without a Paladin in their party.
* ''Franchise/KingdomHearts'' has plenty, and tends to use the toughest ones as [[SequelHook walking sequel hooks.]]
** [[VideoGame/KingdomHeartsI First game]]:
*** The Clock Tower Phantom (gives you the last Stop spell upgrade), as well as many of the tournaments.
*** The international release of the first game [[RegionalBonus added]] [[VideoGame/FinalFantasyVII Sephiroth]], [[WesternAnimation/{{Hercules}} Ice Titan]], and Kurt Zisa. While the only prizes for beating them in that version were experience and bragging rights, the Final Mix version gives you decent rewards for beating them (the physically inclined One-Winged Angel Keyblade for Sephiroth, the magically inclined Diamond Dust Keyblade for Hydros, and the Zantetsuken ability (which gives Sora a OneHitKill attack, though it doesn't always work) from Kurt Zisa). It also adds the Unknown, who is easily the hardest boss in the game. This is justified immensely when you find out who he is: [[spoiler:Xemnas, the BigBad of ''Kingdom Hearts II''.]]
** [[VideoGame/KingdomHeartsII Second game]]:
*** In the international release, the only boss that you don't have to fight to beat the game is Sephiroth; like the first game, you have to fight him one-on-one, and he's ridiculously tough. Aside from that, the only things that could count are the Coliseum tournaments.
*** The third level of the Assault of the Dreadnought gummi ship course ends with a boss fight against the Hunter-X, which has every SpamAttack that the other enemy ships do plus an attack that's easily strong enough to one-shot most of the player's ships and hits half the screen.
*** The Final Mix version went overboard with this: First, there are the five Absent Silhouettes, shadowy spirits of the members of the Organization who had died in [[VideoGame/KingdomHeartsChainOfMemories the previous game]] that have different tactics and a different level of strength since then. But those are child's play compared to what you can access after you've beaten the game; at the end of Hollow Bastion [[spoiler:/Radiant Garden]]'s BonusDungeon, the Cavern of Remembrance (itself a trial to get through), you find the Garden of Assemblage, where data replicas for all thirteen members of the Organization await, and their threat levels are jacked UpToEleven. But none of those replicas, not even Xemnas, can match the last Bonus Boss in the game: a mysterious armored Keyblade Master named the "Lingering Will", found through a portal in Disney Castle. He is hands-down ''THE hardest boss in the game''...and like the Unknown, it's very easily justified when you find out who he is: [[spoiler:Terra’s soul, trapped inside his armor after Master Xehanort took over his body in ''VideoGame/KingdomHeartsBirthBySleep'']].
** ''[[VideoGame/KingdomHearts358DaysOver2 358/2 Days]]'': Dustflier. He can be found before beating the game, in a late-game mission where the goal is to defeat six bosses scattered through Twilight Town in succession, and only appears after all six are dead. And while you can ''complete'' the mission by only taking out the first six, you have to go and finish Dustflier to fill up the extra portion of the Mission Gauge, which is part of HundredPercentCompletion. (Fortunately, ''358/2'' allows you to redo missions at will.)
** ''Kingdom Hearts Re:Coded'' has [[spoiler:Buggy Roxas]], a powered-up, Heartless version of the already [[ThatOneBoss very hard]] [[spoiler:Data-Roxas]]. The best strategy to beat him is to nail down his pattern, spam Dodge Roll whenever he gets even near close to you and try to cheat his AI so that he doesn't use ThatOneAttack [[TurnsRed when he's low on health, where all his stats are doubled and he becomes gigantic]]. [[ThatOneSidequest You need to beat him to earn the]] [[InfinityPlusOneSword Ultima Weapon]].
** ''Birth by Sleep'' brings its own Bonus Boss, [[spoiler:Vanitas Remnant]], notable in that he only has one health bar because he's JUST THAT HARD TO HIT. If you heal yourself during the battle, he ''also'' heals himself. Completely. [[spoiler:Unless you use potions instead of magic.]] The Iron Imprisoner and Mimic Master are optional Unversed bosses that only appear in the Mirage Arena, though they're not nearly as formidable as the Remnant.
** ''Birth By Sleep''[='=]s international release adds a new boss, another Unknown: the English speaking fandom calls him "The Mysterious Figure", a name taken from the strategy guide, to differentiate him from the first Unknown. [[spoiler:He's revealed to be a time-traveling young Xehanort in Kingdom Hearts 3D.]] A black-coated, dual-laser-blade-wielding mofo, this boss has put the rest of the series's [[ThatOneBoss famously batshit insane and bullshit hard bosses]] to shame. So far, the only known strategies for beating it are "Spam Dodge Roll with Ventus and pray" and "Spam Thunder Surge with anyone and pray".
** ''Birth by Sleep Final Mix'' adds three more bosses that can be fought in the Mirage Arena: [[WesternAnimation/{{Pinocchio}} Monstro]] and the armors of Master Eraqus ("Armor of the Master") and Master Xehanort ("No Heart").
** ''Dream Drop Distance'' has [[WesternAnimation/RunawayBrain Julius]], featuring heavy defense and powerfully strong attacks. And one of his combos doesn't set off Once More, only Second Chance, meaning you WILL die if you're unlucky, and another attack so powerful that not only does it eat up all of your HP, but it disables your active command. God help you if you only pack one Curaga and kept the cursor on it. The worst part, the only way to know which way to dodge for the attack is to use the bottom screen, which you never use during any other fight, to see where his icon is headed. And you're not allowed to bring your Dream Eaters into the fight.
** ''0.2 Birth by Sleep -A fragmentary passage-'' has a bonus BossRush. It starts with a Darkside, two waves of Heartless, and a Demon Tower, but the final opponent and the true contender of Bonus Boss? A buffed version of [[MirrorBoss Phantom Aqua]], who is essentially THE hardest boss of the game. Since you've fought her three times already, you'd think she'd be a pushover, right? Wrong. This version has plenty of new and old attacks (some of which are unblockable, indicated by [[ColorCodedForYourConvenience red trails]]), little openings to strike, and is incredibly strong, too. You'd better be ready for her, or else she'll wreck you.
** ''X'' gets in on the action with Event Raids, raid bosses encountered through a specific event. And ''holy shit'', can they soak damage. The first really bad one, the first Halloween’s Fortress Crab raid, had ''99,000,000'' HP at ''level 1''. Later ones can take a pounding from even the most powerful parties whaling on it with the metagame’s top medals. Fortunately, pack a few defense boosting medals with your attack boosts and you can just leave the raid running(with the game’s nifty [[AntiFrustrationFeatures auto attack button]]), and go do something else while your character slaughters it.
** ''VideoGame/KingdomHeartsIII'' (pre-DLC) has Dark Inferno, a dual-wielding Heartless with fast & brutal attacks and high speed. Good luck on Critical. There's also the bonus boss in the Gummi Ship sections, the [[VideoGame/{{Einhander}} Schwartzgeist]], a battle of attrition with one-hit kills.
*** With the DLC, we get a golden version of Dark Inferno, a more powerful Armored Xehanort with 13 Dark Keyblades, the return of the Data Organization, and the SequelHook superboss Yozora.
* While it's "only" a Mod, the ''VideoGame/KnightsOfTheOldRepublic Brotherhood of Shadow'' [[spoiler:has a flashback to Malachor V]]. You're stripped of all your gear, and [[spoiler:have to re-create the single-combat against Mandalore that ended the Mandalorian Wars]]. Comparatively, the canonical FinalBoss fight against Malak is nothing.
* The Gargoyle in ''VideoGame/{{Koudelka}}'', on Disc 3/4. At the same time, it's also ThatOneBoss -- because even for a bonus boss, it is just insane. Also, it's a HopelessBossFight on Disc 2 -- when the titular heroine fights it alone, she'll deal no damage and will be forced to run away.
* ''VideoGame/TheLastStory'' has [[spoiler:Therius]] and [[spoiler:Gigamuruk]]. The first is a one-on-one DuelBoss who can only be challenged with Zael alone, in a callback to an earlier boss fight. The latter is fought at the conclusion of the game's running TournamentArc. In both cases, you have to wait until the PlayableEpilogue to look for them.
* ''VideoGame/TheLegendOfDragoon'':
** In the dungeon before the PointOfNoReturn, you are given the opportunity to fight the spirits of the three dragons you defeated. They drop some useful attack items, and they're also guarding chests containing powerful equipment.
** There's also the Poltergeist-posessed armor set in Fort Magrad, an optional section of the Snowfield on Disc 3 (you travel through this area on your way to Velwebb. Hint: the sword has an instant-kill attack and it always uses it at the character who manages to dispatch it.
** There's also the four Dragoon ghosts in Velwebb, and Magician Faust at Flanvel Tower, who is the most powerful enemy in the game. Beating him does get you a great reward though in the Phantom Shield along with 30,000 gold. Here's everything you have to go through to get to him, which definitely puts him in this trope by the above definition: Throughout the game, there is a side quest to collect a total of fifty stardust scattered throughout the continent. Every tenth stardust, when shown to the proper character, will give you a different item. The final item is a mirror that is required in order to face Faust. Faust is an insanely powerful Wingly who was second-in-command to Melbhu Frahma, but ends up being a dozen times more dangerous, possibly due to having been alive and studying/training for the entire time his "boss" has been asleep. You then have to find the entrance to Flanvel Tower, following a winding maze of teleporters just to get to the tower. If you do not have the mirror in your possession the first time you see him, he WILL kill everyone in your party with one blow a piece, and you will be unable to touch him. As it turns out, this first Faust is merely a projected image. The real Faust is able to cast his magic through the image even while being twice as deep in the dungeon. And so, obviously, you must finish the maze.
* In ''VideoGame/TheLegendOfHeroesTrailsOfColdSteel IV'', defeating every cryptid that can be found throughout Erebonia, and completing special quests during the final chapter will lead to Argres, the Holy Beast of Earth. He's exceptionally tougher than [[spoiler:Osborne]] and prone to utilizes charged magic with physical strikes to inflict status aliments. Once beaten, he'll give Rean a special divine object that will lead into the true ending.
* ''VideoGame/LegendOfLegaia'' has Lapis, who has insane attack power and can incapacitate a party member with a string of vicious attacks that deal upwards of 200% of the character's HP. Beating this boss requires either a lot of luck, hours of LevelGrinding, or using a very specific accessory setup. [[note]]Specifically, equipping the Luminous Jewel accessory. Since Lapis's attacks are Light elemental ([[GuideDangIt The game does not mention this.]]), using this accessory cuts his damage output in half and makes his attacks survivable.[[/note]]
* ''VideoGame/LiarJeannieInCrucifixKingdom'' has the two elite Pleiades Knights, [[DualBoss Celaeno and Alcyone]], [[spoiler:who guard the exit of the kingdom and must be defeated to get the secret ending.]]
* ''VideoGame/{{LISA}}: The Painful RPG'' has a giant man who goes by "Satan,"[[note]]His actual name is Mike, which he tells you when he's dying[[/note]] found inside a truck on an off section in the Eternal Wrestling Championship that links Area 2 and 3. The keys to his truck are guarded by the Joy Mutant "Beady," itself a difficult and optional boss. He is one of the hardest bosses in the entire game, having a lot of health and access to an instant-kill move, but he drops one of the best equipment pieces as a reward. To emphasize his difficulty, he has an ominous buildup to him, with the NPC outside his valley telling Brad that nobody who has gone in the "Devil's Machine" (his truck) came out alive, the screen tinting red as Brad gets near the truck, and a mild JumpScare-honk playing when in front of it.
* ''VideoGame/LiveALive'' features several ultra-tough hidden bonus bosses. The caveman chapter has King Mammoth, who offers a decent reward in the King's Fang, as well as the randomly dropped "Soda." The ninja chapter has Majin Ryunosuke, who can be beaten for a weapon that you can also get at the end of the chapter if you don't kill anyone, and Lord Iwama, who drops an item that can deal a decent amount of damage if used in battle. The final chapter has about five, four of which drop the most useful equipment in the game.
* ''VideoGame/LostOdyssey'' has seven: Persona, King Kelolon, the Cave Worm, the Blue Dragon, the Holy Beast, Legendary Spirit Sorcerer Fu, and The Immortal One in the Backyard. Players with access to UsefulNotes/{{XBox Live|Arcade}} can get a new downloadable dungeon with an extra boss [[spoiler:Professor K, aka The Killalon]].
* ''VideoGame/{{Lunarosse}}'' has two post-game bosses. One is implied to be a GreaterScopeVillain for the creator's future projects and the other tied into the SequelHook.
* ''VideoGame/ManaKhemiaAlchemistsOfAlrevis'' had 5 Bonus Bosses in total: four that were cameos from other Gust games, and the fifth is a PaletteSwap of the TrueFinalBoss. Each of them are fought individually, but later three of them can team up for a sixth battle, which can be ''very'' difficult if the player's not prepared. The only saving grace for that battle is their common [[WeaksauceWeakness vulnerability to a certain character's]] ''[[WeaksauceWeakness normal physical attack]]''.
* ''VideoGame/{{MARDEK}}'':
** Chapter 2 has the Zombie Dragon, located in Social Fox Tomb, accessed after the first battle with Moric. It has ''11000+ HP'' and can inflict most [[StandardStatusEffect status effects]], though he goes down rather easily if you have Vehrn and Mardek equip a Silver Sword (Or replace Vehrn with Zach and have the boneslicer equipped) and have Quarry:Undead active.[[note]]Vehrn also has Smite Evil and Disrupt Undead, making him a better choice than Zach.[[/note]] Upon defeat it drops the Burial Sword, the best weapon for Deugan in the chapter.
** Chapter 3 has Annihilator:Karnos fought in the [[EldritchLocation Miasmal Citadel.]] In addition of starting with Haste, having ''[[MarathonBoss 66,000 HP]]'', can also [[BarrierChangeBoss change its element]] either when taking a turn or reaction to magic attacks in addition of hitting like a truck to the entire party without proper resistance. He can and will dispel Haste and/or shields if you have them up.Defeating him gives you the Guardian Claw, the best weapon for Solaar in the chapter, Scarab of Fury and is also required to fight the boss below.
** Annihilator:Animus, which, despite having lower HP than Karnos and can't change elements, is actually ''even stronger''. Fought in the [[SpiritWorld Dreamshrine]], it starts the battle with Haste and Regen, has 50% resistance to most elements (Except Fig, which it's very weak to), can dispel Haste and shields like Karnos, very high physical defense, can deal Thauma damage, has HP percentage Aether attack and puts up shields on low HP. Defeating it gives Sorcerer's Soul and Scarab of Protection.
* ''VideoGame/MarioAndLuigi'':
** ''VideoGame/MarioAndLuigiBowsersInsideStory'' has several: [[spoiler:the frozen Shroob trio in Bowser's Castle, the X bosses, and Bowser X.]]
** ''VideoGame/MarioAndLuigiDreamTeam'' also has [[spoiler:the X bosses, with giant bosses now having X forms. Taking Bowser X's place is Bowser Jr.]]
** ''VideoGame/MarioAndLuigiPaperJam'', once again, brings back [[spoiler:the X bosses, but having dropped the X - same concept, but with no name. Bowser X and Bowser Jr. are succeeded by Dry Bowser]].
* ''VideoGame/MarvelAvengersAlliance'' has the Epic Bosses in certain missions, which only show up if you fight every battle and complete every deploy (which often require spending rare Command Points to recruit specific heroes) in that mission. The bosses offer stronger weapons and gadgets and higher chances of winning more Command Points as prizes for defeating them, compared to normal bosses.
* In the ''VideoGame/MegaManBattleNetwork'' series, there is so much extra content and so many bonus bosses that the time taken to defeat them is longer than the main story line. In all of them, however, you face Bass/Forte. Unlike other continuities, here he is a god-like badass.
* ''VideoGame/MegaManStarForce'':
** Usually there's a secret area after beating the FinalBoss where you have to fight upgraded forms of each boss in the game, followed by an all-new secret boss. After doing that, the storyline's final boss is upgraded, with it being the truly strongest boss in the game. The only exception to this is the second game, where after beating the upgraded final boss, you fight [[spoiler:an upgraded Rogue after the credits finish.]]
** You can also engage a number of repeatable bonus bosses and random people who can Wave Change in ''2''. These include second shots at the storyline bosses to get their Mega cards, plus farmable bosses like Kung Foo Kyd, Gemini Spark, and Cancer Bubble.
** The third game has a rather unusual take on this with the Omega versions of the bosses, as they can rarely appear virtually anywhere in the game, and also at any point in the story, even before you've fought their regular versions. It's entirely possible to run into one of them ''right after the gameplay tutorial'', despite even weakest of them being far stronger then the final boss. Fortunately, the game is nice enough to not give you a game over for losing to them and also alerts you of their presence by changing the music in the area to a very ominous tune.
* ''VideoGame/MegaManXCommandMission,'' meanwhile, had two Bonus Bosses plus another set of nine. Rafflesian and Duckbill Mole gave X, Zero, and Axl new abilities that were useful in what remained of the game by that point. Ninetails and the preceding eight Tails Clan members, on the other hand, who were definitively even more this trope, could only be fought ''after'' beating the final boss, making the rewards for beating ''them'' [[BraggingRightsReward worthless.]]
* ''VideoGame/MonsterHunter'' has several examples, mostly reserved for multiplayer (whether local, online or both):
** The four-legged Elder Dragons (not to be mistaken with the two-legged wyverns) in most games, as well as Kirin the lightning unicorn. Most of them only appear in the highest-tier quests.
** In ''Freedom'', Yian Garuga is unlocked after hunting 10 Yian Kut-Ku. Its quest is rated with six stars (the highest grade), and it's ill-advised to challenge it until you have a decent postgame gear. In ''Monster Hunter 2'', it can only be unlocked via OldSaveBonus by connecting both games through an USB.
** In ''Freedom 2'' and ''Portable 3rd'', Gold Rathian and Silver Rathalos are unlocked by killing or capturing a combined total of 100 large Wyverns (also including Leviathans in the latter game). Note that ''Freedom Unite'' averts this trope with them, since their respective quests are mandatory in order to unlock the G Rank chapters. From ''3 Ultimate'' onwards, they're available as soon as you reach the highest-tier quest chapter, thus are demoted to merely [[SkippableBoss skippable monsters]].
** In ''Portable 3rd'', Akantor and Ukanlos ([[LegacyBossBattle originally the respective final bosses of]] ''Freedom 2'' and ''Freedom Unite'') can be fought after completing all single-monster quests in the prior high rank quests, while Alatreon (of ''Tri'' fame, [[LegacyBossBattle also its online final boss]]) is unlocked upon completion of all DualBoss monster quests.
** In ''3 Ultimate'', Hallowed Jhen Mohran is only accessible after the player slays or captures every single large monster (including previous Elder Dragons like regular Jhen Mohran and Alatreon) except Savage Deviljho, Lucent Nargacuga and Abyssal Lagiacrus (which happen to be Bonus Bosses on their own; as Savage Deviljho can only be fought in quests with unstable environments or alternatively through a DLC quest, Lucent Nargacuga is unlocked after reaching HR 40, and Abyssal Lagiacrus is unlocked after reaching HR 70).
** The endgame multiplayer quests of the original version of ''Monster Hunter 4'' consists mostly of souped-up versions of monsters you've previously fought, such as Akantor or Dalamadur, though it also adds the debuting Molten Tigrex (HR 50) and series classic Fatalis (HR 70). The expansion ''4 Ultimate'' repeats the trend for G Rank via the Aged Texts, having buffed familiar monsters while also adding Shah Dalamadur and Raging Brachydios. ''4 Ultimate'' also has the quests where you fight Apex versions of monsters, each of which is unlocked through a specific condition.[[note]]For the Apex Tidal Najarala, Gravios, Diablos, Tigrex and Zinogre, you have to hunt a specified combined total of specimens of the species and related subspecies in question. For the Apex Seregios and Rajang, you have to decipher the third and sixth Aged Texts respectively. For Apex Deviljho, you have to clear any of the previous Apex monster quests and accept the Deviljho Arena challenge in the Assembly[[/note]]
** ''Generations'' has the twelve Deviants, monster specimens that have survived numerous battles with Hunters and other monsters and have developed unique and deadly traits. All of them are optional and can only be fought through a unique series of quests. Hunters must spend special permits to post these quests because of how dangerous the Deviants are. Indeed they are, as the first, [[BearsAreBadNews Redhelm Arzuros]], is a notorious WakeUpCallBoss, and the rest go up from there. The expansion ''Generations Ultimate'' adds six more, including the Bloodbath Diablos, who can only be fought after hunting the other five new Deviants at least once and defeating the final boss. ''GU'' also has the Extra Special Permit Quests at the end of each Deviant's quest chain, which feature a Deviant with health, attack, and resistance buffed UpToEleven, require HR 100 to join, and have no supplies provided. EX Deviants are not required to defeat to max out Deviant weapons nor earn achievements, but doing so rewards a shiny color palette, Guild Card titles and special icons, and unlocks the ability to fuse Deviant armor.
** ''[[VideoGame/MonsterHunterWorld World]]'' has the monsters added after the game's release through free title updates: Deviljho, Kulve Taroth, Lunastra, [[Franchise/FinalFantasy Behemoth]], [[Franchise/TheWitcher Leshen]], Rajang, Stygian Zinogre, Safi'jiiva, Raging Brachydios, Furious Rajang, Alatreon, Frostfang Barioth and Fatalis. With the exception of Deviljho, who can be encountered randomly partway into High Rank, they can only be fought after defeating the final boss and during their respective questlines. Additionally, there are Arch-Tempered Elder Dragons, souped-up event-exclusive Elder Dragons with increased strength and sometimes new attacks and behavior that require HR 50 to fight, attainable only in the postgame.
* ''VideoGame/MonsterRancher Advance 2'' features Ragnarok, a wandering special Dragon who only appears after beating the final boss. He will only appear to fight you once a year, and only if you have a specific kind of monster on your farm. If you're not prepared to fight him on the week he comes to visit, too bad for you! His stats are extremely high (especially considering when your monster can first fight him), and he's tough.
* ''VideoGame/Mother3'' features several. First there is Lord Passion, who carries Duster's [[InfinityPlusOneSword Infinity Plus One Shoes]], Lil Miss Marshmallow guards a decent weapon for that point of the game, and the King Statue is just there for experience and is ridiculously easy if you know what to do.
* The Gundam RPG ''VideoGame/MSSagaANewDawn'' has Ultima Gundam and Omega Gundam, made from a mix of parts from ''Anime/MobileFighterGGundam'' and ''Anime/MobileSuitGundamWing'' mecha respectively. Their names are obvious {{homage}}s to ''VideoGame/FinalFantasy'''s perennial Bonus Boss pair, Ultima Weapon and Omega Weapon.
* ''[[Franchise/{{Naruto}} Naruto: Path Of The Ninja 2]]'' has the Kumite Dojo, which has many bonus bosses.
* A lot of bosses in any of the ''VideoGame/{{Neptunia}}'' games will be this trope. The strongest in ''VideoGame/HyperdimensionNeptuniaMk2'' is Delphinus without the DLC while a lot of people have a hard time against Gargoyle in ''VideoGame/HyperdimensionNeptuniaV''.
* ''VideoGame/NeverwinterNights2'':
** Tholapsyx the red dragon, thanks to her size and fire attack; buffing the entire party (preferably with Energy Immunity: Fire and Stoneskin) and micromanaging spellbooks is almost mandatory, as opposed to the final bosses, whom you can just whack with sheer force if the party is well-equipped. The reward is 200,000 gold for your keep plus an insane amount of loot, including a cool weapon for paladins and clerics who bothered to take a certain quest in the keep.
** ''[[ExpansionPack Mask of the Betrayer]]'' has its own bonus boss, a seemingly harmless badger spirit that turns into a Gigantic Angry Badger of One-hit-kill Doom if you manage to anger it. Killing it nets one one of the only items in the game to grant permanent haste status (barring the time-consuming item crafting).
** Also in ''Mask of the Betrayer'', if [[MindHive One of Many]] is in your party when you meet the dead god Myrkul, they'll ask if they can eat the god's remains. Unfortunately, rather than eating souls outright like the PlayerCharacter's curse, One of Many adds consumed souls to its collective. Thus HilarityEnsues when [[AssimilationBackfire Myrkul overpowers One of Many and takes over]].
** In ''Storm of Zehir'', you can encounter One of Many on the world map, who will probably be impossible to beat the fist time you encounter it (you're thankfully not forced into a fight with it). However, due to the WideOpenSandbox nature of the game later on, you can return and fight it once you're sufficiently leveled. Beating it will earn you the Imarskarcana, a helmet with good spell resistance, the ability to summon a demon once per day and a few other perks. If you don't want to fight it, you also have the option to feed it your companions for experience points.
* ''[[VideoGame/NocturneRPGMaker Nocturne: Rebirth]]'' has a bonus WolfpackBoss consisting of three characters from another UsefulNotes/RPGMaker game, ''Cross of the World''. After beating them once, they'll be strengthened to match a maxed-level party.
* ''VideoGame/OctopathTraveler'' has four shrines in the four corners of the world, where you can gain access to four advanced hero classes by proving your worth to the gods that guard them, along with a number of strong bosses findable by exploring caves and dungeons unrelated to the main plotlines. And in a very amusing twist, after beating all eight main scenarios then finding and fulfilling a newly unlocked chain of sidequests, you unlock the toughest challenge in the game: [[spoiler:the TrueFinalBoss linking all plotlines together, Galdera the Dark God. Looks like the simplest way to fix the "secret bonus boss is stronger than the final boss for no reason" problem is to make them one and the same.]]
* Tyrant in ''VideoGame/{{Opoona}}''. He can actually be fought surprisingly early on, before the game's halfway point, and defeating him is required to [[RelationshipValues raise your friendship]] with a few [=NPC=]s. However, taking him on so early and ''surviving'' is another matter entirely.
* ''VideoGame/PaperMario'':
** ''VideoGame/PaperMario64'':
*** Bloopers who shows up every time you find a new shortcut in the sewer (though the last one is mandatory). Kent C. Koopa also blocks a road and makes you pay to pass; beating him lets you pass for free. Then there is a Dojo, where you can fight for bragging rights. The final blooper, Kent C., and the Dojo Master could all give Bowser a run for his money if he didn't have the Star Rod.
*** There's also the [[BossInMooksClothing Anti Guy]], found guarding a chest in a dungeon halfway through the game and with HP and attack roughly on par with Bowser's penultimate form. He can be beaten straight-up, or you can exploit his SweetTooth to bribe your way to the chest's contents.
*** In Chapter 8, if you flunk a quiz from one of the Bowser-faced stone doors, your punishment will be a NoHoldsBarredBeatdown against ''three'' Anti Guys. Easily the most difficult fight in the game, as Mario will initially be taking in the ballpark of 25-30 damage a turn with (unlike all the above bosses) no way to cheese your way out of it.
** ''VideoGame/PaperMarioTheThousandYearDoor'':
*** Bonetail gives the game's final boss a run for its money (which is lampshaded by [[MetaGuy Goombella]]) and requires going through a dungeon with 90 consecutive battles (99 floors with a "breather" every 10) to reach him. He is a bit easier than the final boss, as you'll probably be better equipped and levelled by the time you reach him, and his attacks aren't as complex to deal with -- he just has enormous attack power and endurance, and getting to him is a massive two hour-long ordeal.
*** Atomic Boo, fought in Creepy Steeple if you enter the main hall and take the Spin Hammer attack to the swarms of Boos enough times. He isn't particularly hard, but knowing he even exists is a bit of a GuideDangIt.
** ''VideoGame/SuperPaperMario'': [[spoiler:The first of the three bonus bosses is really another version of the game's first boss. To even face the second boss, you have to clear a dungeon filled with even stronger enemies that are all pitch black, making distinguishing subtypes near impossible without Tippi/Tiptron until it's too late. '''''Twice.''''' The third is the 100th Sammer Guy, End Boss, the only one of them who cannot be fought until the postgame.]]
* Even an RPG that is stripped down to its bare mechanics also has one. ''VideoGame/{{Parameters}}'' has the bottom rectangle (previously the second-strongest enemy in the game), which turns into a 9999 hp opponent with high defence and attack after beating the FinalBoss. Thankfully, it isn't really ''that'' difficult so long as you have enough life regeneration, but it does get tedious as it regenerates health quickly and can take a ton of punishment.
* ''VideoGame/ParasiteEve'' had a few in the [[BonusDungeon Chrysler Building]]. While most of the bosses are color swaps of the storyline bosses, the giant cockroach and giant bee were exclusive to the building. [[spoiler:The original Eve is at the very top of the building, and defeating her gets you a different ending.]]
* ''VideoGame/PillarsOfEternity'' has the Master Below: [[spoiler:a giant GreenRocks-laced dragon]] residing at the lowest level of the Endless Paths of Od Nua--itself a {{Marathon|Level}} BrutalBonusLevel. Later patches and expansions added separate encounters with Concelhaut and Llengrath, two of the most powerful mages in the world. Llengrath is accompanied by two dragons, making it one of the most difficult battles in the game.
* ''Franchise/{{Pokemon}}'' has several, usually optional Legendary Pokémon:
** ''VideoGame/PokemonRedAndBlue'': You can find Articuno in the Seafoam Islands, Zapdos in the Power Plant, and Moltres on Victory Road. Mewtwo can be found in Cerulean Cave after you become the Champion. The use of cheats also enables the player to battle ''Professor Oak'' in the original ''Red/Blue'' versions, with a team of higher levels than the Champion. Some fans speculate that he was supposed to be a TrueFinalBoss and got removed from the storyline, [[DummiedOut but the producers forgot to remove his battle data]], since Agatha of the [[BossRush Elite Four]] states that he is a RetiredBadass. Sadly, he didn't get any battle data in the remakes ''[[VideoGameRemake FireRed/LeafGreen]]''. They did add one more in ''[=FireRed=]'' and ''[=LeafGreen=]'', though: once you've obtained the National Dex, one of Johto's legendary beasts will begin roaming for you to capture - whichever one has a type advantage against your starter (Entei for Bulbasaur, Suicune for Charmander, and Raikou for Squirtle).
** ''VideoGame/PokemonGoldAndSilver'':
*** In the first Generation II games and their remakes, the legendary that's not your version mascot counts as a Bonus Boss; in ''Crystal'', both Ho-Oh and Lugia also count, with Lugia being available only by talking to a man in Pewter City and Ho-Oh only being available by catching the legendary beasts. All three and their remakes also feature Red, the player character from ''VideoGame/PokemonRedAndBlue'', as either this or the TrueFinalBoss, depending on how you look at it. He's very tough, with all of his Pokemon over level 70. You have to massively level grind after the main game or transfer Pokemon from other games to stand a chance against him.
*** ''[[VideoGameRemake HeartGold and SoulSilver]]'' have a boss Trainer that can only be fought by having a Celebi: [[spoiler:Giovanni]]. This Trainer isn't very difficult, however, and mainly serves to tie up some loose story ends. They also add more Legendaries; once you've earned the National Dex, you'll be able to find Latios (SS) or Latias (HG) after visiting the Fan Club in Vermilion City[[labelnote:*]]If you have the event-only Enigma Stone, you can fight the other Eon Pokémon in Pewter City[[/labelnote]]; once you've beaten all sixteen Gyms, you can challenge the four Kanto Legendaries; and once you've beaten Red, you'll have completed the hardest prerequisite to battle Groudon for SS and Kyogre for HG, and Rayquaza if you have both in the same game.
*** The [[GameMod ROM hacks]] [=SacredGold=] and [=StormSilver=] come with a number of bonus bosses. First, after completing the game, the player may face the player character they didn't pick. RecurringBoss Eusine allows the player to have a rematch with him. [[VideoGame/PokemonRubyAndSapphire Steven]] appears to ask the player for a battle, as does [[VideoGame/PokemonDiamondAndPearl Cynthia]]. After capturing Mewtwo, the player may return to his location, and face off with [[TheRival Silver]], who uses a team of three OlympusMons, in reference to ''VideoGame/PokemonStadium 2''. Lastly, should the player [[GottaCatchEmAll Catch Em All]], then they may head to the Sinjoh Ruins, and battle with [[PhysicalGod Arceus]].
** ''VideoGame/PokemonRubyAndSapphire'' and their remakes (and ''Emerald'') have the legendary titans Regirock, Regice and Registeel. After defeating the Champion, one of the Eon Pokémon (Latios for ''Ruby'', Latias for ''Sapphire'') and Rayquaza can be caught. Through event-exclusive items, Lugia, Ho-oh, the other Eon Pokémon, and Deoxys can be fought. Mew can also be found this way in ''Emerald''.
** In ''Emerald'', Rayquaza can be captured ''before'' you take on the Elite Four (and Groudon and Kyogre take its place as Bonus Bosses). You can also choose which Eon Pokémon you encounter after entering the Hall of Fame. A traditional example appears in the form of Steven, who turns from FinalBoss in ''Ruby/Sapphire'' to Bonus Boss in ''Emerald'', having stepped down from his position as Champion. After entering the Hall of Fame, you'll find him in a secluded cave in Meteor Falls with a team identical to the one he has in ''Ruby/Sapphire'', except ''twenty levels higher''. The seven Frontier Brains at the Battle Frontier also count, as they are only available after you beat the Champion. Additionally, in ''[[VideoGameRemake Omega Ruby/Alpha Sapphire]]'', you can battle ''all of the other Legendaries from Generations II, IV, and V,'' along with the previously [[SecretCharacter Mythical]] Deoxys.
** ''VideoGame/PokemonDiamondAndPearl'' (and ''Platinum'') have Heatran, Giratina, Cresselia, and Regigigas; four legendaries that can only be encountered after you've beaten the main storyline and obtained the [[GottaCatchEmAll National Dex]]. ''Platinum'' (noticing a trend here?) adds even more; the three Legendary Birds of Kanto after you've earned the National Dex and, as Giratina is the version mascot and therefore encountered as part of the story, both Dialga and Palkia become Bonus Bosses if you visit Spear Pillar with their orbs. Also, Regigigas's status is tarnished somewhat, as in ''Platinum'', it's dropped to Level 1. Also, through now legitimately unobtainable event items, players can fight the Mythical Pokémon Darkrai and Shaymin. In ''Platinum'', an event Regigigas can unlock areas where the Regi trio can be battled and caught. Arceus can also be found in the Hall of Origin, but the item needed to access it [[DummiedOut was never officially released]].
** ''VideoGame/PokemonBlackAndWhite'' have [[spoiler:Cynthia]] as their bonus boss, as well as [[CreatorCameo one of the game's developers from Game Freak, Inc.]]. In addition, [[spoiler:Alder, the League Champion, previously TheUnfought due to story complications]], can also be challenged by challenging the Elite Four to a rematch. The Subway Bosses of Unova's Battle Subway, can be considered this after one defeats the Champion. As for Legendary Pokémon, Cobalion, Terrakion and Virizion can be found through a sidequest, and post-Elite Four, Landorus can be battled if the player has a Tornadus and a Thundurus, and Kyurem can be fought in the Giant Chasm. An event item also lets you travel to Liberty Island to battle Victini.
** ''VideoGame/PokemonBlack2AndWhite2'' goes UpToEleven on this one, letting you battle nearly '''all''' of the previous Gym Leaders from Generations I-V, from Brock to Drayden, in the Pokemon World Tournament or PWT. If you manage to conquer the regional tourneys and the World Leaders tournament, you get to fight all of the previous Champions (minus Iris) in the Champions League. Also, there's Colress, the Shadow Triad, the Striaton Trio (Cilan, Chili, Cress) in a Multi Battle, now RetiredBadass Alder, his grandson Benga, the [[CreatorCameo GameFREAK]] trainers, and under the right conditions, [[spoiler:Cheren (with his original team), Bianca, and '''N''']]. There are plenty of powerful trainers to battle for the postgame. The legendaries are no slouch either, with the Regi quartet, the Sinnoh lake guardians, the Eon Pokémon, Cresselia, and Heatran showing up. You can also fight and catch [[spoiler:N's legendary dragon]] and Kyurem, who can't be captured during the main story.
** ''VideoGame/PokemonXAndY'' doesn't have as many of these bosses as the previous generation did. For Legendary Pokemon, there's one of Kanto's Legendary Birds (which one you'll face depends on the starter you picked), Zygarde, and Mewtwo. As for trainers, it is possible to challenge [[TheRival Calem/Serena]] to a rematch postgame, and [[spoiler:going through Looker's missions has you battle Essentia ''four times in a row'']].
** ''VideoGame/PokemonMysteryDungeon'' games have various Legendary Pokémon, and most Legendary Pokémon that have no relation to the plot in the second set of ''VideoGame/PokemonMysteryDungeon'' games.
** ''VideoGame/PokemonSunAndMoon'' has the [[spoiler:Looker sidequests,]] which has you catch all five Ultra Beasts, some of which are different depending on your version. This part of the postgame also has you fighting [[spoiler:Anabel, Mina, and Nanu]]. This and the ''Ultra'' sequels are also the only games in the series where the character must defend their Champion status every time they fight the Elite Four, rematching various trainers encountered throughout the game. Speaking of, the Battle Tree also has you facing off against various trainers from previous generations and those encountered throughout the game. You can also catch all four of the Guardian Deities. Once you complete the [[spoiler:Looker sidequests, you can also catch Necrozma in Ten Carat Hill.]] Some new battles are possible in some locations, such as [[spoiler:Guzma]] in Hau'oli City, [[spoiler:Faba]] in Aether Paradise, and [[spoiler:Principal Asuka]] in the Trainer's School. Finally, after you beat all of the [[spoiler:Eevee Users, you can fight Eevee User Kagetora.]]
** ''[[VideoGame/PokemonUltraSunAndUltraMoon Ultra Sun and Moon]]'' expands on this. First, the Looker sidequests are replaced with Episode RR, which features Team Rainbow Rocket, a team built up from the villain teams of the first six generations, meaning that all their leaders can be fought, with them using the Legendaries that were central to their plans in their original games. The matches where the player defends their Champion title are also altered, with two trainers being replaced, while the two rival characters have much stronger teams this time. The player can also revisit the first trial, but with the Totem Pokemon at a much higher level. The player also gets a chance to catch a new Ultra Beast during the post-game, with the original Ultra Beasts being found in their own dimensions. The dimensional travel also lets the player battle all the Legendaries of previous generation, similar to ORAS.
* ''VideoGame/RakenzarnTales'' has a feature known as the Ultra Boss. You need a specific party member in your line-up when fighting a specific boss under certain conditions -- usually having cleared a minimum number of quests. They're a pretty clear step up, but winning gets you a stat boost, bonus stats and a new piece of equipment that grants a party member exclusive move.
* ''VideoGame/ResonanceOfFate'' pits you up against [[spoiler:Sullivan and Rebecca]] at the end of [[BonusDungeon Neverland]]. Unlike many examples on this page, they are generally considered pushovers, especially compared to what you fought to get to them.
* ''VideoGame/RivieraThePromisedLand'' has Hades, the boss who only appear in the extra content section after you complete the game and obtained the Key to Hell from the Zombie Dragon in chapter 6. His Breakout does heavy damage, but he only attack once every 3 of your each character's turns (estimated), so if you keep healing yourself with elixer and attack him, he's a pushover. Of course, the final boss can has its HP brought down by 53% with [[InfinityPlusOneSword Fanelia]]...
* ''VideoGame/{{Robopon}}'' has a couple. In the original, you can rematch the first six Legends in Zero Tower post-credits. The second game has several, including Rena's restored-to-youth mother, the younger version of Nick D., the Robopon in Delica Castle's basement, and the W-King.
* ''VideoGame/SacredEarthPromise'' has [[spoiler:an unnamed shadowy version of Isole]] in Icefall Labyrinth, who is on a similar level of difficulty as the FinalBoss, Forneus.
* In the ''VideoGame/{{SaGa|RPG}}'' series, most of the '''game''' is optional, including many of the bosses. ''VideoGame/SagaFrontier'' does have a few optional bosses who are '''particularly''' difficult, including the Earth Dragon in the Bio Research Lab, and [[Main/TheComputerIsACheatingBastard cheating bastard]] Jotnar, who likes to employ his most powerful attack four consecutive times on his second turn.
* ''VideoGame/SailorMoonAnotherStory'' has [[spoiler:Esmeraude in the fourth chapter]]. Beating said boss gets you [[spoiler:a second Red Pupil]].
* ''VideoGame/SandsOfDestruction'' features Dark Kyrie, the protagonist's doppelganger spawned from his fear and doubt. He's entirely optional and can only be accessed by getting back inside the Temple of Light after it's been darkened (which [[GuideDangIt wasn't easy the first time]] and isn't any easier the second), but he drops his InfinityPlusOneSword, the Destruct Blade.
* ''Franchise/ShinMegamiTensei'': Creator/{{Atlus}} has loved making [[ThatOneBoss these noble fellas]] to rain Megidolaons upon us since the early 90's:
** ''VideoGame/DigitalDevilSaga'':
*** The [[spoiler:Demi-Fiend]] battle in the first one, one of the hardest bosses in the history of {{JRPG}}s, if not ''the'' hardest boss. Not only will he instantly kill you in the first turn if you have a "forbidden" move set (read: any passive or castable move intended to null, absorb or repel enemy attacks), but the strategy required to defeat him requires a very specific use of one usually worthless skill that you would ''never'' use in the main game (to wit, the Null Sleep skill, which nulls all damage one would receive while asleep). How anyone could figure this out without the use of a strategy guide is a mystery for the ages. Beating him unlocks an useful accessory that you can find midgame through the sequel that boosts all stats by 10. And even then, if you do manage to get him down to half health, his High Pixie will fully heal him. If you kill all of his demon companions, he'll insta-kill you. If you go in with any protective moves, he'll insta-kill you. Hell, even with the correct strategy, if you take too long to kill him, he'll just get bored and insta-kill you anyway. To add insult to injury, his battle music is the ''regular Nocturne battle music'', so he may be an uber hard bonus fight to you, but you're nothing more than ''a random encounter'' to him.
*** [[spoiler:Satan]] in the sequel is likewise enormously difficult, if a lot less so than the [[spoiler:Demi-Fiend]]; you require to continuously cast Charge to boost all your stats to max so [[spoiler:Satan]] won't cast God's Breath, his insta-kill move. If you did so, good, he'll only cast Dekaja and put you back at square one. Hurt him enough and take too long and he will cast Diarahan, putting himself back at full health. Anyway, even without their instant kill skills, both are beastly difficult -- you ''need'' to cap out your major stats to even have a fighting chance, and ''then'' there's the actual strategy involved... which simply fails half the time due to bad luck. You also cannot fight [[spoiler:Satan]] on Normal Mode; you explicitly ''have to be'' playing on Hard Mode or your team will be too fearful to even enter his room.
*** TheFourGods: Each appears in a different sector in the first game, each representing a specific element. Avoid repelling their elemental attacks or hitting them with their respective elements and they will go down fairly easily.
*** Huang Long: Appears high in the Karma Temple after killing TheFourGods. Hits like a truck with the Almighty-type Celestial Ray, which also slaps you with any ailment he wants. Has tons of HP and can cycle through several forms to make the task of damaging him harder. Still not as hard as the [[spoiler:Demi-Fiend]].
*** Beelzebub's two forms: Baal Zabul appears in Svadhisthana's underbelly once you unlock it with the Red Key. While he ''is'' somewhat strong, he's really nothing to be worried about. Beelzebub proper appears after Baal Zabul's defeat in the Manipura Waterways, and comes back with a vengeance, packing the lethal ''Death Flies'' move, which will kill anything not protected against Dark attacks with 100% effectiveness. Even if your charaters ''are'' protected, it will hit with a horribly strong Almighty-type attack.
*** Orochi is the last obstacle in the path to the Red Ring, required for another boss. He has ''eight'' actions on his turn, can exploit elemental affinities and Criticals with Ice and Lightning attacks, abuse Makakaja and Megidolaon, and has a crapload of resistances. However, he has pathetically small MP for a boss, and will try to restore his tanks with yours. With Null Mute, he turns into a joke after a few turns.
*** Metatron fights you after you enter Ajna with the Red Ring and killed TheFourGods. He likes to abuse Makakaja, Revelation, and Fire of Sinai, which can hit several times for Almighty damage with the possibility of instant death.
*** King Frost appears at Coordinate 136 after the defeat of Mick the Slug. Finish the minigame of "find the key" and King Frost will appear at the Princess's Bedchamber. He spams Cocytus, which will almost always freeze, and summons overleveled Jack Frosts to pound you.
*** In the second game, there are fights against the Four Archangels, Shiva, Vishnu, Jack Frost and Seth. The Shiva and Vishnu fights also require you to find a special item for each, from Parvati for Shiva and Narasimha for Vishnu. The pathway to Seth is blocked off until you defeat Shiva and Vishnu and Seth himself blocks the way to [[spoiler:Satan]].
** ''VideoGame/ShinMegamiTenseiI'' and ''VideoGame/RaidouKuzunohaVsTheSoullessArmy'' has Beelzebub. ''Soulless'' is particularly vicious as he requires three items to be fought, all of which have to be acquired through ZergRush battles with 100 enemies each; these will tend to be DemonicSpiders. Then, he will be fought amidst ''another'' ZergRush. Pray none of your healing demons get Charmed, as he will use and abuse any attacks which can inflict said ailment to jack up his health.
** ''VideoGame/ShinMegamiTenseiStrangeJourney'' has the NGP-exclusive [[PowerLimiter Alilat]] and [[PhysicalGod Demiurge]]. Alilat has the game-breaking combo of high Magic stat, Mind Charge, and Megidolaon-a nigh-guaranteed TotalPartyKill. Demiurge is a BarrierChangeBoss, has Big Bang which deals even more raw damage than Megidolaon, regularly heals himself with Diarama, and has a ton of HP. Additionally, he's fast enough to dodge most of you attacks and has all of the deadliest elemental spells.
*** The UpdatedRerelease, ''Strange Journey Redux'', introduces a quartet of even stronger bosses under the command of Louisa Ferre, available only on a NewGamePlus. Belial, Lucifuge, Nebiros, and Beelzebub are all capable of shuffling their weakness and obscuring their analysis data after you've just exploited it for free Co-Op damage. They also have very high stats across the board, and if taken too long to defeat, will bombard your party with Doomsday which is almost guaranteed to kill. If you consider the Womb of Grief a BonusDungeon (as it's not mandatory for the main plot, but does unlock the new endings) then its associated bosses qualify for this trope.
** ''VideoGame/RaidouKuzunohaVsKingAbaddon'' has Masakado and Lucifer.
** ''VideoGame/ShinMegamiTenseiI'' has Beelzebub as the ultimate Bonus Boss, but there were others, such as the series's first three Fiends: Daisoujou, David, and Pale Rider.
** ''VideoGame/ShinMegamiTenseiII'' brings back Beelzebub as the ultimate boss. There are also the Fiends, of which there are five this time: Alice, Hell Biker, Ghost Q, the Sage of Time, and Matador.
** ''VideoGame/ShinMegamiTenseiIIINocturne'' plays around with this. The bosses of the UpdatedRerelease are required for the new ending, but many consider them Bonus Bosses as well. These include all of the Fiends (save Matador and the first fight with [[VideoGame/DevilMayCry Dante]]/[[VideoGame/RaidouKuzunohaVSTheSoullessArmy Raidou]] [[VideoGame/RaidouKuzunohaVsKingAbaddon Kuzunoha XIV]], who is required), Beelzebub, and Metatron. Also present but unconnected to this questline are the Buddhist Four Heavenly Kings, who reside at Bandou Shrine, have maxed stats and the most powerful attacks of their respective elements, and guard the game's most powerful [[AmplifierArtifact Magatama]].
** ''VideoGame/ShinMegamiTenseiIV'' has both the Fiends (Matador is one example) and the DLC Bosses ([[spoiler:The Four Archangels, Ancient of Days, Sanat, and Masakado.]])
*** The game also has a plethora of bosses that can only be fought in their respective challenge quests. While the majority of them pale in comparison to the monsters already listed (the main exceptions are Beelzebub ([[OnceAnEpisode of course]]) and the New Game + exclusive Astaroth), they still count since most challenge quests are optional. Other than the aforementioned opponents, there's one particularly strong Bonus Boss for each route (though they don't compare to the Fiends, DLC Bosses, Beelzebub, and Astaroth, they're still stronger than other Challenge Quest bosses): [[spoiler:Mastema for Law, Demiurge for Chaos, and Shiva for Neutral, with the first two coming form Challenge Quests and the last being the Terminal Guardian's final battle]].
*** Special mention must go to the Fiends. Seven of these Fiends (Matador from above being one of them) can only be found in certain locations and the chance of actually encountering them is very low (1 out of 256). Each one has at least five Press Turn icons, will always get the first strike, and will spam Antichthon (massive Almighty damage and all stats lowered) or similar skills if they cannot safely attack you or your demons with their preferred attacks. Defeating them will unlock them for special fusion, and often, a wonderful reward, including some of the game's best equipment.
** ''VideoGame/ShinMegamiTenseiIVApocalypse'' brings back the Fiends along with [[spoiler:En no Ozuno from the first game]]. DLC adds [[spoiler:Mephisto, Cleopatra, and a demonic Hope and Hugo]]. The final DLC makes the ultimate opponent [[spoiler:Stephen, who fights against every numbered SMT protagonist at once]].
** ''Franchise/{{Persona}}'':
*** ''VideoGame/Persona2'' was the sub-series's first entry in this list with Philemon's brutal bonus battle on his EX Dungeon. Notably, he's the ''only'' enemy, let alone boss, in the entire game who is immune to the Fusion Skill Armageddon, which, if used, can one-shot even the final boss. Try to use it on him, and he'll hit back with Armageddon R, wiping your party without fail and leading to a game over.
*** ''VideoGame/Persona3'' has Velvet Room attendant Elizabeth. She can only be fought on the second playthrough by accepting her 55th request and going to the top of Monad. She seems to be nothing more than a thin blonde girl dressed like a bellhop, but she is the most powerful foe in the game, can only be fought one-on-one (she'll kill any other party members right away), gets to attack twice every turn (where you can only attack once), has multiple personas and powerful attacks, and heals herself completely when at low health. Even worse, if any of her attacks are nullified, reflected, or absorbed (which they invariably will be, considering her attack rate and huge range of attacks), she goes berserk and spams a 9999-damage attack (out of max possible HP of 999) nonstop until you die. Amusingly enough, the UpdatedRerelease version of the game features an upgraded version of your starter Persona which seems to be tailor-made to fight her, as it resists every type of attack, giving you a good overall defense against anything she tosses out and avoiding driving her berserk.
*** While nowhere near as insane as Elizabeth, the Reaper that can be fought in both version of P3 is no slouch when it comes to making a normal player tear their hair out. It's fond of casting spells that hit the whole party for 700-800 damage and going insane on unblockable "almighty" spells if the player sets up reflecting items. This one is more infuriating to the average player due to the fact that he appears when the player spends too long in Tartarus, the game's central randomly generated dungeon. It makes a return in ''VideoGame/Persona4'', and is found while opening a chest (the game warns you about it and gives you two chances to back out). It returns again in ''VideoGame/Persona5'', where it'll appear if you stay too long on one level of Mementos, though this time around it's possible for it to [[WorfHadTheFlu catch the flu]] during certain days, severely weakening it.
*** ''Persona 3 Portable'' allows you to fight Velvet Room attendant (and Elizabeth's brother) Theodore if you make the proper choice early on in the game (it's not dependent on gender). However, it cranks things up to 11 with the Vision Quest, which not only contains more difficult versions of the Arcana Shadows, but also allows you to fight [[spoiler:Margaret! Yes, the one in the next example. You can still use your full party, but that doesn't make things any easier...]]
*** ''VideoGame/Persona4'' continues the tradition with Velvet Room attendant (and Elizabeth and Theodore's big sister) Margaret, who is unlocked by reaching the True Ending after clearing Margaret's Social Link and killing the six other optional bosses (see below). While you can bring in party members and she won't (immediately) wipe them, she's just as frustrating. Nice changes include only healing once. She'll still 9999 Megidolaon you if you bring in a forbidden item, and do so on you every 50 turns. She'll also exploit 1 More relentlessly if you give her the chance in the pattern. She won't kill you if you reflect or nullify her spells, but she shifts her weaknesses around so that she heals if you reflect a spell at her. ''Golden'' increases her difficulty by allowing her to go twice every turn, essentially halving the time it takes for her to use Megidolaon, as a way of offsetting the various new features that make things easier.
*** After defeating a dungeon's main boss in ''4'', a new, optional boss appears in the original's place. These tend to be [[EarlyBirdBoss a few orders of magnitude harder]]. If you fight the Contrarian King as soon as he becomes available, you will die. If you fight him after making your way through the next dungeon and bumping up a good 10 or 15 levels... you'll probably still die. His Rampage attack is overpowered enough to wipe your party in one shot, and he gives himself Fire resistance as soon as the battle starts. [[spoiler: Fire ''heals'' him. He has no actual weaknesses.]] Naturally he's the first Bonus Boss to become available, and the game will [[SchmuckBait encourage you to challenge him well before you're ready]]. The others aren't quite as difficult, and some actually have elemental weaknesses. If you defeat them, you're rewarded with a large Courage boost and a useful piece of equipment hidden in the boss room.
*** ''VideoGame/PersonaQShadowOfTheLabyrinth'' continues the tradition of having the residents of the Velvet Room be overpowered bonus bosses, though for the most part things are a bit easier. You can fight Elizabeth several times throughout the game, with her difficulty slowly increasing over time [[spoiler:and eventually, she's possessed by Zeus]]. Margaret is also an optional battle, in which [[spoiler:you fight her two on one with the protagonist you didn't pick, in order to unlock your ultimate Personas]]. However, it wouldn't be a crossover game if you didn't have a chance to fight Elizabeth, Theodore, and Margaret simultaneously. They can even do an [[CombinationAttack All-Out Attack]] every five turns, though they're more forgiving than they are in the base games.
*** ''VideoGame/Persona5'' once again continues the tradition of overpowered Velvet Room attendants with Caroline and Justine. Like the ''Persona Q'' battle against Elizabeth, Theodore, and Margret, they battle you as a team. Thus when one falls, the other will revive them, and they can do an [[CombinationAttack All-Out Attack]] when all your team is knocked down. They can also use the new Baton Pass command, making it even more imperative to make sure they don't hit any of your weaknesses.
*** ''[[UpdatedRerelease Persona 5 Royal]]'' adds a new boss fight in the Third Trimester against [[spoiler: the Twins' combined true form, Lavenza]]. Unlike the Twins, this is just a single boss, but in exchange, they utilize advanced tactics such as using buffs and debuffs and have resistances that constantly shift throughout the fight. [[spoiler: And they can still perform an All-Out Attack by splitting back into the Twins if given the chance.]]
*** ''VideoGame/PersonaQ2NewCinemaLabyrinth'', like the first game, features a fight with all the Velvet Room attendants. This time, there's four phases- Caroline and Justine fight you in the first phase, alongside Margaret in the second phase, Theodore in the third phase and Elizabeth in the fourth phase. In the lead-up to this huge fight, you get to fight each attendant (the twins are fought together) separately, one fight for each Sooty Film you collect from a Special Screening set at the final floor of each movie.
** ''VideoGame/DevilSurvivor'' holds a few bonus bosses. They appear as unique Free Battles that don't advance the clock. The ''Overclocked'' UpdatedRerelease adds a few more.
*** Ghost Q shows up on Day 2, offering treasure. If you select the correct card (it's totally random), you can complete his stage without having to defeat him, but the other cards turn into doubles of him.
*** Sage of Time shows up on Day 6, hypnotizing civilians. If any of them make it all the way to him, he'll take their souls and you get a game over. You can wake them up to get them to start heading away from him, but if a demon gets them before they get away, same result. Later on the fight, the Sage will brainwash more civilians into entering.
*** Ikusa shows up with a swarm of powerful undead on Day 4. He revives the ones you defeat, and furthermore, you have to prevent any of them from reaching a pair of escape points while you battle him, then clean up after he's gone.
*** Also in Day 5, Nebiros. He appears surrounded by a lot of Vile demons with healing capabilities, meaning he can hide behind them and hit you from afar.
*** The Fallen Morning Star, Lucifer, is the toughest boss of them all, and is also available in the base game. While insanely difficult (infinite range, level 99, etc.), beating him does give you the ability to fuse him. Most people just take advantage of the fact that Recarm gives the revived the next turn to attack, and just suicide run him. Though your strategies are moot if he manages to get Megidoladyne off a couple of times, since every cast boosts its power until the 4th/5th is LETHAL. The first already does 500-600 on everyone!
** ''VideoGame/DevilSurvivor2'' has a whole slew of these. Ghost Q and Billiken are available in the first playthrough; the rest will require a NewGamePlus at minimum. Nebiros, Belial and Alice require you to purchase the perk that lets you fight them.
*** Ghost Q shows up at a time when you only have the MC in the party--you actually can get one other character into your party before engaging him, but he won't fight you. Also, if you defeat all of the other demons on the field before finishing him off, he'll run away.
*** Billiken is a fairly standard battle, except his battle is the first one in which you can crack Holy Dance, and unless you abuse the hell out of the movement skills, he's programmed to go straight for the Pazuzu that has it and one-shot it. He can also steal money from enemies; if he manages to deplete your wallet, he can hit you with Barrage Strike, which hits for a lot of Almighty damage.
*** The Sage of Time will fight you with mid-tier demons when you're far too underleveled to be able to equip any of the heavier-hitting moves in your arsenal.
*** Lilith sics a bunch of hypnotized civilians which you have to avoid killing with immensely strong demons, ''and'' her Temptation skill will wreak havoc amongst enemy leaders. Worse, any male leaders hit by Temptation will be charmed without fail, even with Null Mystic (the Barrier Auto Skill will stop male leaders from being charmed if they have it equipped). Female leaders aren't charmed just as unfailingly, but there ''is'' a chance Lilith can charm them anyway.
*** Beelzebub is a vicious BarrierChangeBoss with a nigh-flawless defense and incredible attack, with a continuous stream of overleveled {{mook}}s.
*** As a CallBack to his boss fight in the first game, Belial will regularly hit the entire map with Gomorrah Fire, so you and your demons need to, at least, Null Fire.
*** Nebiros will appear in a gaggle of undead and continuously summon more if you kill them, and BodySurf into them if you instead choose to go after him.
*** Finally, Alice isn't as difficult as Lucifer, but she does have Belial and Nebiros fighting with her, both with their signature tricks. Alice herself can easily oneshot entire parties with ''Die For Me!'', remotely drain them to death with Vitality Drain, revive Belial and Nebiros, and speed up their turns.
*** The UpdatedRerelease, ''Record Breaker'', gives you an option to fight the Ticos. One of the biggest bummer about this fight is that they bring back the dreaded ''Megidoladyne''.
* ''VideoGame/SkiesOfArcadia''::
** The original game has some. You don't have to fight any of the giant monsters (Obispo, the Roc, the Giant Looper, and Alania). There's also [[MetalSlime Elcian]], a super Looper who appears in the Dark Rift near the end of the game, who puts up a tough fight but gives good experience and loot and can be fought multiple times, making him great for LevelGrinding. And finally, OneHundredPercentCompletion unlocks one final battle against [[spoiler:Air Pirate Vigoro]].
** The bounty bosses in ''Legends''. They are also ThatOneBoss -- because even for a bonus boss, their difficulty is sadistic.
* ''VideoGame/TheSpiritEngine2'' has a variant: the bonus boss, Urtat Underval, is fought roughly halfway through the game rather than at the end. Another variant is that you fight him twice; [[spoiler:once as a human, and once as a hulking zombie]].
* ''VideoGame/SuperMarioRPG'' has three:
** Tiny martial arts master Jinx, who you must fight three times (after defeating his apprentice, Jagger). The boss lives in Monstro Town.
** ''VideoGame/FinalFantasy'' ShoutOut Culex, a powerful magic-using entity from another dimension who attacks using four elemental crystals and is harder than the game's FinalBoss. It too lives in Monstro Town.
** There's also Mokura, a green cloud monster that appears randomly in Belome Temple and has boss music playing during his fight.
* The ROMHack ''Super Mario RPG Armageddon'' adds a ton of NintendoHard bonus bosses, including [[VideoGame/FinalFantasyIX Ozma]], [[VideoGame/FinalFantasyX Penence]], [[VideoGame/FinalFantasyXII Yiazmat]], [[VideoGame/FinalFantasyVI Goddess, the Elemental Dragons, Kaiser Dragon]],[[VideoGame/FinalFantasyIVTheAfterYears Mysterious Girl]], [[VideoGame/SuperMarioGalaxy Rosalina]], [[VideoGame/PaperMarioTheThousandYearDoor The Shadow Queen]], [[VideoGame/ChronoTrigger Magus and Schala]] (as a DualBoss), [[VideoGame/PaperMario Anti Guy, General Guy, The Master]], and the two most powerful bosses of all: [[spoiler: [[VideoGames/KingdomHearts358DaysOver2 Xion]]]] and [[spoiler: [[VideoGames/FinalFantasyVI Terra]]]].
* ''VideoGame/TalesSeries'':
** ''VideoGame/TalesOfDestiny2'':
*** The original [=PS2=] version has Lymle [[spoiler: Aileron, Kyle's cousin]] in the arena, and [[EldritchAbomination Magnadeus]] in the BonusDungeon.
*** The PSP version adds a few more, like Rutee, Philia, and Woodrow in the arena, and [[spoiler: zombie Leon]] as one of Magnadeus's minibosses.
** ''VideoGame/TalesOfSymphonia'':
*** The game had at least 6 hidden bosses [[spoiler:(Seles, Abyssion, Maxwell, three former Tales characters (Woodrow/Garr, Farah, and Meredy), and the Sword Dancer, and the Living Armor at the end of [[BrutalBonusLevel Forbidden Anamnesis]])]], the second of which gives you [[InfinityPlusOneSword weapons]] that makes the rest of the game ridiculously easy -- [[BraggingRightsReward as if it weren't already for anyone powerful enough to defeat him in the first place]].
*** During your first encounter with the Sword Dancer, you may or may not get fucked up almost immediately. His attacks are absurdly powerful in this encounter, being able to KO the '''ENTIRE PARTY''' with a ''single attack.'' Though, if Raine unlocked one of her spells, like the photon spell, then you can defeat it rather easily. The next two encounters are only moderately hard because you'll be appropriately-leveled and you'll be able to use Unison Attacks.
*** [[spoiler: Abyssion]] could give some Creator/{{Atlus}} bosses a run for their money. Because of the [[spoiler: [[ArtifactOfDoom Devil's Arms,]]]] he can [[PowerCopying mimic every character's fighting style in rapid succession]], can cast the most dangerous spells in the game with barely any delay, hits like a freight train with both magic and physical attacks, and has '''[[DamageSpongeBoss 180,000 HP,]]''' ''three times'' as much as the FinalBoss. And he only [[TurnsRed gets]] [[UpToEleven harder]] when you reduce him to half HP. Martel help you if he goes into [[SuperMode Over Limit...]] [[SarcasmMode Even better,]] he is capable of using Genis's Indignation Judgement, and, in the [=PS2=] version, he can also use Lloyd and Kratos/Zelos's final attacks as well. And finally, in the [=PS2=] version? [[TheComputerIsACheatingBastard He's immune to All-Divides.]]
*** You fight Garr, Farah, and Meredy in the coliseum. They are absurdly hard to beat, in fact, think of having to fight Lloyd, Genis, Zelos, and Presea at the same time, while they use the very same battle strategy as you do, which is what makes them so hard. But once you get rid of Farah, then Meredy and Garr are almost a piece of cake, that is assuming you have enough healing items. The best party to fight them with are Lloyd, Zelos/Kratos, and Genis. Replacing Genis with Raine is also a good idea, but her lack of offensive spells may cause the fight to drag on. It's kinda funny hearing Lloyd say "Who the hell were those guys?" after beating them.
*** The [=PS2=] Remake adds two new [[DualBoss Trio Bosses]] to the Forbidden Anamnesis: [[spoiler:Magnius, Pronyma, and Forcystus from before Pronyma became the leader of the Grand Cardinals]] and [[spoiler:Mithos, Yuan, and Kratos from 4,000 years ago]], the latter of whom demand to fight you [[DuelBoss Three-On-Three]].
** ''VideoGame/TalesOfPhantasia'' had Pluto, who gave you his summon, and Odin, who is also a DuelBoss. Apparently, he really was ''that'' Odin.
** ''VideoGame/TalesOfEternia'' had Sekundes, the summon of Time, but you didn't have to beat him to enlist his services. Maxwell and Shadow were also technically optional, but you ''did'' have to beat them. Cless gives you his bandanna and the Eternal Sword if you beat him in the Arena, and Valkyrie stands before a ''lot'' of treasure chests. Things like this make ''Eternia'' end up a very long and interesting game.
** ''VideoGame/TalesOfVesperia'':
*** The "Traitor to the Heavens" ([[spoiler:[[VideoGame/TalesOfSymphonia Kratos]] fulfilling the role of a cameo boss]]). It also has a bit of an odd case with the Radiant Winged One, [[spoiler:who, while entirely optional, if the player opts to fight him, [[TrueFinalBoss ends up as the last boss anyway]].]]
*** There are also [[spoiler:[[VideoGame/TalesOfPhantasia Dhaos]], [[VideoGame/TalesOfEternia Shizel]], [[VideoGame/TalesOfDestiny Barbatos]] (who still HATES items), and [[VideoGame/TalesOfSymphonia Kratos]]]] as bosses in the 200 Man Melee.
*** The [=PS3=] UpdatedRerelease adds several more optional bosses, such as Clint of the Hunting Blades, the Sword Dancers [[spoiler:which reward you with Flynn's normal, non-Fell Arm InfinityPlusOneSword]], and [[spoiler:the Spiral Draco, lord of the Entelexeia and possibly the most difficult boss in the entire ''VideoGame/TalesSeries'']].
*** There's also a colosseum fight where you use the four characters you currently have in your party against computer controlled versions of the other four you aren't using.
*** In addition to the already long list of bonus bosses in Vesperia, there's also Yeager's bodyguards, Gauche and Droite.
** ''VideoGame/TalesOfTheAbyss'' contains [[spoiler:Nebilim]], who tests how well you are at free running and using altered artes, Reid, Mint, Nanaly, and Philia in the colliseum, the recurring Sword Dancer, as well as [[spoiler:Arietta, Largo, Sync, Arietta in a team]] and [[spoiler:Replicantis]]in the second playthrough exclusive Abyss Replica Lab.
** ''VideoGame/TalesOfGraces'':
*** The post-game boss Solomos, as well as all the other bosses in the [[BonusDungeon Zone Cage]] and Coliseum (including [[spoiler:Veigue, Kohak/Amber, and Reala as the previous Tales cameo battle]] and [[spoiler:Poisson]]. Defeating Solomos also ''changes'' the real final boss, [[spoiler:Lambda Angelus]] into [[spoiler:Lambda Theos]]. In addition, you can re-fight your first boss; he is no longer the WarmUpBoss that he was before. You also can fight the incredibly large and strong [[AttackOfThe50FootWhatever Rockgagan]]. In the [=PS3=] version, you only really get a [[BraggingRightsReward trophy]] for defeating him - not even experience points.
*** There's also the three dragons that correspond to the 3 Giant Cryas in each country. Good luck trying to take them on before beating the final boss cause even on Normal, it's not easy.
** ''VideoGame/TalesOfXillia'' has the Golden Swordsman at the end of its BonusDungeon. He's nothing to scoff at the first time you fight him, but he gets even stronger the next few times you fight him.
** ''VideoGame/TalesOfXillia2'' has a massive number of these compared to its prequel, all available after beating the game. Defeating all of the Giganto Monsters will result in all of them reappearing as their much stronger EX versions. The bonus dungeon is populated by shadow versions of numerous past bosses, your party members, and [[spoiler:[[VideoGame/TalesOfDestiny Stahn]]]] and [[spoiler: [[VideoGame/TalesOfPhantasia Cless]]]]. The end of EX Tag Arena pits you against powerful versions of past bosses partnered with random members of your party, plus if you defeat them quickly, you'll be rewarded with a bonus fight based on who your lead character is (Most notably, in Ludger's case, a stronger version of [[spoiler:''the final boss'']] shows up). Lastly, the end of EX Team Arena pits you against the cameo team of [[spoiler:Cless, Mint, Stahn, and Rutee]] in a battle that's chaotic enough to warrant a special ending scene should you prevail.
** Also, ''VideoGame/TalesOfHearts'' bonus boss is nearly IMPOSSIBLE without use of infinite aerial combos or cheats.
* The Black Rabite from ''VideoGame/TrialsOfMana'' looks like a black version of the cute and weak Rabite enemies from the beginning of the game, but is the exact opposite of weak. [[KillerRabbit Evil in its cutest form!]]
* ''VideoGame/UncommonTime'' has one at the end of each BonusDungeon: [[spoiler:Altair]] at the end of Aubrey's Uncommon Time, and [[spoiler:Arietta]] at the end of Arietta's.
* ''VideoGame/{{Undertale}}'':
** Glyde, who only appears in the room with the door in Snowdin Woods, with a very low encounter rate.
** So Sorry, who appears in Hotland after unlocking all of the elevators near Sans' hot dog stand, but only at 8pm on October 10th.
** The Nintendo Switch version adds an optional boss fight with [[spoiler:Mad Mew Mew]], [[spoiler:a life-sized Mew Mew Kissy Cutie figurine possessed by the Mad Dummy.]]
** In the follow-up/{{Elseworld}} game ''VideoGame/{{Deltarune}}'', you get to [[GuideDangIt find]] and ultimately fight the locked-away [[spoiler:[[MonsterClown Jevil]]]], whose fight makes the FinalBoss look tame through sheer BulletHell and the difficulty of many of his attacks. Depending on how you defeat him, he'll either [[spoiler:give you the best armor]] or [[spoiler:the best weapon in the game.]]
* Gabriel Celesta and the Iseria/Isis/Ethereal Queen in ''VideoGame/ValkyrieProfile'', the ''VideoGame/StarOcean'' series, ''VideoGame/RadiataStories'', and ''VideoGame/InfiniteUndiscovery''. Also, Freya from ''Valkyrie Profile'' is the strongest boss in ''VideoGame/StarOceanTillTheEndOfTime'' where she makes a cameo appearance along with Lenneth.
* Ragu o Ragula in all of the ''VideoGame/WildArms'' games for UsefulNotes/PlayStation, [[UsefulNotes/PlayStation2 PS2]], and [[UsefulNotes/PlayStationPortable PSP]]. Angolmois also appears in some of them. In fact, the Wild [=ARMs=] games have many bonus bosses, often found [[SealedEvilinaCan sealed in crystals]] found throughout the game. Ragu o Ragula is neatly incorporated into all of these titles as the sleeping demon who is fated to destroy Filgaia, centuries after the conflict-of-the-day is finished off. Big extra credit for overachieving heroes. The other bonus bosses can range from CallBack characters, characters who are no longer a part of the main plot and have been more-or-less forgotten by the main cast, and [[ItMakesJustAsMuchSenseInContext nudie mags]]
* ''VideoGame/AWitchsTale'' has a bonus fight with friendly vampire Loue, who suddenly turns not-so-friendly for the fight. If you win, you get a game-breaking doll.
* ''VideoGame/TheWorldEndsWithYou'':
** Panthera Cantus is the toughest boss in the entire game. It has the highest attack power of all the Noise and two separate bodies; [[spoiler:a tiger on top and a lion on the bottom]]. The fight itself can be quite hectic and requires the player to pay absolute attention to what is going on in both screens.
** In addition, there are four "Boss Noise" on various days (Progfox, Grindcore Minks, Wooly AOR, and Goth Metal Drake), blue Noise symbols that lead to fights against ''much'' stronger Noise than average. For HundredPercentCompletion, you have to beat them all on Hard. Feel free to whimper.
** Additional Boss Noise symbols for every non-Bonus Boss except for the FinalBoss appear on various days after beating the game. This is more of a convenience for those going for HundredPercentCompletion, since you don't have to go through the entire chapter to fight the boss again, and can retry the fight if you didn't get what you were looking for, with the exception of the FinalBoss, which is annoying since that day has three bosses beforehand. [[spoiler:And, yes, as you may have feared by reading below, Reaper Beat and Taboo Minimimoto show up as Blue Noise as well. And, yes, you have to beat them on at least Hard in order to get all of the Secret Reports. [[RuleOfThree And, yes,]] you still need to beat Minamimoto, the harder one, on Ultimate to complete the Infinity + One Pin Deck.]]
** Unfortunately, some of these bosses were timed fights, so on your first time through, [[HoldTheLine you won if you managed to survive for 30 seconds]]. No such escape clause in the post-game, and many of these bosses are still intimidating, even having killed the final boss.
* ''VideoGame/TheWorldIsYourWeapon'': Defeating the Demon Lord is not necessary to get the first ending, but beating him is necessary for the third and fourth endings. He and the FinalBoss can also be fought in rematches so that the player can capture them. In version 2.40+, Weaco will have to fight [[spoiler:a third version of the Demon Lord to get the secret ending]].
* All three episodes of ''VideoGame/{{Xenosaga}}'' have some:
** Episode 1 has four: two mechas, Din Gareth and Jin Gareth, the sharpshooter Great Joe, and Mintia, an evil version of MOMO.
** Episode 2 has a metric-buttload of optional bosses encountered in the game's many sidequests.
** Episode 3 has two mechas: Omega Universitas [[spoiler:AKA [[VideoGame/{{Xenogears}} Id Weltall]]]] and Erde Kaiser Sigma. The latter is the only mecha in the game who's fought without the use of E.S.s.
* ''VideoGame/XenobladeChronicles1'':
** Five bonus bosses that are above the player's maximum possible level of 99 start to wander around the world after a certain point in the story: Final Marcus at 100, Ancient Daedala at 105, Despotic Arsene at 108, Blizzard Belgazas at 114, and Avalanche Abaasy at 120. Defeating them requires careful management of stat-boosting gems and the team's tactics in general.
** One long sidequest chain [[SidequestSidestory with its own story]] that covers almost half of the game leads to a bonus boss. Though this one is not overleved, it stands out because the quests that lead to it can be [[PermanentlyMissableContent lost forever]], the battle is under a tune only reserved for a few select {{Hopeless Boss Fight}}s, and [[spoiler:the boss is one of the [=NPC=]s involved in the sidequest chain: Bana, the Nopon Kingpin.]]
* ''VideoGame/XenobladeChroniclesX'', much like its predecessor, has numerous tyrants that breach the level cap of 60.
** The most powerful Tyrant is the level 99 monster Telethia, the Endbringer. It's first shown in a cutscene near the end of Chapter 6, and is later challenged in a ZeroEffortBoss fight in an Affinity mission ("The Nopon Heir"). The real battle comes during the normal mission "A Fateful Choice".
** There's also [[DualBoss Neilnail Albus and Neilnail Furvus]], a pair of [[MiniMecha Skells]] fought in the 'Twin Dolls of Mystery' Time Attack mission. [[WhatCouldHaveBeen They were originally supposed to be a story boss, but that plot thread was scrapped.]]
** The Global Nemeses, Telethia Plume and Yggralith Zero, put an interesting spin on this. They appear on the online mission list when a certain amount of multiplayer tasks have been completed, but instead of beating them, you're supposed to just deal as much damage as possible to them within 8 minutes (or until you die three times). This takes away from an absolutely '''massive''' healthpool shared across every player meaning thousands of players need to work together over the course of about a real time week to actually kill either of them.
** Completing the game adds five powerful Tyrants to the world: Dadaan, the Strongest Prone, who summons [[ZergRush his squad]] and will scrap your Skell with his bazooka if you try to use one against him; Lugalbanda, the Wanderer-King, which can debilitate you with EyeBeams and summon ovis to eat for healing; Gradivus, the Headless Emperor, a BarrierChangeBoss millesaur with a permanently destroyed neck and ''[[MarathonBoss 100 million HP]]''; Leva'el, the Terminus, a [[TheBattlestar Xern]] that summons squads of enemy Skells and Satellis units and has a OneHitKill KillSat attack; and Nardacyon, the Shadowless, a souped-up version of the Chapter 7 boss and a LightningBruiser extraordinaire that is summoned if you try to fight its pilot Nahum, the Red Hare while you're in a Skell. Some of these Tyrants drop unique weapons or special augments that add reflect effects to certain auras and Overdrives, and most of them drop unique holofigures.
** Also found in the postgame are several non-Tyrant mission bosses at or over level 60, such as Blood Despair, the Gleaming Sphinxes, Ozuchi Caladar, and Nopopon Incarnate.
* ''VideoGame/XenobladeChronicles2'' keeps up the tradition with eight bonus bosses over level 99, all but two of which appear only during the final chapter: Gladiator Orion at 100, Reeking Douglas at 104, Pernicious Benf at 109, Cloud Sea King Ken at 110, Mk. VII Arek at 114, Artifice Ophion at 117, [[KillerRabbit Chickenheart Dagmara]] at 120, and Tyrannotitan Kurodil at level 130.
* The ''Videogame/YokaiWatch'' series has this trope almost religiously in both the main and spin-off games, and a few of these bosses are noticeably harder than even the BigBad of said games.
** The first game features the Infinite Inferno, which contains palette swaps of several main story bosses, including [[spoiler:Mc Kraken's second form]] -but oddly, excluding Tarantutor- which lore-wise were imprisoned there for various reasons. The main attraction, however, is [[spoiler:Wobblewok, which causes a lot of Yo-kai energy to leak to the human world due to the seal containing him being set loose.]] Also, Chirpster and Duwheel are this for examples outside of the Inferno.
** ''Yo-kai Watch 2'' brings back the Infinite Inferno with the same bosses, but also adds the Divine Paradise, which has palette swaps of several bosses of the main story of said game -- excluding Gutsy Bones and Eyeclone, whose recolors are featured elsewhere, and Meganyan, with no recolors at all -- and has [[spoiler:Kat Kraydel as an unique boss, as she is the cause the summer is seemingly extending infinitely, as Hovernyan states at the beginning of the post-game.]] The second bonus dungeon is the Mystery Way, which features palette swaps of Gutsy Bones, Eyeclone, and Hans Full, though the three versions of the game must be connected in order to fight all four of them. In addition to bringing back Chirpster and Duwheel as well, the aforementioned Hans Full, Retinado (as part of the Gates of Whimsy sidequest) and Mallice (at the end of the Infinite Tunnel) appear as additional bosses. The 2.0 update and the third version adds Rubeus J, Hardy Hound and [[CreatorCameo Hinozall]] in the Psychic Blasters mode, and Bronzlow, Teastroyer, Infinipea, Headsteam, and Kabuking in additional sidequests and locations.
** ''Yo-kai Watch 3'' drops both the Infinite Inferno and the Divine Paradise, as well as the Mystery Way, but adds the Daruma tower, where the bosses, which are fought in the four penultimate floors are Daruma-themed palette swaps of Orcanos, Chipster, Duwheel and Slakerjack, and in the last floor, Zenlightener appears as an unique boss. These five battles are tough for you're not allowed to use items (though the Yo-kai Blaster is still allowed). Also, there are Mass Mutterer, Hinozall (both for the first time outside of Blasters), Hollow Guard in Zombie Night, Skulk in the Infinite Rice Fields, and Tornyedo (which is a palette swap and the father of ''another'' palette swap, Retinado) in a sidequest. The subsequent updates bring the Blasters Treasure mode and several old Bosses, as well as adding some new ones as a result, with [[spoiler:The Goldfather, a new form of the BigBad of the main storyline being the closest example to overlap with the BigBad of said mode]], as well as renditioning the third movie with [[spoiler:Narwail and his second form Whaleman]].
** ''Yo-kai Watch Blasters'' has, successively, [[spoiler:a haywire Robonyan 28 in the first half of the postgame]], and Kabuking, Kat Kraydel, Hinozall, and [[spoiler:Red Paws and Swirlious Omai (these two only being fought by sticking 100 friend insignia a day in the YBA hall in the opposite statue in one version and playing with a friend with the other version)]]. The Moon Rabbit Crew update adds several other bosses, some of them being examples which are oddly close to being story Bosses: Captain Thunder, Robonyan 3000, [[spoiler: Zazel/Zazelmare and his two retainers, also rendtioning the climax of the second movie]], and Golden Claws, Swirlious Gold, Hinozall Awoken, [[spoiler:Shogun King, which awoke due to the accumulated grudges from the Bosses which the Blasters defeated]], and Pink Emperor.
** ''Yo-kai Watch Blasters 2'' has [[spoiler:Sasurai Billy, which was the pirate captain mentioned in the backstory narrations in some chapters, and Majin Banbarayar, which also doubles as the endgame Boss for the Blasters' original objetive, as he grants a huge gold piece whose size depends of how the battle went, and is needed for the heroes to pay the huge debt Jibanyan had them contract and avoid the Blasters house being evicted.]] Yoderusen and Zircondor are other examples.
* ''VideoGame/YsVITheArkOfNapishtim'' has Majunun, a blowfish-like creature that guards the Eldian Orb and will kill you in one hit the first time you can access it. Just finding it is a GuideDangIt, and to have a chance of winning at all, you need to nearly max out your EXP, which takes many hours, as all the enemies only give 1 EXP on the highest few levels.
[[/folder]]

* ''VideoGame/DarkSouls'' is absolutely swarming with these guys; due to the open-ended nature of the series, it's very possible to skip a large cut of the bosses in the game just to only finish the mandatory bosses to "win" the game. [[HarderThanHard And you should be very thankful for that, a lot of the time]]. To wit:

** The game has several in the optional areas of the game. The first one most players see is the Stray Demon, a much stronger version of the tutorial's Asylum Demon that drops a highly valuable Titanite Slab. Others include the magical Moonlight Butterfly in Darkroot Garden, the illusionist Dark Sun Gwyndolin in his father's tomb, and the half-Dragon Priscilla in [[BonusLevel the Painted World.]] Priscilla is a little bit more optional tham usual because she won't attack until the player does first, and her dislogue points out that you can exit the boss arena and pass through the Painted World without a fight. The difficulty of these encounters depends on the player's progress through the game and they are much easier than the final boss, but they still provide a unique challenge to those who look for them.

* ''VideoGame/EpicBattleFantasy''

* The Doppelganger in the ''[[VideoGame/DotHackGUGames .hack//G.U.]]'' games is optional, but is ridiculously difficult and gives some of the most powerful weapons in the games.

* ''VideoGame/{{Mother 3}}'' features several. First there is Lord Passion, who carries Duster's [[InfinityPlusOneSword Infinity Plus One Shoes]], Lil Miss Marshmallow guards a decent weapon for that point of the game, and the King Statue is just there for experience and is ridiculously easy if you know what to do.

* ''[[Videogame/NocturneRPGMaker Nocturne: Rebirth]]'' has a bonus WolfpackBoss consisting of three characters from another UsefulNotes/RPGMaker game, ''Cross of the World''. After beating them once, they'll be strengthened to match a maxed-level party.

* ''VideoGame/TalesSeries''

*** [[spoiler: Abyssion]] could give some {{Creator/Atlus}} bosses a run for their money. Because of the [[spoiler: [[ArtifactOfDoom Devil's Arms,]]]] he can [[PowerCopying mimic every character's fighting style in rapid succession]], can cast the most dangerous spells in the game with barely any delay, hits like a freight train with both magic and physical attacks, and has '''[[DamageSpongeBoss 180,000 HP,]]''' ''three times'' as much as the FinalBoss. And he only [[TurnsRed gets]] [[UpToEleven harder]] when you reduce him to half HP. Martel help you if he goes into [[SuperMode Over Limit...]] [[SarcasmMode Even better,]] he is capable of using Genis's Indignation Judgement, and, in the [=PS2=] version, he can also use Lloyd and Kratos/Zelos's final attacks as well. And finally, in the [=PS2=] version? [[TheComputerIsACheatingBastard He's immune to All-Divides.]]

** ''VideoGame/TalesOfTheAbyss'' contains [[spoiler:Nebilim]], who's tests how well you are at free running and using altered artes, Reid, Mint, Nanaly, and Philia in the colliseum, the recurring Sword Dancer, as well as [[spoiler:Arietta, Largo, Sync, Arietta in a team]] and [[spoiler:Replicantis]]in the second playthrough exclusive Abyss Replica Lab.

* The ''Videogame/TraumaCenter'' series has the X operations, which have you performing [[EpilepticTrees simulated/imagined/secret/God-knows-what]] operations involving NintendoHard variations of GUILT, Stigma, or Neo-GUILT.

* In {{Creator/Konami}}'s ''NFL Football'' for the UsefulNotes/SuperNES, you can enter a code to play against the Konami team, who have A+ in all stats.

* ''Videogame/GodOfWarPS4'' has the Valkyries, who are among the toughest enemies of the games with each having a unique attack. After you defeat them all, you can challenge their queen Sigrun, who is not only stronger but has all of their attacks.

* ''VideoGame/{{Bayonetta 2}}'':

* The doujin game ''VideoGame/{{Grief Syndrome}}'' has Oktavia von Seckendorff, an optional sixth witch who can be fought [[spoiler:at any point as long as Sayaka is dead]]. This already-difficult fight is made harder by the fact that [[spoiler:you can't use Sayaka, who is generally considered the best character, against her -- as anyone who's seen ''Anime/PuellaMagiMadokaMagica'' to the end knows, Oktavia is the result of Sayaka becoming a witch]].

* ''Videogame/{{Yakuza}}'':

** There's also the Mr. Shakedowns in ''VideoGame/{{Yakuza 0}}'', a quartet of massive [[BossInMooksClothing Bosses In Mook's Clothing]] who wander the map and can massacre Kiryu and Majima in a couple hits and then take all their money. Unlike the Amon Clan, who can't be fought until near the end of the game, the Mr. Shakedowns start appearing near the start, and without lots of skill, plenty of leveling or just knowledge of their weaknesses it's suicide to take them on.

* ''VideoGame/{{Borderlands 2}}'' keeps it up with a ''number'' of such enemies, with each DLC featuring a new Raid Boss:

** The Weapon's Refrain is just as difficult. Just like the Unending Coil, this fight is a gauntlet against several bosses in a row; Specifically: Garuda, Ifrit, Titan, Lahabrea, and the Ultima Weapon. In addition to the moves they usually do being supercharged, the whole encounter is a [[PuzzleBoss giant puzzle]], as the party needs to ''[[ViolationOfCommonSense hit the Primals with their own attacks to power them up]]'' in order to obtain extra [[LimitBreak Limit Breaks]] for use against Lahabrea, and failing to do so will ''always'' result in a wipe. A Level 3 Caster Limit Break is required to destroy several [[ActionBomb self-destructing Magitek Bits]] before they explode, a Level 3 Healer Limit Break is needed to cleanse an otherwise uncleansable Doom debuff Lahabrea places on the party, a Level 3 Melee Limit Break is needed to finish off Lahabrea before he casts Dark IV to wipe the party, and a Level 3 Tank Limit Break is needed to survive the Ultima Weapon's opening attack of Ultima. Then, once the Ultima Weapon fight begins proper, ''dying to it causes it to build up its own Limit Break faster''. If the Ultima Weapon reaches 100% charge, it begins dragging players one at a time into the air and blasting them with an attack that deals 999,999 damage ''and prevents their corpses from being targeted, in turn preventing them from being raised''.

* There are several in ''Videogame/StarWarsTheOldRepublic'':

* ''VideoGame/DefenseOfTheAncientsAllStars'' and its sequel ''VideoGame/{{Dota 2}}'' has Roshan, extremely hard to defeat single-handedly, but defeating it will yield a good boon to the team that defeated it.

* VideoGame/{{Bemani}} games in general usually have an unlockable Extra Stage with one or more "boss" songs, which are always among the hardest in the game. Do well enough on that and you'll get to play the TrueFinalBoss, usually named either "One More Extra Stage" or "Encore Extra Stage", and is generally the hardest song in the game (and [[SequelEscalation gets progressively harder with each subsequent installment]]). ''VideoGame/BeatmaniaIIDX'' is known for having elaborate Extra Stage systems where, on your Extra Stage, you enter a special screen where you select one of several different boss songs. Completing all of these songs and fulfilling certain requirements on them (often a grade and special gauge requirement) will allow you to unlock and immediately play the system's FinalBoss. ''beatmania IIDX 20 tricoro'' introduces the "LIMIT BURST" system, which uses crossovers from other Bemani games as bosses.

* ''Videogame/DungeonsOfDredmor'': The real FinalBoss is Lord Dredmor himself, but a mistyped code in the third expansion brings you the chance of meeting Vlad Digula, prince of Diggle Hell. He's similar in magic prowess to Dredmor, has a bigger lifebar, but what truly makes him nastier is that trying to melee him without massive evasion rates is the quickest possible suicide you can find in a game with plenty of them.

** In the expansion pack ''VideoGame/BaldursGateIIThroneOfBhaal'', the Bonus Boss was Demogorgon, an incredibly powerful demon imprisoned at [[Main/BonusDungeon the bottom of Watcher's Keep]].

** The Cleric Beast is a boss that doesn't have to be fought in order to win the game, yet he's very commonly the first boss many players fight by virtue of gating off exploring more of Yharnam, and he [[EstablishingSeriesMoment establishes the de facto nature of the game]] by being ''very'' aggressive unlike almost any other boss in ''Dark Souls'', and actively punishing tactics of turtling by forcing you to be constantly on the offensive while dodging each of the Cleric Beast's attacks. For many players, it serves as a WarmUpBoss and in many ways equivalent to ''VideoGame/DarkSouls3'''s own Iudex Gundyr for being the "tutorial" boss.

* ''Videogame/DarkSoulsII'' has several:

* ''VideoGame/{{Borderlands}}'' has some in the optional side quests, some of which, like Mothrakk and Marley & Moe, can reach ThatOneBoss status. The ''true'' Bonus Boss doesn't come until you've downloaded and finished ''The Secret Armory of General Knoxx''. That unlocks a fight against Crawmerax the Invincible. In case it's not clear, the game spells it out for you: the quest where you have to fight him is called '''"You. Will. Die."''' And the road leading to Crawmerax's lair features a road sign saying "[[LampshadeHanging Secret Final Boss]]".

** The ''Legion'' expansion added what had to be the most GuideDangIt case of this yet, in the form of Endgineer Omegaplugg. To fight him, you have to take a max-level group into the low-level dungeon of Gnomeregan, work your way to the normal final boss of that place, and then find and press a hidden button in that room to summon him. Omegaplugg has many AOE abilities that can two-shot endgame-geared characters, making the fight extremely difficult on top of all that.

** [[PoisonousPerson Volk]] is the first of the Agito who has an utter hatred of anyone of privilege whether they use it for good or evil and will see them dead. His mechanics involve hitting the party with Plague which reduces resistances while he sends out flying disks around the arena. Underdog's Scheme sends out four gas clouds, two each having stun and sleep clouds that supercharges anyone who runs into it, otherwise it causes massive AoE damage, if not leading to a wipe.

** There's another boss Deathclaw in ''Lonesome Road'', named Rawr. It's a LightningBruiser, even compared to the Alpha Male, and will kill most characters in one hit; it has somehwhat less HP than the Legendary Deathclaw. Defeating him allows you to build one of the most powerful Unarmed weapons from his talons, Fist of Rawr. [[spoiler: Or [[Manga/FistOfTheNorthStar Fist of the North Rawr]] if you have [[SillinessSwitch Wild Wasteland!]]]] There's also Gaius Magnus and Colonel Royez, who are only available [[spoiler:if you choose to nuke the Legion or NCR respectively at the end.]] Both have all of their SPECIAL stats maxed out, and Royez has the third highest HP of any human enemy after Ulysses and Legate Lanius, a Damage Threshold of 24, wields a plasma caster with overcharge ammo, and regenerates his HP very quickly from the radiation.

* They exist in many ''VideoGame/FinalFantasy'' games:

** The PSP VideoGame/FinalFantasyI remake ups the ante with Chronodia, who has 8 FORMS! It's not a SequentialBoss, though; which one you fight depends on how you did in the BonusDungeon prior to fighting her. Either way, she's pretty hard.

* ''VideoGame/MarioAndLuigiBowsersInsideStory'' has several: [[spoiler:the frozen Shroob trio in Bowser's Castle, the X bosses, and Bowser X.]]
* ''VideoGame/MarioAndLuigiDreamTeam'' also has [[spoiler:the X bosses, with giant bosses now having X forms. Taking Bowser X's place is Bowser Jr.]]
* ''VideoGame/MarioAndLuigiPaperJam'', once again, brings back [[spoiler:the X bosses, but having dropped the X - same concept, but with no name. Bowser X and Bowser Jr. are succeeded by Dry Bowser]].

** Bloopers who shows up every time you find a new shortcut in the sewer (though the last one is mandatory). Kent C. Koopa also blocks a road and makes you pay to pass; beating him lets you pass for free. Then there is a Dojo, where you can fight for bragging rights. The final blooper, Kent C., and the Dojo Master could all give Bowser a run for his money if he didn't have the Star Rod.
** There's also the [[BossInMooksClothing Anti Guy]], found guarding a chest in a dungeon halfway through the game and with HP and attack roughly on par with Bowser's penultimate form. He can be beaten straight-up, or you can exploit his SweetTooth to bribe your way to the chest's contents.
** In Chapter 8, if you flunk a quiz from one of the Bowser-faced stone doors, your punishment will be a NoHoldsBarredBeatdown against ''three'' Anti Guys. Easily the most difficult fight in the game, as Mario will initially be taking in the ballpark of 25-30 damage a turn with (unlike all the above bosses) no way to cheese your way out of it.
* ''VideoGame/PaperMarioTheThousandYearDoor'':
** Bonetail gives the game's final boss a run for its money (which is lampshaded by [[MetaGuy Goombella]]) and requires going through a dungeon with 90 consecutive battles (99 floors with a "breather" every 10) to reach him. He is a bit easier than the final boss, as you'll probably be better equipped and levelled by the time you reach him, and his attacks aren't as complex to deal with -- he just has enormous attack power and endurance, and getting to him is a massive two hour-long ordeal.
** Atomic Boo, fought in Creepy Steeple if you enter the main hall and take the Spin Hammer attack to the swarms of Boos enough times. He isn't particularly hard, but knowing he even exists is a bit of a GuideDangIt.

** ''VideoGame/PokemonRedAndBlue'': You can find Articuno in the Seafoam Islands, Zapdos in the Power Plant, and Moltres on Victory Road. Mewtwo can be found in Cerulean Cave after you become the Champion. The use of cheats also enables the player to battle ''Professor Oak'' in the original ''Red/Blue'' versions, with a team of higher levels than the Champion. Some fans speculate that he was supposed to be a TrueFinalBoss and got removed from the storyline, [[DummiedOut but the producers forgot to remove his battle data]], since Agatha of the [[BossRush Elite Four]] states that he is a RetiredBadass. Sadly, he didn't get any battle data in ''[[VideoGameRemake FireRed/LeafGreen]]''. They did add one more in ''[=FireRed=]'' and ''[=LeafGreen=]'', though: once you've obtained the National Dex, one of Johto's legendary beasts will begin roaming for you to capture - whichever one has a type advantage against your starter (Entei for Bulbasaur, Suicune for Charmander, and Raikou for Squirtle).

*** ''[[VideoGameRemake HeartGold]]'' [[TheRemake and]] ''[[VideoGameRemake SoulSilver]]'' have a boss Trainer that can only be fought by having a Celebi: [[spoiler:Giovanni]]. This Trainer isn't very difficult, however, and mainly serves to tie up some loose story ends. They also add more Legendaries; once you've earned the National Dex, you'll be able to find Latios (SS) or Latias (HG) after visiting the Fan Club in Vermilion City[[labelnote:*]]If you have the event-only Enigma Stone, you can fight the other Eon Pokémon in Pewter City[[/labelnote]]; once you've beaten all sixteen Gyms, you can challenge the four Kanto Legendaries; and once you've beaten Red, you'll have completed the hardest prerequisite to battle Groudon for SS and Kyogre for HG, and Rayquaza if you have both in the same game.
*** The [[GameMod ROM hacks]] [=SacredGold=] and [=StormSilver=] come with a number of bonus bosses. First, after completing the game, the player may face the player character they didn't pick. RecurringBoss Eusine allows the player to have a rematch with him. [[VideoGame/PokemonRubyAndSapphire Steven]] appears to ask the player for a battle, as does [[VideoGame/PokemonDiamondAndPearl Cynthia]]. After capturing Mewtwo, the player may return to his location, and face off with [[TheRival Silver]], who uses a team of three OlympusMons, in reference to [[VideoGame/PokemonStadium Pokemon Stadium 2]]. Lastly, should the player [[GottaCatchEmAll Catch Em All]], then they may head to the Sinjoh Ruins, and battle with [[PhysicalGod Arceus]].

*** ''VideoGame/Persona2'' was the sub-series's first entry in this list with Philemon's brutal bonus battle on his EX Dungeon. Notably, he's the ONLY enemy, let alone boss, in the entire game who is immune to the Fusion Skill Armageddon, which, if used, can one-shot even the final boss. Try to use it on him, and he'll hit back with Armageddon R, wiping your party without fail and leading to a game over.

*** ''[[UpdatedRerelease Persona 5: The Royal]]'' adds a new boss fight in the Third Trimester against [[spoiler: the Twins' combined true form, Lavenza]]. Unlike the Twins, this is just a single boss, but in exchange, they utilize advanced tactics such as using buffs and debuffs and have resistances that constantly shift throughout the fight. [[spoiler: And they can still perform an All-Out Attack by splitting back into the Twins if given the chance.]]

* ''VideoGame/SuperPaperMario'': [[spoiler:The first of the three bonus bosses is really another version of the game's first boss. To even face the second boss, you have to clear a dungeon filled with even stronger enemies that are all pitch black, making distinguishing subtypes near impossible without Tippi/Tiptron until it's too late. '''''Twice.''''' The third is the 100th Sammer Guy, End Boss, the only one of them who cannot be fought until the postgame.]]

* ''VideoGame/XenobladeChronicles'':

* ''VideoGame/{{Ys}} VI: The Ark of Napishtim'' has Majunun, a blowfish-like creature that guards the Eldian Orb and will kill you in one hit the first time you can access it. Just finding it is a GuideDangIt, and to have a chance of winning at all, you need to nearly max out your EXP, which takes many hours, as all the enemies only give 1 EXP on the highest few levels.

* In the ''VideoGame/FireEmblem'' franchise:

* ''VideoGame/{{Xenoblade}}''

* The ''Videogame/{{Yakuza}}'' series has Jo Amon and the other members of the Amon Clan appear as the ultimate boss in every game, including the spinoffs. For most of them, you can only fight them after completing every other substory in the game.

* ''Dungeon Siege'' has two. One is easy to find, while the second is extremely hard. The first is Scorch, the ancient dragon of Rathe, whom the player could avoid simply by continuing by the road to Castle Ehb. Scorch is the biggest monster in the game, has the highest number of HP, and is nearly as deadly as the final boss. The second Bonus Boss is located in the hard-to-find secret "Chicken level", amongst the various chickens named after the game's developers. It is [[spoiler:Colonel Norick, the boss version of the first NPC quest giver in the main game, an old man who dies in front of the player. He also is a spoof on Colonel Sanders of KFC fame]].

* Used in a rather creative way in ''VideoGame/SevenSamura20XX'': The third chapter features a whole, confusing city to explore, and before the series of events leading to the last boss fight that will end the level, you can encounter a series of unique NPC which can be challenged and fought as bosses in various parts of the city, namely Pyro (a guitarrist with a garish green outfit and pink afro), Morozumi (a sexy black woman covered in bandages and using kunai), Tsubaki Dayu (a graceful masked woman warrior), Gotehnmaru (a warrior in a nice suit), Oniwaka (a massive man in a kendo suit), Ushiwaka (A ninja-like swordsman) and finally Brahman (a magician-like fighter who can turn invisible). Defeating them has no impact on the plot, but once you finish the game they unlock the Arena Mode where you can fight against all previous bosses.

* ''VideoGame/SkiesOfArcadia''::
** The original game has some. You don't have to fight any of the giant monsters (Obispo, the Roc, the Giant Looper, and Alania). There's also [[MetalSlime Elcian]], a super Looper who appears in the Dark Rift near the end of the game, who puts up a tough fight but gives good experience and loot and can be fought multiple times, making him great for LevelGrinding. And finally, OneHundredPercentCompletion unlocks one final battle against [[spoiler:Air Pirate Vigoro]].
** The bounty bosses in ''Legends''. They are also ThatOneBoss -- because even for a bonus boss, their difficulty is sadistic.

* Gabriel Celesta and the Iseria/Isis/Ethereal Queen in ''VideoGame/ValkyrieProfile'', the ''VideoGame/StarOcean'' series, ''VideoGame/RadiataStories'', and ''VideoGame/InfiniteUndiscovery''. Also, Freya from ''Valkyrie Profile'' is the strongest boss in ''VideoGame/StarOceanTillTheEndOfTime'' where she makes a cameo appearance along with Lenneth.
* Ragu o Ragula in all of the ''VideoGame/WildArms'' games for UsefulNotes/PlayStation, [[UsefulNotes/PlayStation2 PS2]], and [[UsefulNotes/PlayStationPortable PSP]]. Angolmois also appears in some of them. In fact, the Wild [=ARMs=] games have many bonus bosses, often found [[SealedEvilinaCan sealed in crystals]] found throughout the game. Ragu o Ragula is neatly incorporated into all of these titles as the sleeping demon who is fated to destroy Filgaia, centuries after the conflict-of-the-day is finished off. Big extra credit for overachieving heroes. The other bonus bosses can range from CallBack characters, characters who are no longer a part of the main plot and have been more-or-less forgotten by the main cast, and [[ItMakesJustAsMuchSenseInContext nudie mags]]

* ''VideoGame/GoldenSun'':
** ''VideoGame/GoldenSun1'' has Deadbeard, an undead pirate found at the bottom of Crossbone Isle, who guards the game's most powerful armor. One path to him contains another bonus boss, a weather controlling lizard. A third bonus boss has its own bonus ''Town'' outside the BonusDungeon, and is a gigantic acid frog.
** ''VideoGame/GoldenSunTheLostAge'' has the Star Magician, Sentinel, Valukar, and Dullahan. The [[FlunkyBoss Star Magician]] summons mooks to use Jupiter psynergy on you, buff and heal the Magician, and explode for huge damage. Sentinel constantly buffs his defense and is immune to all psynergy, meaning he gets tougher and tougher. Valukar can knock your Djinn into Standby and use your summons against you with Crucible. And [[MemeticBadass Dullahan]] can put every active party member's Djinn into recovery with Djinn Storm, gets three moves per turn, and hits like a runaway cement mixer.
** In ''VideoGame/GoldenSunDarkDawn'', Star Magician and Dullahan get buffed up, with Star Magician getting three new mook types (Curse, Death, and Ghoul) and Dullahan getting Valukar's Crucible move. There's also the Ogre Titans, a group of five increasingly powerful physical attackers, and the Ancient Devil, who can take over one character with Demon Sign.
** In the early parts of ''Dark Dawn'', if you try to beat the Psynergy Training Grounds a second time, the Dim Dragon gets an upgrade, making it an early-game Bonus Boss.

* ''VideoGame/MarioAndLuigiBowsersInsideStory'' has several: [[spoiler:the frozen Shroob trio in Bowser's Castle, the X bosses, and Bowser X.]]
* ''VideoGame/MarioAndLuigiDreamTeam'' also has [[spoiler:the X bosses, with giant bosses now having X forms. Taking Bowser X's place is Bowser Jr.]]
* ''VideoGame/MarioAndLuigiPaperJam'', once again, brings back [[spoiler:the X bosses, but having dropped the X - same concept, but with no name. Bowser X and Bowser Jr. are succeeded by Dry Bowser]].
* The ROMHack ''Super Mario RPG Armageddon'' adds a ton of NintendoHard bonus bosses, including [[VideoGame/FinalFantasyIX Ozma]], [[VideoGame/FinalFantasyX Penence]], [[VideoGame/FinalFantasyXII Yiazmat]], [[VideoGame/FinalFantasyVI Goddess, the Elemental Dragons, Kaiser Dragon]],[[VideoGame/FinalFantasyIVTheAfterYears Mysterious Girl]], [[VideoGame/SuperMarioGalaxy Rosalina]], [[VideoGame/PaperMarioTheThousandYearDoor The Shadow Queen]], [[VideoGame/ChronoTrigger Magus and Schala]] (as a DualBoss), [[VideoGame/PaperMario Anti Guy, General Guy, The Master]], and the two most powerful bosses of all: [[spoiler: [[VideoGames/KingdomHearts358DaysOver2 Xion]]]] and [[spoiler: [[VideoGames/FinalFantasyVI Terra]]]].

*** The game had at least 6 hidden bosses [[spoiler:(Seles, Abyssion, Maxwell, three former Tales characters (Woodrow/Garr, Farah, and Meredy), and the Sword Dancer, and the Living Armor at the end of [[BrutalBonusLevel Forbidden Anamnesis]])]], the second of which gives you [[InfinityPlusOneSword weapons]] that makes the rest of the game ridiculously easy - [[BraggingRightsReward as if it weren't already for anyone powerful enough to defeat him in the first place]].

* ''VideoGame/MonsterHunter'' has several examples, mostly reserved for multiplayer (whether local, online or both):
** The four-legged Elder Dragons (not to be mistaken with the two-legged wyverns) in most games, as well as Kirin the lightning unicorn. Most of them only appear in the highest-tier quests.
** In ''Freedom'', Yian Garuga is unlocked after hunting 10 Yian Kut-Ku. Its quest is rated with six stars (the highest grade), and it's ill-advised to challenge it until you have a decent postgame gear. In ''Monster Hunter 2'', it can only be unlocked via OldSaveBonus by connecting both games through an USB.
** In ''Freedom 2'' and ''Portable 3rd'', Gold Rathian and Silver Rathalos are unlocked by killing or capturing a combined total of 100 large Wyverns (also including Leviathans in the latter game). Note that ''Freedom Unite'' averts this trope with them, since their respective quests are mandatory in order to unlock the G Rank chapters. From ''3 Ultimate'' onwards, they're available as soon as you reach the highest-tier quest chapter, thus are demoted to merely [[SkippableBoss skippable monsters]].
** In ''Portable 3rd'', Akantor and Ukanlos ([[LegacyBossBattle originally the respective final bosses of]] ''Freedom 2'' and ''Freedom Unite'') can be fought after completing all single-monster quests in the prior high rank quests, while Alatreon (of ''Tri'' fame, [[LegacyBossBattle also its online final boss]]) is unlocked upon completion of all DualBoss monster quests.
** In ''3 Ultimate'', Hallowed Jhen Mohran is only accessible after the player slays or captures every single large monster (including previous Elder Dragons like regular Jhen Mohran and Alatreon) except Savage Deviljho, Lucent Nargacuga and Abyssal Lagiacrus (which happen to be Bonus Bosses on their own; as Savage Deviljho can only be fought in quests with unstable environments or alternatively through a DLC quest, Lucent Nargacuga is unlocked after reaching HR 40, and Abyssal Lagiacrus is unlocked after reaching HR 70).
** The endgame multiplayer quests of the original version of ''Monster Hunter 4'' consists mostly of souped-up versions of monsters you've previously fought, such as Akantor or Dalamadur, though it also adds the debuting Molten Tigrex (HR 50) and series classic Fatalis (HR 70). The expansion ''4 Ultimate'' repeats the trend for G Rank via the Aged Texts, having buffed familiar monsters while also adding Shah Dalamadur and Raging Brachydios. ''4 Ultimate'' also has the quests where you fight Apex versions of monsters, each of which is unlocked through a specific condition.[[note]]For the Apex Tidal Najarala, Gravios, Diablos, Tigrex and Zinogre, you have to hunt a specified combined total of specimens of the species and related subspecies in question. For the Apex Seregios and Rajang, you have to decipher the third and sixth Aged Texts respectively. For Apex Deviljho, you have to clear any of the previous Apex monster quests and accept the Deviljho Arena challenge in the Assembly[[/note]]
** ''Generations'' has the twelve Deviants, monster specimens that have survived numerous battles with Hunters and other monsters and have developed unique and deadly traits. All of them are optional and can only be fought through a unique series of quests. Hunters must spend special permits to post these quests because of how dangerous the Deviants are. Indeed they are, as the first, [[BearsAreBadNews Redhelm Arzuros]], is a notorious WakeUpCallBoss, and the rest go up from there. The expansion ''Generations Ultimate'' adds six more, including the Bloodbath Diablos, who can only be fought after hunting the other five new Deviants at least once and defeating the final boss. ''GU'' also has the Extra Special Permit Quests at the end of each Deviant's quest chain, which feature a Deviant with health, attack, and resistance buffed UpToEleven, require HR 100 to join, and have no supplies provided. EX Deviants are not required to defeat to max out Deviant weapons nor earn achievements, but doing so rewards a shiny color palette, Guild Card titles and special icons, and unlocks the ability to fuse Deviant armor.
** ''[[VideoGame/MonsterHunterWorld World]]'' has the monsters added after the game's release through free title updates: Deviljho, Kulve Taroth, Lunastra, [[Franchise/FinalFantasy Behemoth]], [[Franchise/TheWitcher Leshen]], Rajang, Stygian Zinogre, Safi'jiiva, Raging Brachydios, Furious Rajang, Alatreon, Frostfang Barioth and Fatalis. With the exception of Deviljho, who can be encountered randomly partway into High Rank, they can only be fought after defeating the final boss and during their respective questlines. Additionally, there are Arch-Tempered Elder Dragons, souped-up event-exclusive Elder Dragons with increased strength and sometimes new attacks and behavior that require HR 50 to fight, attainable only in the postgame.





* In the ''VideoGame/MegaManBattleNetwork'' series, there is so much extra content and so many bonus bosses that the time taken to defeat them is longer than the main story line. In all of them, however, you face Bass/Forte. Unlike other continuities, here he is a god-like badass.
* ''VideoGame/MegaManStarForce'':
** Usually there's a secret area after beating the FinalBoss where you have to fight upgraded forms of each boss in the game, followed by an all-new secret boss. After doing that, the storyline's final boss is upgraded, with it being the truly strongest boss in the game. The only exception to this is the second game, where after beating the upgraded final boss, you fight [[spoiler:an upgraded Rogue after the credits finish.]]
** You can also engage a number of repeatable bonus bosses and random people who can Wave Change in ''2''. These include second shots at the storyline bosses to get their Mega cards, plus farmable bosses like Kung Foo Kyd, Gemini Spark, and Cancer Bubble.
** The third game has a rather unusual take on this with the Omega versions of the bosses, as they can rarely appear virtually anywhere in the game, and also at any point in the story, even before you've fought their regular versions. It's entirely possible to run into one of them ''right after the gameplay tutorial'', despite even weakest of them being far stronger then the final boss. Fortunately, the game is nice enough to not give you a game over for losing to them and also alerts you of their presence by changing the music in the area to a very ominous tune.
* ''VideoGame/MegaManXCommandMission,'' meanwhile, had two Bonus Bosses plus another set of nine. Rafflesian and Duckbill Mole gave X, Zero, and Axl new abilities that were useful in what remained of the game by that point. Ninetails and the preceding eight Tails Clan members, on the other hand, who were definitively even more this trope, could only be fought ''after'' beating the final boss, making the rewards for beating ''them'' [[BraggingRightsReward worthless.]]


* ''Franchise/ShinMegamiTensei'': Creator/{{Atlus}} has loved making [[ThatOneBoss these noble fellas]] to rain Megidolaons upon us since the early 90's:
** ''VideoGame/DigitalDevilSaga'':
*** The [[spoiler:Demi-Fiend]] battle in the first one, one of the hardest bosses in the history of {{JRPG}}s, if not ''the'' hardest boss. Not only will he instantly kill you in the first turn if you have a "forbidden" move set (read: any passive or castable move intended to null, absorb or repel enemy attacks), but the strategy required to defeat him requires a very specific use of one usually worthless skill that you would ''never'' use in the main game (to wit, the Null Sleep skill, which nulls all damage one would receive while asleep). How anyone could figure this out without the use of a strategy guide is a mystery for the ages. Beating him unlocks an useful accessory that you can find midgame through the sequel that boosts all stats by 10. And even then, if you do manage to get him down to half health, his High Pixie will fully heal him. If you kill all of his demon companions, he'll insta-kill you. If you go in with any protective moves, he'll insta-kill you. Hell, even with the correct strategy, if you take too long to kill him, he'll just get bored and insta-kill you anyway. To add insult to injury, his battle music is the ''regular Nocturne battle music'', so he may be an uber hard bonus fight to you, but you're nothing more than ''a random encounter'' to him.
*** [[spoiler:Satan]] in the sequel is likewise enormously difficult, if a lot less so than the [[spoiler:Demi-Fiend]]; you require to continuously cast Charge to boost all your stats to max so [[spoiler:Satan]] won't cast God's Breath, his insta-kill move. If you did so, good, he'll only cast Dekaja and put you back at square one. Hurt him enough and take too long and he will cast Diarahan, putting himself back at full health. Anyway, even without their instant kill skills, both are beastly difficult -- you ''need'' to cap out your major stats to even have a fighting chance, and ''then'' there's the actual strategy involved... which simply fails half the time due to bad luck. You also cannot fight [[spoiler:Satan]] on Normal Mode; you explicitly ''have to be'' playing on Hard Mode or your team will be too fearful to even enter his room.
*** TheFourGods: Each appears in a different sector in the first game, each representing a specific element. Avoid repelling their elemental attacks or hitting them with their respective elements and they will go down fairly easily.
*** Huang Long: Appears high in the Karma Temple after killing TheFourGods. Hits like a truck with the Almighty-type Celestial Ray, which also slaps you with any ailment he wants. Has tons of HP and can cycle through several forms to make the task of damaging him harder. Still not as hard as the [[spoiler:Demi-Fiend]].
*** Beelzebub's two forms: Baal Zabul appears in Svadhisthana's underbelly once you unlock it with the Red Key. While he ''is'' somewhat strong, he's really nothing to be worried about. Beelzebub proper appears after Baal Zabul's defeat in the Manipura Waterways, and comes back with a vengeance, packing the lethal ''Death Flies'' move, which will kill anything not protected against Dark attacks with 100% effectiveness. Even if your charaters ''are'' protected, it will hit with a horribly strong Almighty-type attack.
*** Orochi is the last obstacle in the path to the Red Ring, required for another boss. He has ''eight'' actions on his turn, can exploit elemental affinities and Criticals with Ice and Lightning attacks, abuse Makakaja and Megidolaon, and has a crapload of resistances. However, he has pathetically small MP for a boss, and will try to restore his tanks with yours. With Null Mute, he turns into a joke after a few turns.
*** Metatron fights you after you enter Ajna with the Red Ring and killed TheFourGods. He likes to abuse Makakaja, Revelation, and Fire of Sinai, which can hit several times for Almighty damage with the possibility of instant death.
*** King Frost appears at Coordinate 136 after the defeat of Mick the Slug. Finish the minigame of "find the key" and King Frost will appear at the Princess's Bedchamber. He spams Cocytus, which will almost always freeze, and summons overleveled Jack Frosts to pound you.
*** In the second game, there are fights against the Four Archangels, Shiva, Vishnu, Jack Frost and Seth. The Shiva and Vishnu fights also require you to find a special item for each, from Parvati for Shiva and Narasimha for Vishnu. The pathway to Seth is blocked off until you defeat Shiva and Vishnu and Seth himself blocks the way to [[spoiler:Satan]].
** ''VideoGame/ShinMegamiTenseiI'' and ''VideoGame/RaidouKuzunohaVsTheSoullessArmy'' has Beelzebub. ''Soulless'' is particularly vicious as he requires three items to be fought, all of which have to be acquired through ZergRush battles with 100 enemies each; these will tend to be DemonicSpiders. Then, he will be fought amidst ''another'' ZergRush. Pray none of your healing demons get Charmed, as he will use and abuse any attacks which can inflict said ailment to jack up his health.
** ''VideoGame/ShinMegamiTenseiStrangeJourney'' has the NGP-exclusive [[PowerLimiter Alilat]] and [[PhysicalGod Demiurge]]. Alilat has the game-breaking combo of high Magic stat, Mind Charge, and Megidolaon-a nigh-guaranteed TotalPartyKill. Demiurge is a BarrierChangeBoss, has Big Bang which deals even more raw damage than Megidolaon, regularly heals himself with Diarama, and has a ton of HP. Additionally, he's fast enough to dodge most of you attacks and has all of the deadliest elemental spells.
*** The UpdatedRerelease, ''Strange Journey Redux'', introduces a quartet of even stronger bosses under the command of Louisa Ferre, available only on a NewGamePlus. Belial, Lucifuge, Nebiros, and Beelzebub are all capable of shuffling their weakness and obscuring their analysis data after you've just exploited it for free Co-Op damage. They also have very high stats across the board, and if taken too long to defeat, will bombard your party with Doomsday which is almost guaranteed to kill. If you consider the Womb of Grief a BonusDungeon (as it's not mandatory for the main plot, but does unlock the new endings) then its associated bosses qualify for this trope.
** ''VideoGame/RaidouKuzunohaVsKingAbaddon'' has Masakado and Lucifer.
** ''VideoGame/ShinMegamiTenseiI'' has Beelzebub as the ultimate Bonus Boss, but there were others, such as the series's first three Fiends: Daisoujou, David, and Pale Rider.
** ''VideoGame/ShinMegamiTenseiII'' brings back Beelzebub as the ultimate boss. There are also the Fiends, of which there are five this time: Alice, Hell Biker, Ghost Q, the Sage of Time, and Matador.
** ''VideoGame/ShinMegamiTenseiIIINocturne'' plays around with this. The bosses of the UpdatedRerelease are required for the new ending, but many consider them Bonus Bosses as well. These include all of the Fiends (save Matador and the first fight with [[VideoGame/DevilMayCry Dante]]/[[VideoGame/RaidouKuzunohaVSTheSoullessArmy Raidou]] [[VideoGame/RaidouKuzunohaVsKingAbaddon Kuzunoha XIV]], who is required), Beelzebub, and Metatron. Also present but unconnected to this questline are the Buddhist Four Heavenly Kings, who reside at Bandou Shrine, have maxed stats and the most powerful attacks of their respective elements, and guard the game's most powerful [[AmplifierArtifact Magatama]].
** ''VideoGame/ShinMegamiTenseiIV'' has both the Fiends (Matador is one example) and the DLC Bosses ([[spoiler:The Four Archangels, Ancient of Days, Sanat, and Masakado.]])
*** The game also has a plethora of bosses that can only be fought in their respective challenge quests. While the majority of them pale in comparison to the monsters already listed (the main exceptions are Beelzebub ([[OnceAnEpisode of course]]) and the New Game + exclusive Astaroth), they still count since most challenge quests are optional. Other than the aforementioned opponents, there's one particularly strong Bonus Boss for each route (though they don't compare to the Fiends, DLC Bosses, Beelzebub, and Astaroth, they're still stronger than other Challenge Quest bosses): [[spoiler:Mastema for Law, Demiurge for Chaos, and Shiva for Neutral, with the first two coming form Challenge Quests and the last being the Terminal Guardian's final battle]].
*** Special mention must go to the Fiends. Seven of these Fiends (Matador from above being one of them) can only be found in certain locations and the chance of actually encountering them is very low (1 out of 256). Each one has at least five Press Turn icons, will always get the first strike, and will spam Antichthon (massive Almighty damage and all stats lowered) or similar skills if they cannot safely attack you or your demons with their preferred attacks. Defeating them will unlock them for special fusion, and often, a wonderful reward, including some of the game's best equipment.
** ''VideoGame/ShinMegamiTenseiIVApocalypse'' brings back the Fiends along with [[spoiler:En no Ozuno from the first game]]. DLC adds [[spoiler:Mephisto, Cleopatra, and a demonic Hope and Hugo]]. The final DLC makes the ultimate opponent [[spoiler:Stephen, who fights against every numbered SMT protagonist at once]].
** ''Franchise/{{Persona}}'':
*** ''VideoGame/Persona2'' was the sub-series's first entry in this list with Philemon's brutal bonus battle on his EX Dungeon. Notably, he's the ONLY enemy, let alone boss, in the entire game who is immune to the Fusion Skill Armageddon, which, if used, can one-shot even the final boss. Try to use it on him, and he'll hit back with Armageddon R, wiping your party without fail and leading to a game over.
*** ''VideoGame/Persona3'' has Velvet Room attendant Elizabeth. She can only be fought on the second playthrough by accepting her 55th request and going to the top of Monad. She seems to be nothing more than a thin blonde girl dressed like a bellhop, but she is the most powerful foe in the game, can only be fought one-on-one (she'll kill any other party members right away), gets to attack twice every turn (where you can only attack once), has multiple personas and powerful attacks, and heals herself completely when at low health. Even worse, if any of her attacks are nullified, reflected, or absorbed (which they invariably will be, considering her attack rate and huge range of attacks), she goes berserk and spams a 9999-damage attack (out of max possible HP of 999) nonstop until you die. Amusingly enough, the UpdatedRerelease version of the game features an upgraded version of your starter Persona which seems to be tailor-made to fight her, as it resists every type of attack, giving you a good overall defense against anything she tosses out and avoiding driving her berserk.
*** While nowhere near as insane as Elizabeth, the Reaper that can be fought in both version of P3 is no slouch when it comes to making a normal player tear their hair out. It's fond of casting spells that hit the whole party for 700-800 damage and going insane on unblockable "almighty" spells if the player sets up reflecting items. This one is more infuriating to the average player due to the fact that he appears when the player spends too long in Tartarus, the game's central randomly generated dungeon. It makes a return in ''VideoGame/Persona4'', and is found while opening a chest (the game warns you about it and gives you two chances to back out). It returns again in ''VideoGame/Persona5'', where it'll appear if you stay too long on one level of Mementos, though this time around it's possible for it to [[WorfHadTheFlu catch the flu]] during certain days, severely weakening it.
*** ''Persona 3 Portable'' allows you to fight Velvet Room attendant (and Elizabeth's brother) Theodore if you make the proper choice early on in the game (it's not dependent on gender). However, it cranks things up to 11 with the Vision Quest, which not only contains more difficult versions of the Arcana Shadows, but also allows you to fight [[spoiler:Margaret! Yes, the one in the next example. You can still use your full party, but that doesn't make things any easier...]]
*** ''VideoGame/Persona4'' continues the tradition with Velvet Room attendant (and Elizabeth and Theodore's big sister) Margaret, who is unlocked by reaching the True Ending after clearing Margaret's Social Link and killing the six other optional bosses (see below). While you can bring in party members and she won't (immediately) wipe them, she's just as frustrating. Nice changes include only healing once. She'll still 9999 Megidolaon you if you bring in a forbidden item, and do so on you every 50 turns. She'll also exploit 1 More relentlessly if you give her the chance in the pattern. She won't kill you if you reflect or nullify her spells, but she shifts her weaknesses around so that she heals if you reflect a spell at her. ''Golden'' increases her difficulty by allowing her to go twice every turn, essentially halving the time it takes for her to use Megidolaon, as a way of offsetting the various new features that make things easier.
*** After defeating a dungeon's main boss in ''4'', a new, optional boss appears in the original's place. These tend to be [[EarlyBirdBoss a few orders of magnitude harder]]. If you fight the Contrarian King as soon as he becomes available, you will die. If you fight him after making your way through the next dungeon and bumping up a good 10 or 15 levels... you'll probably still die. His Rampage attack is overpowered enough to wipe your party in one shot, and he gives himself Fire resistance as soon as the battle starts. [[spoiler: Fire ''heals'' him. He has no actual weaknesses.]] Naturally he's the first Bonus Boss to become available, and the game will [[SchmuckBait encourage you to challenge him well before you're ready]]. The others aren't quite as difficult, and some actually have elemental weaknesses. If you defeat them, you're rewarded with a large Courage boost and a useful piece of equipment hidden in the boss room.
*** ''VideoGame/PersonaQShadowOfTheLabyrinth'' continues the tradition of having the residents of the Velvet Room be overpowered bonus bosses, though for the most part things are a bit easier. You can fight Elizabeth several times throughout the game, with her difficulty slowly increasing over time [[spoiler:and eventually, she's possessed by Zeus]]. Margaret is also an optional battle, in which [[spoiler:you fight her two on one with the protagonist you didn't pick, in order to unlock your ultimate Personas]]. However, it wouldn't be a crossover game if you didn't have a chance to fight Elizabeth, Theodore, and Margaret simultaneously. They can even do an [[CombinationAttack All-Out Attack]] every five turns, though they're more forgiving than they are in the base games.
*** ''VideoGame/Persona5'' once again continues the tradition of overpowered Velvet Room attendants with Caroline and Justine. Like the ''Persona Q'' battle against Elizabeth, Theodore, and Margret, they battle you as a team. Thus when one falls, the other will revive them, and they can do an [[CombinationAttack All-Out Attack]] when all your team is knocked down. They can also use the new Baton Pass command, making it even more imperative to make sure they don't hit any of your weaknesses.
*** ''[[UpdatedRerelease Persona 5: The Royal]]'' adds a new boss fight in the Third Trimester against [[spoiler: the Twins' combined true form, Lavenza]]. Unlike the Twins, this is just a single boss, but in exchange, they utilize advanced tactics such as using buffs and debuffs and have resistances that constantly shift throughout the fight. [[spoiler: And they can still perform an All-Out Attack by splitting back into the Twins if given the chance.]]
*** ''VideoGame/PersonaQ2NewCinemaLabyrinth'', like the first game, features a fight with all the Velvet Room attendants. This time, there's four phases- Caroline and Justine fight you in the first phase, alongside Margaret in the second phase, Theodore in the third phase and Elizabeth in the fourth phase. In the lead-up to this huge fight, you get to fight each attendant (the twins are fought together) separately, one fight for each Sooty Film you collect from a Special Screening set at the final floor of each movie.
** ''VideoGame/DevilSurvivor'' holds a few bonus bosses. They appear as unique Free Battles that don't advance the clock. The ''Overclocked'' UpdatedRerelease adds a few more.
*** Ghost Q shows up on Day 2, offering treasure. If you select the correct card (it's totally random), you can complete his stage without having to defeat him, but the other cards turn into doubles of him.
*** Sage of Time shows up on Day 6, hypnotizing civilians. If any of them make it all the way to him, he'll take their souls and you get a game over. You can wake them up to get them to start heading away from him, but if a demon gets them before they get away, same result. Later on the fight, the Sage will brainwash more civilians into entering.
*** Ikusa shows up with a swarm of powerful undead on Day 4. He revives the ones you defeat, and furthermore, you have to prevent any of them from reaching a pair of escape points while you battle him, then clean up after he's gone.
*** Also in Day 5, Nebiros. He appears surrounded by a lot of Vile demons with healing capabilities, meaning he can hide behind them and hit you from afar.
*** The Fallen Morning Star, Lucifer, is the toughest boss of them all, and is also available in the base game. While insanely difficult (infinite range, level 99, etc.), beating him does give you the ability to fuse him. Most people just take advantage of the fact that Recarm gives the revived the next turn to attack, and just suicide run him. Though your strategies are moot if he manages to get Megidoladyne off a couple of times, since every cast boosts its power until the 4th/5th is LETHAL. The first already does 500-600 on everyone!
** ''VideoGame/DevilSurvivor2'' has a whole slew of these. Ghost Q and Billiken are available in the first playthrough; the rest will require a NewGamePlus at minimum. Nebiros, Belial and Alice require you to purchase the perk that lets you fight them.
*** Ghost Q shows up at a time when you only have the MC in the party--you actually can get one other character into your party before engaging him, but he won't fight you. Also, if you defeat all of the other demons on the field before finishing him off, he'll run away.
*** Billiken is a fairly standard battle, except his battle is the first one in which you can crack Holy Dance, and unless you abuse the hell out of the movement skills, he's programmed to go straight for the Pazuzu that has it and one-shot it. He can also steal money from enemies; if he manages to deplete your wallet, he can hit you with Barrage Strike, which hits for a lot of Almighty damage.
*** The Sage of Time will fight you with mid-tier demons when you're far too underleveled to be able to equip any of the heavier-hitting moves in your arsenal.
*** Lilith sics a bunch of hypnotized civilians which you have to avoid killing with immensely strong demons, ''and'' her Temptation skill will wreak havoc amongst enemy leaders. Worse, any male leaders hit by Temptation will be charmed without fail, even with Null Mystic (the Barrier Auto Skill will stop male leaders from being charmed if they have it equipped). Female leaders aren't charmed just as unfailingly, but there ''is'' a chance Lilith can charm them anyway.
*** Beelzebub is a vicious BarrierChangeBoss with a nigh-flawless defense and incredible attack, with a continuous stream of overleveled {{mook}}s.
*** As a CallBack to his boss fight in the first game, Belial will regularly hit the entire map with Gomorrah Fire, so you and your demons need to, at least, Null Fire.
*** Nebiros will appear in a gaggle of undead and continuously summon more if you kill them, and BodySurf into them if you instead choose to go after him.
*** Finally, Alice isn't as difficult as Lucifer, but she does have Belial and Nebiros fighting with her, both with their signature tricks. Alice herself can easily oneshot entire parties with ''Die For Me!'', remotely drain them to death with Vitality Drain, revive Belial and Nebiros, and speed up their turns.
*** The UpdatedRerelease, ''Record Breaker'', gives you an option to fight the Ticos. One of the biggest bummer about this fight is that they bring back the dreaded ''Megidoladyne''.
* ''VideoGame/NeverwinterNights2'':
** Tholapsyx the red dragon, thanks to her size and fire attack; buffing the entire party (preferably with Energy Immunity: Fire and Stoneskin) and micromanaging spellbooks is almost mandatory, as opposed to the final bosses, whom you can just whack with sheer force if the party is well-equipped. The reward is 200,000 gold for your keep plus an insane amount of loot, including a cool weapon for paladins and clerics who bothered to take a certain quest in the keep.
** ''[[ExpansionPack Mask of the Betrayer]]'' has its own bonus boss, a seemingly harmless badger spirit that turns into a Gigantic Angry Badger of One-hit-kill Doom if you manage to anger it. Killing it nets one one of the only items in the game to grant permanent haste status (barring the time-consuming item crafting).
** Also in ''Mask of the Betrayer'', if [[MindHive One of Many]] is in your party when you meet the dead god Myrkul, they'll ask if they can eat the god's remains. Unfortunately, rather than eating souls outright like the PlayerCharacter's curse, One of Many adds consumed souls to its collective. Thus HilarityEnsues when [[AssimilationBackfire Myrkul overpowers One of Many and takes over]].
** In ''Storm of Zehir'', you can encounter One of Many on the world map, who will probably be impossible to beat the fist time you encounter it (you're thankfully not forced into a fight with it). However, due to the WideOpenSandbox nature of the game later on, you can return and fight it once you're sufficiently leveled. Beating it will earn you the Imarskarcana, a helmet with good spell resistance, the ability to summon a demon once per day and a few other perks. If you don't want to fight it, you also have the option to feed it your companions for experience points.
* ''VideoGame/TheWorldEndsWithYou'':
** Panthera Cantus is the toughest boss in the entire game. It has the highest attack power of all the Noise and two separate bodies; [[spoiler:a tiger on top and a lion on the bottom]]. The fight itself can be quite hectic and requires the player to pay absolute attention to what is going on in both screens.
** In addition, there are four "Boss Noise" on various days (Progfox, Grindcore Minks, Wooly AOR, and Goth Metal Drake), blue Noise symbols that lead to fights against ''much'' stronger Noise than average. For HundredPercentCompletion, you have to beat them all on Hard. Feel free to whimper.
** Additional Boss Noise symbols for every non-Bonus Boss except for the FinalBoss appear on various days after beating the game. This is more of a convenience for those going for HundredPercentCompletion, since you don't have to go through the entire chapter to fight the boss again, and can retry the fight if you didn't get what you were looking for, with the exception of the FinalBoss, which is annoying since that day has three bosses beforehand. [[spoiler:And, yes, as you may have feared by reading below, Reaper Beat and Taboo Minimimoto show up as Blue Noise as well. And, yes, you have to beat them on at least Hard in order to get all of the Secret Reports. [[RuleOfThree And, yes,]] you still need to beat Minamimoto, the harder one, on Ultimate to complete the Infinity + One Pin Deck.]]
** Unfortunately, some of these bosses were timed fights, so on your first time through, [[HoldTheLine you won if you managed to survive for 30 seconds]]. No such escape clause in the post-game, and many of these bosses are still intimidating, even having killed the final boss.

* ''VideoGame/IcewindDale II'' has two of these, both within the same chapter. The first is a [[spoiler:black dragon in the "Crossroads", which can be killed to close the teleport to Kuldahar.]] Players don't actually have to fight it, and can achieve their goal in a much easier way, but the difficulty of the battle alone makes it worth it for many players. The other boss is [[spoiler:the Six Lost Followers, in the Kuldahar graveyard. This is regarded by many to be the hardest fight in the game, because A) there are six different enemies to fight at once, B) they are several levels higher than your party, and C) because each has only a few specific weaknesses, being immune to all other forms of attack, and with the weaknesses being different between each member.]] Victory gives the player the Holy Avenger, the best weapon in the game. Unfortunately, this pisses off quite a few people itself, as the weapon can only be wielded by a Paladin, meaning that there is no reward for anyone without a Paladin in their party.
* The Gundam RPG ''VideoGame/MSSagaANewDawn'' has Ultima Gundam and Omega Gundam, made from a mix of parts from ''Anime/MobileFighterGGundam'' and ''Anime/MobileSuitGundamWing'' mecha respectively. Their names are obvious {{homage}}s to ''VideoGame/FinalFantasy'''s perennial Bonus Boss pair, Ultima Weapon and Omega Weapon.
* ''VideoGame/LiveALive'' features several ultra-tough hidden bonus bosses. The caveman chapter has King Mammoth, who offers a decent reward in the King's Fang, as well as the randomly dropped "Soda." The ninja chapter has Majin Ryunosuke, who can be beaten for a weapon that you can also get at the end of the chapter if you don't kill anyone, and Lord Iwama, who drops an item that can deal a decent amount of damage if used in battle. The final chapter has about five, four of which drop the most useful equipment in the game.
* ''VideoGame/ParasiteEve'' had a few in the [[BonusDungeon Chrysler Building]]. While most of the bosses are color swaps of the storyline bosses, the giant cockroach and giant bee were exclusive to the building. [[spoiler:The original Eve is at the very top of the building, and defeating her gets you a different ending.]]
* ''VideoGame/LostOdyssey'' has seven: Persona, King Kelolon, the Cave Worm, the Blue Dragon, the Holy Beast, Legendary Spirit Sorcerer Fu, and The Immortal One in the Backyard. Players with access to UsefulNotes/{{XBox Live|Arcade}} can get a new downloadable dungeon with an extra boss [[spoiler:Professor K, aka The Killalon]].
* ''VideoGame/GrandiaXtreme'', rather than a new and unique boss, gave you the chance to go back to the old dungeons after beating the final boss, and in one of them you can fight a super-powered level 200 version of a boss you already faced.
* ''VideoGame/MonsterRancher Advance 2'' features Ragnarok, a wandering special Dragon who only appears after beating the final boss. He will only appear to fight you once a year, and only if you have a specific kind of monster on your farm. If you're not prepared to fight him on the week he comes to visit, too bad for you! His stats are extremely high (especially considering when your monster can first fight him), and he's tough.
* ''VideoGame/TheLegendOfDragoon'':
** In the dungeon before the PointOfNoReturn, you are given the opportunity to fight the spirits of the three dragons you defeated. They drop some useful attack items, and they're also guarding chests containing powerful equipment.
** There's also the Poltergeist-posessed armor set in Fort Magrad, an optional section of the Snowfield on Disc 3 (you travel through this area on your way to Velwebb. Hint: the sword has an instant-kill attack and it always uses it at the character who manages to dispatch it.
** There's also the four Dragoon ghosts in Velwebb, and Magician Faust at Flanvel Tower, who is the most powerful enemy in the game. Beating him does get you a great reward though in the Phantom Shield along with 30,000 gold. Here's everything you have to go through to get to him, which definitely puts him in this trope by the above definition: Throughout the game, there is a side quest to collect a total of fifty stardust scattered throughout the continent. Every tenth stardust, when shown to the proper character, will give you a different item. The final item is a mirror that is required in order to face Faust. Faust is an insanely powerful Wingly who was second-in-command to Melbhu Frahma, but ends up being a dozen times more dangerous, possibly due to having been alive and studying/training for the entire time his "boss" has been asleep. You then have to find the entrance to Flanvel Tower, following a winding maze of teleporters just to get to the tower. If you do not have the mirror in your possession the first time you see him, he WILL kill everyone in your party with one blow a piece, and you will be unable to touch him. As it turns out, this first Faust is merely a projected image. The real Faust is able to cast his magic through the image even while being twice as deep in the dungeon. And so, obviously, you must finish the maze.
* ''VideoGame/RivieraThePromisedLand'' has Hades, the boss who only appear in the extra content section after you complete the game and obtained the Key to Hell from the Zombie Dragon in chapter 6. His Breakout does heavy damage, but he only attack once every 3 of your each character's turns (estimated), so if you keep healing yourself with elixer and attack him, he's a pushover. Of course, the final boss can has its HP brought down by 53% with [[InfinityPlusOneSword Fanelia]]...
* All the ''VideoGame/{{Geneforge}}'' games have an 'Expert' level dungeon with the toughest Bonus Boss in the game. Most of them generate repeated creations to add to their attack power, and traps that deal extra damage unless the player has the skill to disable them or at the least reduce their effect. The worst is the Titan of ''Geneforge 4'', which each time it was weakened to low health would shift to a new form, with a new set of attacks, defenses and vulnerabilities, requiring the player to have mastered a wide range of combat abilities. And of course, leaving the dungeon to rest also reset this Boss to its original form and strength.






* ''VideoGame/ManaKhemiaAlchemistsOfAlrevis'' had 5 Bonus Bosses in total: four that were cameos from other Gust games, and the fifth is a PaletteSwap of the TrueFinalBoss. Each of them are fought individually, but later three of them can team up for a sixth battle, which can be ''very'' difficult if the player's not prepared. The only saving grace for that battle is their common [[WeaksauceWeakness vulnerability to a certain character's]] ''[[WeaksauceWeakness normal physical attack]]''.
* While it's "only" a Mod, the ''VideoGame/KnightsOfTheOldRepublic Brotherhood of Shadow'' [[spoiler:has a flashback to Malachor V]]. You're stripped of all your gear, and [[spoiler:have to re-create the single-combat against Mandalore that ended the Mandalorian Wars]]. Comparatively, the canonical FinalBoss fight against Malak is nothing.
* ''VideoGame/{{Mother 3}}'' features several. First there is Lord Passion, who carries Duster's [[InfinityPlusOneSword Infinity Plus One Shoes]], Lil Miss Marshmallow guards a decent weapon for that point of the game, and the King Statue is just there for experience and is ridiculously easy if you know what to do.
* The Doppelganger in the ''[[VideoGame/DotHackGUGames .hack//G.U.]]'' games is optional, but is ridiculously difficult and gives some of the most powerful weapons in the games.


* ''[[Franchise/{{Naruto}} Naruto: Path Of The Ninja 2]]'' has the Kumite Dojo, which has many bonus bosses.
* ''VideoGame/ResonanceOfFate'' pits you up against [[spoiler:Sullivan and Rebecca]] at the end of [[BonusDungeon Neverland]]. Unlike many examples on this page, they are generally considered pushovers, especially compared to what you fought to get to them.
* ''VideoGame/TheSpiritEngine2'' has a variant: the bonus boss, Urtat Underval, is fought roughly halfway through the game rather than at the end. Another variant is that you fight him twice; [[spoiler:once as a human, and once as a hulking zombie]].
* ''VideoGame/SandsOfDestruction'' has plenty, including a few solo bosses involving Toppy, Kirie, and Agan.
* ''VideoGame/{{Ys}} VI: The Ark of Napishtim'' has Majunun, a blowfish-like creature that guards the Eldian Orb and will kill you in one hit the first time you can access it. Just finding it is a GuideDangIt, and to have a chance of winning at all, you need to nearly max out your EXP, which takes many hours, as all the enemies only give 1 EXP on the highest few levels.
* ''VideoGame/FossilFighters'':
** There is a ''huge'' slew of bonus bosses, one of which opens up before the final boss, and the rest of which appear afterwards, in the PlayableEpilogue.
** The lone bonus boss available before the game's end is Petey, a dino battler who demands to fight a team of three specific dinosaurs. If you take the time to grind those three specific dinos, he's managable, but if you're anything less than maxed, be prepared to hurt from it.
** But ''after'' the final boss? Both Saurhead and the [[TerribleTrio BB Trio]] reappear with "marathon battle" bosses, where you have to beat three of their teams with no break in-between. They're tough, and your reward is [[spoiler: the OlympusMons]] from waaay back at the game's halfway point. You can finally fight Dr. Diggins, though he offers up nothing but [[BraggingRightsReward bragging rights]] (and EXP, if you're looking to grind). You can fight a samurai who's been in the hotel room next to yours [[ChekhovsGunman for the entire game]], whose most notable trait is that his Trainer rank is [[UpToEleven one beyond "Master."]] Oh, and if you're feeling lucky, punk, you can go back to [[spoiler: the dinaurian spaceship]] and challenge [[spoiler: Duna, Raptin, and Dynal--all at once.]] And ''that isn't even all of them!''
** The sequel, ''Fossil Fighters Champions,'' follows suit. In addition to almost all of the important characters having high-ranked teams you can fight in the PlayableEpilogue, there's a ''bonus tournament'' that culminates in a fight against [[spoiler: Rosie from the previous game.]] There were also DLC bonus bosses--including a strange character named Ryne, who gives you a new legendary vivosaur for winning, and [[spoiler: Duna, Raptin, and Dynal again]].

* ''VideoGame/LegendOfLegaia'' has Lapis, who has insane attack power and can incapacitate a party member with a string of vicious attacks that deal upwards of 200% of the character's HP. Beating this boss requires either a lot of luck, hours of LevelGrinding, or using a very specific accessory setup. [[note]]Specifically, equipping the Luminous Jewel accessory. Since Lapis's attacks are Light elemental ([[GuideDangIt The game does not mention this.]]), using this accessory cuts his damage output in half and makes his attacks survivable.[[/note]]
* ''VideoGame/SailorMoonAnotherStory'' has [[spoiler:Esmeraude in the fourth chapter]]. Beating said boss gets you [[spoiler:a second Red Pupil]].
* ''VideoGame/MarvelAvengersAlliance'' has the Epic Bosses in certain missions, which only show up if you fight every battle and complete every deploy (which often require spending rare Command Points to recruit specific heroes) in that mission. The bosses offer stronger weapons and gadgets and higher chances of winning more Command Points as prizes for defeating them, compared to normal bosses.
* Even an RPG that is stripped down to its bare mechanics also has one. ''VideoGame/{{Parameters}}'' has the bottom rectangle (previously the second-strongest enemy in the game), which turns into a 9999 hp opponent with high defence and attack after beating the FinalBoss. Thankfully, it isn't really ''that'' difficult so long as you have enough life regeneration, but it does get tedious as it regenerates health quickly and can take a ton of punishment.


* A lot of bosses in any of the ''VideoGame/{{Neptunia}}'' games will be this trope. The strongest in ''VideoGame/HyperdimensionNeptuniaMk2'' is Delphinus without the DLC while a lot of people have a hard time against Gargoyle in ''VideoGame/HyperdimensionNeptuniaV''.
* ''VideoGame/TheLastStory'' has [[spoiler:Therius]] and [[spoiler:Gigamuruk]]. The first is a one-on-one DuelBoss who can only be challenged with Zael alone, in a callback to an earlier boss fight. The latter is fought at the conclusion of the game's running TournamentArc. In both cases, you have to wait until the PlayableEpilogue to look for them.
* Tyrant in ''VideoGame/{{Opoona}}''. He can actually be fought surprisingly early on, before the game's halfway point, and defeating him is required to [[RelationshipValues raise your friendship]] with a few [=NPC=]s. However, taking him on so early and ''surviving'' is another matter entirely.
* ''VideoGame/{{Robopon}}'' has a couple. In the original, you can rematch the first six Legends in Zero Tower post-credits. The second game has several, including Rena's restored-to-youth mother, the younger version of Nick D., the Robopon in Delica Castle's basement, and the W-King.
* ''VideoGame/AWitchsTale'' has a bonus fight with friendly vampire Loue, who suddenly turns not-so-friendly for the fight. If you win, you get a game-breaking doll.


* The Bonus Bosses in ''Videogame/TheWorldEndsWithYou'' are select blue Noise found during a scan. They are always in the same spot on the same chapter, and unlike the regular bosses, you are given the option to escape from the battle. Beating them on Hard or Ultimate is necessary for OneHundredPercentCompletion.
* ''VideoGame/SandsOfDestruction'' features Dark Kyrie, the protagonist's doppelganger spawned from his fear and doubt. He's entirely optional and can only be accessed by getting back inside the Temple of Light after it's been darkened (which [[GuideDangIt wasn't easy the first time]] and isn't any easier the second), but he drops his InfinityPlusOneSword, the Destruct Blade.
* ''VideoGame/{{Undertale}}'':
** Glyde, who only appears in the room with the door in Snowdin Woods, with a very low encounter rate.
** So Sorry, who appears in Hotland after unlocking all of the elevators near Sans' hot dog stand, but only at 8pm on October 10th.
** The Nintendo Switch version adds an optional boss fight with [[spoiler:Mad Mew Mew]], [[spoiler:a life-sized Mew Mew Kissy Cutie figurine possessed by the Mad Dummy.]]
** In the follow-up/{{Elseworld}} game ''VideoGame/{{Deltarune}}'', you get to [[GuideDangIt find]] and ultimately fight the locked-away [[spoiler:[[MonsterClown Jevil]]]], whose fight makes the FinalBoss look tame through sheer BulletHell and the difficulty of many of his attacks. Depending on how you defeat him, he'll either [[spoiler:give you the best armor]] or [[spoiler:the best weapon in the game.]]







* ''[[Videogame/NocturneRPGMaker Nocturne: Rebirth]]'' has a bonus WolfpackBoss consisting of three characters from another UsefulNotes/RPGMaker game, ''Cross of the World''. After beating them once, they'll be strengthened to match a maxed-level party.
* ''VideoGame/RakenzarnTales'' has a feature known as the Ultra Boss. You need a specific party member in your line-up when fighting a specific boss under certain conditions - usually having cleared a minimum number of quests. They're a pretty clear step up, but winning gets you a stat boost, bonus stats and a new piece of equipment that grants a party member exclusive move.
* ''VideoGame/{{Lunarosse}}'' has two post-game bosses. One is implied to be a GreaterScopeVillain for the creator's future projects and the other tied into the SequelHook.
* ''VideoGame/UncommonTime'' has one at the end of each BonusDungeon: [[spoiler:Altair]] at the end of Aubrey's Uncommon Time, and [[spoiler:Arietta]] at the end of Arietta's.

* ''VideoGame/LiarJeannieInCrucifixKingdom'' has the two elite Pleiades Knights, [[DualBoss Celaeno and Alcyone]], [[spoiler:who guard the exit of the kingdom and must be defeated to get the secret ending.]]
* ''VideoGame/{{MARDEK}}'':
** Chapter 2 has the Zombie Dragon, located in Social Fox Tomb, accessed after the first battle with Moric. It has ''11000+ HP'' and can inflict most [[StandardStatusEffect status effects]], though he goes down rather easily if you have Vehrn and Mardek equip a Silver Sword (Or replace Vehrn with Zach and have the boneslicer equipped) and have Quarry:Undead active.[[note]]Vehrn also has Smite Evil and Disrupt Undead, making him a better choice than Zach.[[/note]] Upon defeat it drops the Burial Sword, the best weapon for Deugan in the chapter.
** Chapter 3 has Annihilator:Karnos fought in the [[EldritchLocation Miasmal Citadel.]] In addition of starting with Haste, having ''[[MarathonBoss 66,000 HP]]'', can also [[BarrierChangeBoss change its element]] either when taking a turn or reaction to magic attacks in addition of hitting like a truck to the entire party without proper resistance. He can and will dispel Haste and/or shields if you have them up.Defeating him gives you the Guardian Claw, the best weapon for Solaar in the chapter, Scarab of Fury and is also required to fight the boss below.
** Annihilator:Animus, which, despite having lower HP than Karnos and can't change elements, is actually ''even stronger''. Fought in the [[SpiritWorld Dreamshrine]], it starts the battle with Haste and Regen, has 50% resistance to most elements (Except Fig, which it's very weak to), can dispel Haste and shields like Karnos, very high physical defense, can deal Thauma damage, has HP percentage Aether attack and puts up shields on low HP. Defeating it gives Sorcerer's Soul and Scarab of Protection.
* ''VideoGame/{{LISA}}: The Painful RPG'' has a giant man who goes by "Satan,"[[note]]His actual name is Mike, which he tells you when he's dying[[/note]] found inside a truck on an off section in the Eternal Wrestling Championship that links Area 2 and 3. The keys to his truck are guarded by the Joy Mutant "Beady," itself a difficult and optional boss. He is one of the hardest bosses in the entire game, having a lot of health and access to an instant-kill move, but he drops one of the best equipment pieces as a reward. To emphasize his difficulty, he has an ominous buildup to him, with the NPC outside his valley telling Brad that nobody who has gone in the "Devil's Machine" (his truck) came out alive, the screen tinting red as Brad gets near the truck, and a mild JumpScare-honk playing when in front of it.
* ''VideoGame/SacredEarthPromise'' has [[spoiler:an unnamed shadowy version of Isole]] in Icefall Labyrinth, who is on a similar level of difficulty as the FinalBoss, Forneus.

** ''Yo-kai Watch 2'' brings back the Infinite Inferno with the same bosses, but also adds the Divine Paradise, which has palette swaps of several bosses of the main story of said game -excluding Gutsy Bones and Eyeclone, whose recolors are featured elsewhere, and Meganyan, with no recolors at all- and has [[spoiler:Kat Kraydel as an unique boss, as she is the cause the summer is seemingly extending infinitely, as Hovernyan states at the beginning of the post-game.]] The second bonus dungeon is the Mystery Way, which features palette swaps of Gutsy Bones, Eyeclone, and Hans Full, though the three versions of the game must be connected in order to fight all four of them. In addition to bringing back Chirpster and Duwheel as well, the aforementioned Hans Full, Retinado (as part of the Gates of Whimsy sidequest) and Mallice (at the end of the Infinite Tunnel) appear as additional bosses. The 2.0 update and the third version adds Rubeus J, Hardy Hound and [[CreatorCameo Hinozall]] in the Psychic Blasters mode, and Bronzlow, Teastroyer, Infinipea, Headsteam, and Kabuking in additional sidequests and locations.

* ''VideoGame/OctopathTraveler'' has four shrines in the four corners of the world, where you can gain access to four advanced hero classes by proving your worth to the gods that guard them, along with a number of strong bosses findable by exploring caves and dungeons unrelated to the main plotlines. And in a very amusing twist, after beating all eight main scenarios then finding and fulfilling a newly unlocked chain of sidequests, you unlock the toughest challenge in the game: [[spoiler:the TrueFinalBoss linking all plotlines together, Galdera the Dark God. Looks like the simplest way to fix the "secret bonus boss is stronger than the final boss for no reason" problem is to make them one and the same.]]
* ''VideoGame/TheWorldIsYourWeapon'': Defeating the Demon Lord is not necessary to get the first ending, but beating him is necessary for the third and fourth endings. He and the FinalBoss can also be fought in rematches so that the player can capture them. In version 2.40+, Weaco will have to fight [[spoiler:a third version of the Demon Lord to get the secret ending]].

* Finish ''[[VideoGame/{{Parodius}} Gokujou Parodius]]'', and you get to fight your way through a "bonus stage". Who awaits at the end? [[NinjaPirateZombieRobot A fire-spewing laser-shooting warmachine-deploying robotic penguin]]. It's as awesome as it sounds.
* ''VideoGame/ArmedPoliceBatrider'' has a crapton of Bonus Bosses, all of which appeared in the ''Mahou Daisakusen'' series and ''VideoGame/BattleGaregga''. Said bosses include Bashinet, the Stage 1 boss of ''Mahou'', and [[ThatOneBoss Black Heart]], the Stage 5 boss of ''Garegga'' that, thanks to the stage edit feature, you can [[WakeUpCallBoss fight as early as Stage 2]].
* ''[[VideoGame/DonPachi DoDonPachi Dai-Fukkatsu]]'' has the six normal bosses of ''[[VideoGame/DonPachi DoDonPachi]]'' (Suzaku, Senkou, Kakou, Raikou, Rankou and Ryuukou) as bonus mid-bosses, triggered by fulfilling certain conditions.
* ''VideoGame/{{Hellsinker}}'', as with [[VideoGame/ArmedPoliceBatrider Batrider]] and [[VideoGame/BattleGaregga Garegga]], has loads of secrets. Defeating the Scarlet Queen will result in a secret form of the boss that [[BulletHell unleashes hell]] for 15 seconds, then disappears. The secret form can be easily triggered if the player has the game at a high [[DynamicDifficulty rank]], but it can also cause quite a surprise by randomly appearing under normal circumstances. If that happens, [[https://www.youtube.com/watch?v=X00wKV3SYIE you're in for a world of hurt]].
* ''VideoGame/AbmneshiTheProphecy'' has, in addition to a collection of {{True Final Boss}}es, a secret and entirely optional stage containing Sirisai, who's about as hard as the FinalBoss.
* In the [=PS2=] remake of ''VideoGame/SpaceHarrier'', continuing to fire at the end of Stage 19 results in the game continuing for four more stages, with twin fire dragons Haya-Oh awaiting at the end of #22.
* The giant space worm of ''VideoGame/EventHorizon'', which can be [[RandomEncounter randomly encountered]] in Beacon events. It sends out a [[HordeOfAlienLocusts Horde Of Alien Locusts]] at the player in addition to normal attacks, and [[SubsystemDamage you have to destroy its tail segments]] before you can deal any meaningful damage to it. [[spoiler: The same enemy appears later on as the boss of one of endgame factions.]]

* The ''Videogame/TraumaCenter'' series has the X operations, which have you performing [[EpilepticTrees simulated/imagined/secret/God-knows-what]] operations involving NintendoHard variations of GUILT, Stigma, or Neo-GUILT.

* Two of them are available in the combat sequences-filled DatingSim ''VideoGame/MitsumeteKnight'' : [[spoiler: Zeelbis the Bloody]] and [[spoiler: Salishuan the Spy]] of the Eight Generals of Valpha-Valaharian, the main enemy squad of the game. While not a storyline-related boss unlike the other two, [[TheCameo Sparkster]] of the ''VideoGame/RocketKnightAdventures'' series count too.

* ''VideoGame/LuminousArc2'' has the reoccurring boss for the optional ThatOneSidequest Spa Battle series, [[spoiler:[[VideoGame/LuminousArc Vanessa]]. Not only does she have high strength and can use a stat-boosting spell, she's also joined by respawning and stat-specialised [[MascotMook Kopins]], who only exists to wear down your party. Pity the unfortunate player who didn't bring any anti/nulling fire Lapis and suffers from either her attack, spells or [[LimitBreak Flash Drive]]. She'll get stronger each time you face her, until the sidequest is finished]]. Beating this multiple of times with {{New Game Plus}}es is required for the HundredPercentCompletion.
* ''VideoGame/FinalFantasyTactics'' gave us Elidibs and the Zodiac summon.
* In the postgame of ''VideoGame/YuGiOhMonsterCapsuleGB'', you can duel Joey, Tea, Tristan, Ryou, Grandpa, Pegasus, Bandit Keith, Shadi, Yami Bakura, and a freed Seto Kaiba. The latter two have the toughest monsters in the game.

* By the same token, nothing in ''VideoGame/DwarfFortress'' says you ''have'' to find the [[ItWasHisSled Hidden Fun Stuff]]. Or [[OurAngelsAreDifferent the Vaults]], for that matter, if you're an Adventurer instead. Both will give you utter hell even by the game's standards.

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* ''Franchise/TheLegendOfZelda'':
** ''VideoGame/TheLegendOfZeldaALinkToThePast'':
*** The Four Sword Links in the remake on the UsefulNotes/GameBoyAdvance. Each Link had some abilities that Link could use, such as the Hurricane Spin, the Magic Cape, etc. Beating them was purely for bragging rights (though it did lead to a new ending).
*** In the remake, Helmasaur King is a Mini-Boss in the Palace of the Four Sword. This one is more durable and it can regenerate its mask; what's more, it can summon Helmasaurs to impede Link, has to be hit with a Light Arrow before Link can strike it with his sword.
*** Arrghus is another Mini-Boss from the Palace of the Four Sword. This one replaces the Arrgi with regular Bari (that instantly electrify themselves once they get hit with the Hookshot), and summons Kyamerons in its second phase.
*** Mothula is the third Mini-Boss in the Palace of the Four Sword. This one is much faster, has a Doppleganger Spin, and can summon bees to attack.
*** Blind the Thief is the fourth Mini-Boss of the Palace of the Four Sword. With a side bit of PuzzleBoss: whenever it gets decapitated, Link must swat the head back to its own body to make Blind vulnerable again.
** The UpdatedRerelease of ''VideoGame/TheLegendOfZeldaLinksAwakening'' for Game Boy Color featured a BonusDungeon based on color. The boss of the dungeon wasn't more difficult than the other bosses, but you could only enter the dungeon if you knew the color of the stalfos' clothes at the entrance. There were also a number of color-based puzzles that would be frustratingly difficult if you managed to get in anyway.
** ''VideoGame/TheLegendOfZeldaSpiritTracks'' has [[spoiler:Dark Link]] at the end of [[BossRush Take 'Em All On]]'s final level.
** ''VideoGame/TheLegendOfZeldaALinkBetweenWorlds'': Once you've completed all the [=StreetPass=] challenges, you're able to fight the bonus boss of that game. [[spoiler:It's Gramps, the curator of these [=StreetPass=] challenges. He originally set them up just so he can find and fight someone stronger than him.]]
** ''VideoGame/TheLegendOfZeldaBreathOfTheWild'':
*** Lynels [[BossInMookClothing aren't even considered bosses by the game]], but every fight with one is difficult. You are only ever needed to encountered one once in the game, and even then you are not required to beat it (and can even skip it entirely if you find another way to obtain Lightning Arrows). They are the most difficult reoccurring [[BossInMookClothing basic enemy]] in the game, and for a while the most powerful variant, the [[LawOfChromaticSuperiority Silver Lynel]] (who has more health than the ''final boss'' of the game) can only be encountered in the half-destroyed Coliseum, before other Lynels start to [[LevelScaling scale up to Silvers]]. [[HarderThanHard Master Mode]] of the game introduces an even stronger version of the Lynel, the [[GoldColoredSuperiority Golden Lynel]]!
*** The Champions' Ballad DLC is an involved quest administered by one of the Sheikah monks, mirroring your journey in the main game by adding new trials to the key areas on the map. After going around Hyrule and completing several tests, a new dungeon opens up. [[spoiler: The monk, Maz Koshia is at the end, and looks like any of the other inanimate mummified monks, giving the typical speech once Link reaches the end of a shrine. But then he starts ''moving'', tells you he has a final test, and teleports you both into a boss arena--he is your opponent. Maz Koshia turns out to be the most challenging boss in the game (more than ''[[FinalBoss Calamity Ganon]]''), borrowing from many previous bosses and tough enemies while adding tricks of his own. For a shriveled mummy, he's pretty strong, with a lot of health, hard-hitting attacks, and multiple phases that keep you constantly on your feet. Hearts, armor, food buffs, and the upgrades to your Champion powers obtained during the DLC certainly help, but even so, they still don't make him easy.]]

* ''VideoGame/IllusionOfGaia'' has Solid Arm, [[LegacyBossBattle a boss originally from the first game in the series]], ''VideoGame/SoulBlazer'', who's [[GuideDangIt only fightable]] if you [[GottaCatchThemAll collect all fifty Red Jewels]].

* ''VideoGame/{{Aquaria}}'' has a number of optional bosses, but many consider Simon Says to be the most interesting. He's well-hidden, and you don't actually fight him -- instead you play, well, [[ExactlyWhatItSaysOnTheTin Simon Says]], with a very useful third cooking slot as your reward for playing well.
* ''VideoGame/{{Okami}}'' has the [[spoiler:Bandit Spiders and the Kusa Five]].
* ''VideoGame/BloodstainedRitualOfTheNight'': All of the Bonus Bosses in this game are manifestly more difficult than the final boss if fought normally.
** Finding the Carpenter's Key unlocks a fight with the Master Carpenter.
** Finding the Millionaire's Key unlocks a fight with Millionaire's Bane, a possessed slot machine.
** Finding the Warhorse Key unlocks a fight with Revenant, an {{Expy}} of [[VideoGame/CastlevaniaRondoOfBlood Richter Belmont]].
** Once you reveal 99% of the map, O.D. will have a new book available in the library called the Tome of Conquest that he will point out is especially valuable. If you take it with you into the final area, he will fight you for it. If you beat him, you can borrow all of his books at once.
** Anyone who purchases the Website/{{Kickstarter}} Edition of the game gets to challenge an extremely difficult [[CreatorCameo secret boss]] for a shot at acquiring the [[WhipSword Swordwhip]].
* ''VideoGame/IttleDew'' has one at the end of the [[BonusDungeon Master Cave]]. Oddly, it's the one boss you beat through brute force rather than [[PuzzleBoss some kind of puzzle]].

* ''VideoGame/CaveStory'' has G-CLONE, fightable in the removed Wind Fortress that was restored in the Steam and 3DS eShop versions as a bonus area.
* In ''VideoGame/ActRaiser 2'', enter the password "Xxxx Yyyy Zzzz" to fight the final boss from the first game with the second game's mechanics, who [[NintendoHard takes several steps up in difficulty]] from the first game, as well as the final boss from the second.

* The Red Dragon features as a Bonus Boss in both of the ''VideoGame/DungeonsAndDragons'' {{Beat Em Up}}s.

* Via ''VideoGame/AsurasWrath'' DLC, two Bonus Bosses that have nothing to do with the main game story are [[Franchise/StreetFighter Ryu and Akuma]], who become Evil Ryu and Oni respectively.
* The doujin game ''VideoGame/{{Grief Syndrome}}'' has Oktavia von Seckendorff, an optional sixth witch who can be fought [[spoiler:at any point as long as Sayaka is dead]]. This already-difficult fight is made harder by the fact that [[spoiler:you can't use Sayaka, who is generally considered the best character, against her -- as anyone who's seen ''Anime/PuellaMagiMadokaMagica'' to the end knows, Oktavia is the result of Sayaka becoming a witch]].

* ''VideoGame/NoMoreHeroes2DesperateStruggle'' has Kimmy, a school girl with an [[{{Yandere}} unhealthy obsession over Travis]]. You only fight her if you don't go back to the Motel between fights with Charlie and Matt, making her the only assassin in the series who truly fits this Trope.

* ''Franchise/MortalKombat'' is the TropeMaker:
** The [[VideoGame/MortalKombat1 first game]] has Reptile as a secret boss. There is [[LuckBasedMission a very small chance]] that he will appear before the fight begins and give you clues on how to find him (ex."Look To La Luna"). You can only fight him if, on the fight at the Pit stage, you don't block, get a [[FlawlessVictory Double Flawless]] on your opponent, and finish them with a Fatality. Furthermore, [[LuckBasedMission there must be a ghost floating in front of the moon]]. If the conditions are met, the screen will flash with the words "You have found me, now prove yourself!" appearing, whereupon you will be taken to the Bottom of the Pit to fight him.
** ''VideoGame/MortalKombat2'' continued the tradition with Noob Saibot, Jade, and Smoke. Noob Saibot appears only if you win 50 battles consecutively. Jade appears if, on the fight before the question-mark box, you only use the Low Kick button to defeat your opponent (can be done on any round). Smoke is the most difficult to get, as you have to make Dan Forden appear and say "TOASTY!" while fighting on the Portal stage, then hit Down + Start while he's on the screen.
** ''VideoGame/MortalKombat3'' had Smoke as a hidden boss via one of the 11 hidden treasures of Shao Kahn that you can access after beating the game, as well as Noob Saibot. ''Ultimate Mortal Kombat 3'' added Mileena, Ermac, Classic Sub-Zero, and Human Smoke. ''Mortal Kombat Trilogy'' added Chameleon and Khameleon, who were all the male and female ninjas rolled into one, respectively. You can also fight every single one of these characters via the Kombat Kode system.
* ''VideoGame/PunchOut'':
** The Wii game has Franchise/DonkeyKong. He can only be encountered during the final segment of Story Mode (Mac's Last Stand), and it's not required to defeat him as the game only truly ends with [[spoiler:Mac's retirement from boxing]] after three defeats (in fact, merely facing DK once is enough to have him available in Exhibition Mode).
** ''Super Punch-Out'' for the SNES has the boxers of Special Circuit (led by Nick Bruiser, the TrueFinalBoss); the circuit itself has to be unlocked by winning the first three circuits (Minor, Major and World) without suffering a single defeat.
* ''Franchise/StreetFighter'':
** Akuma is usually a bonus boss in the games where he isn't the TrueFinalBoss, particularly in ''[[VideoGame/StreetFighterII Super Street Fighter II Turbo]]'', ''[[VideoGame/StreetFighterAlpha Street Fighter Alpha]]'', ''[[VideoGame/StreetFighterAlpha Street Fighter Alpha 2]]'' (as Shin Akuma), and ''VideoGame/XMenChildrenOfTheAtom''. The former is notable in that even if you're playing as a character whose final boss is supposed to be Akuma (like Ryu or Gen), you will simply fight Shin Akuma first and then you'll face the regular version of him.
** The CPU version of Dan also served this role in the first ''VideoGame/StreetFighterAlpha'', as did Q in ''VideoGame/StreetFighterIII: 3rd Strike''.
** In ''[[VideoGame/StreetFighterAlpha Street Fighter Alpha 2]]'' and ''VideoGame/StreetFighterIII: 2nd Impact'', each character has a specific rival who can only be fought if the player manages to fulfill certain conditions without losing a single match.

* Baiken, in the original ''VideoGame/GuiltyGear'' for [=PS1=]. In order to get to her, you had to beat the game as Sol or Ky, without using any continues -- once you get to her, though, you can try to win as many times as you like, and if you do, you unlock her as a playable character. Considering the extreme difficulty of defeating Justice the first time, and the first game's broken instant-kill mechanics, this was quite a task beyond the calling of most casual players.
** ''Slash'' and ''Accent Core'' also added in Order Sol, a past version of protagonist Sol Badguy, as one too. Fighting him in the latter requires having half of your victories (depending on the number of rounds set) be Overdrive/Instant Kill finishes before facing I-No; after which she will then teleport them to the past to fight him, which will no doubt end poorly considering how [[SNKBoss overpowered he is]]. Fortunately, unlike Baiken above, Order Sol is available to use from the start so you don't have to subject yourself to such cruelty to get him.

* ''[[VideoGame/CapcomVsSNK2MarkOfTheMillennium Capcom vs. SNK 2]]''. Bison and Geese (chosen randomly). Originally the main bosses from its previous installment, they will interrupt you before heading to the final match without any cutscene. To face them you must have at least 800 GP, never let your opponent achieve 5 First Hits, and finish at least 2 matches with a Custom Combo or Super Combo finish. Defeating them is one of the requirements in order to face [[TrueFinalBoss The True Final Match]] after your next match.
** ''VideoGame/SNKVsCapcomSVCChaos'' has Princess Athena and Red Arremer.
* ''VideoGame/SuperSmashBros'':
** ''[[VideoGame/SuperSmashBrosMelee Melee]]'' has Giant Kirby, who appears in the fifth stage of Adventure Mode if the group of smaller Kirbies is beaten in 30 seconds or less. Giga Bowser also appears as a bonus boss if you clear Adventure Mode quickly enough; and while he fights exactly like Bowser, aside from being bigger and stronger, you can't grab Giga Bowser to throw him off the stage.
** In ''[[VideoGame/SuperSmashBrosBrawl Brawl]]'', extra doors appear in three stages after you beat Tabuu; going inside them will pit you against Toon Link, Wolf, or Jigglypuff, depending on the level. However, you only have one chance to defeat them and their AI is much more aggressive than the characters you fought previously.
** In all games from ''Melee'' onward, Crazy Hand will join Master Hand as the final boss of Classic Mode if the player can get up the ladder fast enough while playing on a specific difficulty.
** In ''[[VideoGame/SuperSmashBrosForNintendo3DSAndWiiU Smash 4]]'', if the player is playing on a difficulty 3.0 or higher, your final opponent will be both Master Hand and Crazy Hand, however things get weird from here. If the player is on 5.1 or higher, they will be surprised when Master Hand and Crazy Hand blast apart, forming the various forms of Master Core. on 5.1, they will be attacked by Master Edges, at 6.0 they will get fought by Master Beast, then Master Edges. At 7.0, first Master Giant, then Beast, then Edges. No matter which difficulty, after beating the forms, you will then face Master Shadow, a duplicate of your current character. Finally, if you're on the Wii-U version and are playing at 8.0 or higher, you will then be attacked by Master Fortress, which is essentially a living stage requiring you to defeat four weakpoints while being accosted by various enemies. After all of that is done, Master Core will reveal itself, and if not defeated in under a minute, will instantly K.O. the player if they fail to dodge its attack. If the player defeats the orb or survives the attack (either by dodging or having more lives) then the battle is ''finally'' over.
* In ''VideoGame/SoulCaliburIII'', the arcade and Tales Of Souls modes will almost always be fought against Zasalamel's demonic form, Abyss, but an even stronger opponent called Night Terror can be fought. Night Terror will replace Abyss if the player encounters and defeats Olcadan before arriving at the cathedral where the last few battles take place. Night Terror can also be fought in the 'Final Battle' mission of the game's challenge mode.
* The ''VideoGame/VirtualOn'' series has several of these, some exclusive to certain versions.
** In the first game, if you win all your battles by Time Over, you'll get a Warning message and then enter a special battle with Jaguarandi, a mutated version of Raiden that varies each time you fight it. When you first fight it, it's about the size of a Raiden or a Belgdor, and its color is the opposite color of your mech. If you continue against it, [[BaitAndSwitchBoss it changes to a miniature toy-sized version that is colored purple, and its armor weakens severely (so much so that a close range attack from Apharmd will kill it instantly), and if you continue again, it can be killed in 3 hits by Temjin's Beam Rifle!]] In the Japan-only [=PS2=] version, if you beat all 8 virtuaroids in under 30 seconds, [[TrueFinalBoss you will hear a special chime and fight the original Fei-Yen instead of Z-Gradt]]. This version of Fei-Yen is always in Hyper Mode, but its armor is not weakened and its attacks are more powerful than the regular Fei-Yen.
** The sequel, ''Oratorio Tangram'', has Ajim -- a crystalline, transparent virtuaroid. To fight him, you must win at least one battle in your run with a Time Over. Once this is done, he will appear randomly at any time, even as late as the Raiden fight, [[DeathFromAbove crashing down on your opponent and destroying them]]. His stats are beyond mortal comprehension, meaning that he's faster and stronger than all other virtuaroids, and all damage done to it is lessened to roughly 5/8 of the usual. Oh, and you can't beat him via Time Over either -- if you try and do this, you will lose automatically. Encountering him automatically unlocks him for regular play in the later revisions, but on the Dreamcast version 5.45, he was only playable by beating him, then beating the game, and holding both Turbo buttons on the Random select box on the latter half of each month. And when you play as him, he has the weakest armor in the game, and to make matters worse, his health drains by 2% every second.
** ''FORCE'', the 3rd installment, has Shadow versions of your team that you can fight by, once again, getting Time Overs. These Shadow mechs are manifestations of a virus in the system, taking the forms of your mechs and making them much stronger than the normal version. Jaguarandi also returns, but as the default mid-boss, and this time it becomes '''LUDICROUSLY HUGE''', taking up over half of the arena. It's also a mutated Guarayakha now instead of a Raiden, trading in most of its long range advantages for godlike close range combat tactics. Ajim also appears, with a female version of it called Guerlain, but as the final boss, and utilizing completely different moves than before.
* ''Galaxy Fight'' and ''VideoGame/WakuWaku7'', the two fighting games made by Creator/{{Sunsoft}} for the UsefulNotes/NeoGeo, shared a common bonus boss named "Bonus-Kun", a punching bag (from "[[PlanetOfHats the Punching Bag Planet]]") with a limited moveset who parodies [[Franchise/StreetFighter Ryu]]. In ''Galaxy Fight'', [[DidYouJustPunchOutCthulhu after you defeat Felden]], you get to fight a final Bonus Boss in the form of Rouwe, an old man dressed in a karate gi.
* ''VideoGame/SamuraiShodown 2'' had a very tough Bonus Boss in Kuroko, whom you could either fight by meeting certain conditions, or just randomly after stage 3.
* ''VideoGame/OneMustFall'' has a few.
** In the One Player story mode, there's Fire and Ice. To take on Fire, you need to be playing on at least the hardest non-hidden difficulty, beat your opponent on the Fire Pit arena, do a destruction on them, and enter a robot-specific code. If playing on the very hardest difficulty, beat Fire and do the destruction and code again and you can fight Ice. These two are extremely hard to beat, but the devs reward you generously for doing so. Normally, the end of round bonuses on the hardest difficulty are 400,000 points. For Fire, they're 2 million points, and for Ice they're 20 million points. Good luck getting a perfect round against Ice. The only way to not take any damage from him is to not take any hits ''at all'', as he can still damage you even when blocking.
** In the tournament mode, there are various unranked challengers in each tournament. All of them are hard, and most require you to be playing on the hardest difficulty. If they're going to show up, they'll challenge you after doing a destruction on some other opponent. There's at least one occasion when one unranked challenger will challenge you after beating another unranked challenger, too.
* ''VideoGame/BloodStorm'' had several of these, all of them {{Palette Swap}}s of your main characters. Unlocking most of them was both fun and [[GuideDangIt ridiculously frustrating.]] For example, one of them required you to knock down a stalactite in one stage using projectiles, so that it falls down a pit. Then, you have to jump down, land on the small platform, and then you'll be able to fight the boss. Another required you to drop your weapon, and then perform the "pick up" command so that you touch the center of a summoning circle. And so on.

* ''VideoGame/{{Tekken}} 2'' has Roger the kangaroo, who appears in the fourth stage if you beat the third stage with low enough health to get a "Great!" from the announcer. Beating him and the rest of Arcade Mode will unlock him and his MovesetClone Alex, who is a dinosaur.
* In ''Tekken 6'', there's Nancy. She's one of several [[HumongousMecha giant robots]] developed by the Mishima Zaibatsu, perhaps to combat [[BigBad Azazel]], who [[Series/MightyMorphinPowerRangers is finally free after 10,000 years.]] Her appearance is sort of a BigLippedAlligatorMoment in that you get rewards for beating her but if you don't, it has absolutely no bearing on your progress and you don't get the option of fighting her again without restarting. [[spoiler:She is playable, but only in one level of Scenario Campaign.]]

* ''Franchise/BlazBlue'':
** ''VideoGame/BlazBlueCalamityTrigger'' the only way to fight Unlimited Ragna is to go through [[NintendoHard Score Attack Mode]] or to play through arcade mode finishing each opponent with a Distortion Drive (the TrueFinalBoss method). ''[[VideoGame/BlazBlueContinuumShift Continuum Shift: Extend]]'' features "Abyss Mode", where a special version of Unlimited Ragna appears at [[NumberOfTheBeast Depth 666]]. The first thing you'll notice is that he'll already be across the screen in a few short frames, making him more annoying to fight than Taokaka in terms of speed.
** ''[[VideoGame/BlazBlueContinuumShift Continuum Shift: Extend]]'' added Unlimited Mars mode, which is essentially a gauntlet of bonus bosses. It's a straight run of ten characters, but all in their Unlimited versions which have buffed stats and crazy new move properties/moves. ''[[VideoGame/BlazBlueCentralFiction Central Fiction]]'' replaced this with Grim of the Abyss mode, which is effectively the same thing.

* ''Vampire Savior'' has Oboro Bishamon, the man himself, rather than the armor. ''VideoGame/{{Darkstalkers}} 3'' makes him playable.

* If you manage to beat ''[[VideoGame/TheKingOfFighters The King of Fighters: Maximum Impact Regulation A]]'' without using any continues and with enough Super Finishes, you'll get to fight [[GuestFighter Makoto Mizoguchi]] of ''VideoGame/FightersHistory'' fame.

* ''VideoGame/GrimDawn'' has the bosses of the four challenge dungeons, each found at the end of a long multi-level dungeon that must be cleared in one run without dying. There are also the Nemesis bosses, who only start spawning once you have maxed out your infamy with their respective faction. All of the above have exclusive Monster Infrequent items only they can drop.

* ''[[Website/GaiaOnline zOMG]]'' features the Landshark, which appears semi-randomly in Gold Beach. The Landshark is one of the only charge level 10 (max CL) monsters in the game, and features insane attack power, extremely high HP, and attacks that can take up almost the entire screen. If you see one, running is advised. An update nerfed the Landshark to more manageable levels. (It's now only CL 7). However, a gamut of new bonus bosses were added in its stead, as well as "Challenge" versions of all Instance Bosses. While none of these (with the exception of [[spoiler:Sea Witch and Labtech X]]) are CL 10, they have the added difficulty of only being vulnerable to individuals below a certain charge level. Meaning that players wishing to battle Airshark need to suppress their CL to level ''2''.

* ''VideoGame/CityOfHeroes'' has the Army of Me badge, unlocked via a special option in a Villain Side story arc. The mission? [[OneManArmy Beat a full team]] [[CloningBlues of yourself]].
--> ''You don't understand the math behind it, but you're pretty sure you're equal to or greater than eight of yourself.''
* ''VideoGame/FinalFantasyXI'' has the Notorious Monsters. The most, well, notorious of these are the Pandaemonium Warden, a SequentialBoss [[UpToEleven with 10 different forms]] who has to be beaten in 2 hours[[note]]the time limit was instated after a group battled him for ''[[MarathonBoss eighteen hours straight]]'' and ''still'' didn't win[[/note]], and Absolute Virtue, who has such [[https://www.reddit.com/r/ffxiv/comments/apld7n/absolute_virtue_what_ffxiv_players_should_know/ absolutely obscure]] mechanics that it was never beaten fairly until the rising level {{cap}} made it irrelevant.
* ''VideoGame/FinalFantasyXIV'':
** The game features plenty of end-game contents, some of which are either BonusDungeon while others are this, or both. Some of the content is loosely tied with the overall plot; completing them isn't necessary to advance the story. Hard Mode and Extreme Mode versions of the Primal fights are available to tackle, along with the bosses in the intermediate 24-man, and hardcore 8-man, raids, with the latter having a Savage version which brings more mechanics to challenge the team.
** ''The Unending Coil of Bahamut'' takes the cake as the first raid content to be pegged at the '''Ultimate''' difficulty. And it certainly doesn't disappoint, as it consists of embellished and fiercer version of the final turn for each part of the Binding Coils of Bahamut (Turn 5, 9 and 13), with all of them [[TurnsRed pulling all their stops at the get-go compared to regular Coil]], culminating with Bahamut Prime dropping [[ColonyDrop a mini-Dalamud]] to the stage and sends powerful shockwaves that will wipe the party if not mitigated with a Limit Break from a tank-role player. And then after the Tera Flare phase, Bahamut Prime proceeds to [[TurnsRed unleash its inner rage]] in its golden form, and starts to spam Akh Morn and Exaflare, and if it was not defeated quickly it will begin to spam Morn Afah (appropriately means "eternal death" in dragon language) until the whole party is wiped out. Clearing the Unending Coil demands a great amount of team synergy and their proficiency with the battle mechanics much more than any other raids before it, to the point that Deltascape 4.0 Savage (the highest-level raid content when Unending Coil was released) is a mandatory requirement ''just to enter it''. Furthermore, at the time of its release, none of the participants were able to clear it within the first week, with the world first clear happens on the 11th day after the release.
** The Weapon's Refrain is just as difficult. Just like the Unending Coil, this fight is a gauntlet against several bosses in a row; Specifically: Garuda, Ifrit, Titan, Lahabrea, and the Ultima Weapon. In addition to the moves they usually do being supercharged, the whole encounter is a [[PuzzleBoss giant puzzle]], as the party needs to ''[[ViolationOfCommonSense hit the Primals with their own attacks to power them up]]'' in order to obtain extra [[LimitBreak Limit Breaks]] for use against Lahabrea, and failing to do so will ''always'' result in a wipe. A Level 3 Caster Limit Break is required to destroy several [[ActionBomb self-destructing Magitek Bits]] before they explode, a Level 3 Healer Limit Break is needed to cleanse an otherwise uncleansable Doom debuff Lahabrea places on the party, a Level 3 Melee Limit Break is needed to finish off Lahabrea before he casts Dark IV to wipe the party, and a Level 3 Tank Limit Break is needed to survive the Ultima Weapon's opening attack of Ultima. Then, once the Ultima Weapon fight begins proper, ''dying to it causes it to build up its own Limit Break faster''. If the Ultima Weapon reaches 100% charge, it begins dragging players one at a time into the air and blasting them with an attack that deals 999,999 damage ''and prevents their corpses from being targeted, in turn preventing them from being raised''.
** Memoria Misera is a very difficult boss. Based on a previous solo instance boss battle against [[spoiler:Emperor Varis (or rather, a highly embellished version of him)]], much of the difficulty from the fight comes from mechanics that require precise synchronized placement of all party members to avoid stacking damage. As the fight moves into its second and third phases, a pair of DPS checks come into play as well, the first requiring both tanks to interacte with designated spots on the map to catch a massive sword beam and succeeding in the ensuing [[ActionCommand Active Time Maneuver]] to survive (emphasis on ''both'' tanks: if one of them is out of play, the other will quickly die and the party will wipe) while the party takes continuous damage, making it a taxing healer check as well. The second DPS check is accompanied by two attacks, one that requires the players to stack to mitigate damage and another that requires the players to spread out to avoid getting hit repeatedly. Each new phase also forces players to contend with more simultaneous mechanics going off. Any mistakes made in dealing with these mechanics can result in a TotalPartyKill. Thankfully, the rewards for winning the fight are well worth it, consisting of high-end armor with five materia slots per piece.
** The Bozjan Southern Front contains three [[DuelBoss Duel Bosses]] ([[MiniMecha Gabriel]], [[TheBeastmaster Beast King Lyon]], and [[PlayingWithFire Sartauvoir the Inferno]]) that can only be fought by finishing an associated Critical Engagement without getting hit and getting selected for the duel in a roulette. Each one requires careful planning of Lost Actions to have any hope of success, and beating all three gives you the achievement title "Sword of the South."
* ''VideoGame/KingdomOfLoathing'' has the final bosses of the Clan Dungeons, and the three final bosses of The Sea.
** Mother Slime in the Slime Tube, who can be up to level 8700. She can also gain immunities to elemental damage and is immune to stunning moves and items.
** The Necbromancer in the Haunted Sorority House, who has three forms and a special attack that takes 30% of your HP.
** Hodgman the Hoboverlord in Hobopolis, who has 25000 HP, gains buffs depending on whether his [[TheDragon dragons]] are defeated or not, and is one of the few enemies that can flip out unprovoked. Defeating him earns you one of many powerful items, but the strongest, his Imaginary Hamster, requires [[SpeedRun getting to him in one day and in under 1100 turns]]. Due to the timing involved, this means not killing any of his lieutenants.
** Dreadsylvania has two possible bosses for each of the three zones: the Dreadsylvania Woods ends with either Falls-From-Sky, a [[EldritchAbomination bugbear made of stars]] that hits with a variety of powerful elemental attacks, or [[PunnyName the Great Wolf]] [[Series/{{Airwolf}} of the Air]], a hard-hitting winged werewolf; the Dreadsylvania Village has either Mayor Ghost, who randomly prevents you from dealing elemental damage, using spells or skills, or using combat items in the next round, or the Zombie Homeowner's Association, which is virtually immune to abilities that don't do extra damage to group monsters; finally, the Dreadsylvania Castle ends with either the Unkillable Skeleton, who scales to your stats, prevents use of combat items, and is only vulnerable to physical damage, or Count Drunkula, who takes drastically less damage unless your character is severely inebriated, and must be defeated in ten rounds. [[http://kol.coldfront.net/thekolwiki/index.php/Advanced_Dreadsylvania_Mechanics#Bosses_and_Superbosses There exist Hard Mode versions of the Dreadsylvania bosses]], which are even ''more'' dangerous but drop even better loot. [[GuideDangIt Good luck finding them without a guide.]]
** [[BonusDungeon The Sea]], meanwhile, has bosses that are even tougher than the Clan Dungeon bosses, matched only by the Hard Mode Dreadsylvania bosses:
*** Shub-Jigguwat, Elder God of Violence, who saps all your MP (and some of your HP) at the start of combat, is immune to stuns, and is virtually immune to elemental damage. He will also retaliate fiercely if you hit him with anything but a basic attack.
*** Yog-Urt, Elder Goddess of Hatred, who sticks you with an effect that lasts about eight rounds, caps all your stats around 30, prevents you from using skills, does massive damage to you each round, ''and'' prevents you from attacking her on pain of death. She's also immune to stuns and won't let you use the same item twice in one combat.
*** [[spoiler:Dad Sea Monkee]], who can only be faced in the first place if you beat both of the first two Sea bosses as ''all six character classes'', combine their special drops into six pieces of equipment, and wear them all. He's immune to being stunned, prevents you from using combat items, and is vulnerable to only one of the six types of damage each turn (including physical and all five elements). The order of those vulnerabilities is [[GuideDangIt only vaguely hinted at in the cryptic, unsettling message you get before facing him.]] On top of all that, you have twelve rounds to defeat him before you lose the fight automatically.
* ''VideoGame/DragonNest'' has several high level maps feature alternative routes with different bosses.
* There are several in ''Videogame/StarWarsTheOldRepublic'':
** Commander Mokan in the Battle of Rishi flashpoint on Hard Mode is a very intense coordination and healing check. He has two types of compounds, compound seventeen and compound nine. The group needs to have a balance of both compounds in order to survive. If the player gets 5 stacks of compound nine, they will die instantly. The boss will deliver lots of stacks of this compound to the tank and the healers can only cleanse one stack unless the tank uses injectors of compound seventeen to reduce the number of stacks. Mokan will release compound seventeen to the group so they need to take compound 9 to reduce the damage. It's no surprise that most groups skip this boss.
** The Dreadful Entity. To summon the Entity at all, Dreadtooth, the world boss of Section X, must be defeated with full stacks of Dreadful Resurgence. The fight is quite a task, almost demanding a full operation's group. To add to it, Dreadtooth only gains stacks as he is defeated. Upon spawning, he starts with two. When he spawns again, he has four and so on. If Dreadtooth is defeated, he drops a special amulet which can be used to summon the Entity during the "Terror From Beyond" operation. But only in 16-player Hard Mode. To add to this, he has a special ability, Dread Touch, which is mitigated by another item: the Dread Guard's Corrupted Mask.
** Upon Dreadful Entity's defeat, the Dreadful Entity drops an item called the Dreadful Orb. This is used to summon the second bonus boss - The Hateful Entity, in the Scum and Villainy operation on 16-player Nightmare Mode. Boasting the same abilities as Dreadful, but hitting much harder and requiring very specific kiting tactics to defeat, the sight of players with his unique title are rare indeed.
* ''VideoGame/RuneScape'' has two types of bosses in its lore: the first are known as quest bosses - one time fights to advance plot; the other are bonus monsters, where killing them is either a fun way of passing the time, or provides high level loot not available anywhere else. Many of them require quests to access, such as the [[{{Undead}} Corporeal Beast]]; while others are just in a dangerous area, such as the [[EldritchAbomination Chaos Elemental]]. The FinalBoss title is granted to anyone strong enough to beat 5000 of these bonus bosses, which includes 100 kills of each kind of boss. The Dominion Tower gives rewards for those who can defeat the quest bosses once more.

*** ''VideoGame/MegaMan10'' features the return of the [[QuirkyMinibossSquad Mega Man Killers]] (Enker, Punk and Ballade) - again as [=DLC=] Time Trial stages, but unlike with Fake Man, Mega Man (and only Mega Man) can permanently get their weapons.

** Both [[VideoGame/RatchetAndClankGoingCommando second]] and [[VideoGame/RatchetAndClankUpYourArsenal third]] game of original trilogy have these in [[MonsterArena Gladiator Arena Challenges]]. The second has four: the first arena includes Chainblade and B2-Brawler - the latter is pretty difficult to beat when you first enter Maktar Resort. The second arena has Arachnoid and Megapede. The third game has only one dual-bonus boss, Terrible Two - the second boss, Scorpio, has to be fought later in the game. These bosses appear as separate challenges, challenges with some kind of limitation ([[NoDamageRun taking no damage]], weapons switching on its own ...) and usually take part in ultimate challenge consisting of many rounds.
* ''VideoGame/DynamiteHeaddy'' has a Bonus Boss called "The Money" that is unlockable with a password you get by beating the bonus game four times.
* ''VideoGame/LaMulana'''s infamous [[BrutalBonusLevel Hell Temple]] has its own guardian, The Boss (no, not [[VideoGame/MetalGearSolid3 that one]]), a giant blob with Naramura's (the game ideator) signature face that [[ShoutOut behaves a lot like the 4th boss of ''Maze Of Galious'']] and summons smaller copies of himself that throw grenades around. Interestingly enough, The Boss is generally easy compared to the level around him.
* ''VideoGame/TheLegendOfSpyro: Dawn of the Dragon'' has Elite Enemies in every chapter. They look like [[PaletteSwap normal enemies with a few modifications.]] [[BossInMookClothing They're not.]] They're hard to ''damage,'' let alone kill...
* ''Franchise/{{Kirby}}'':
** ''VideoGame/KirbySuperStar'' ''[[VideoGameRemake Ultra]]'' began the tradition of including one at the end of the [[BossRush True Arena]]. This game features [[spoiler: [[BackFromTheDead Marx Soul]]]],who is infamous for his [[SensoryAbuse death screech]].
** ''VideoGame/KirbysReturnToDreamLand'':
*** The game has a Bonus Boss that is exclusive to the BossRush mode called "The True Arena". [[spoiler:It's Galacta Knight, the popular FinalBoss of the Meta Knightmare Ultra mode of ''Kirby Super Star Ultra''.]]
*** Also, there's a boss in Extra Mode that doesn't appear in the regular mode. [[spoiler:It's the giant Dedede robot seen in the trailer for the cancelled Gamecube ''Kirby'' title that would eventually be retooled into ''Return to Dream Land'', given a new Metal General-themed coat of paint and named "HR-D3".]]
** ''VideoGame/KirbyTripleDeluxe'', has [[spoiler:Shadow Dedede and [[VideoGame/KirbyAndTheAmazingMirror Dark Meta Knight]]]] at the end of [[spoiler:Dededetour!]], as well as [[spoiler:[[TrueFinalBoss Soul of Sectonia]]]] in the True Arena.
** ''VideoGame/KirbyPlanetRobobot'' has the last bosses of [[spoiler:Meta Knightmare Returns: Dark Matter Clone, Sectonia Clone, and Galacta Knight]]. In addition, The True Arena has [[spoiler:[[TrueFinalBoss Star Dream Soul OS]], which has a fourth phase (similar to [[VideoGame/KirbySuperStar Galactic Nova Nucleus]])]] exclusive to it.
** ''VideoGame/KirbyStarAllies'' features [[spoiler:Morpho Knight]] at the very end of the unlockable Guest Star mode after the main story. [[spoiler:He gains a [[ThatOneBoss much]] [[NintendoHard harder]] EX form in the [[HeelFaceTurn Mage Sisters']] Guest Star run, as well as [[BossRush Soul Melter]] [[HarderThanHard EX]]]].
* ''VideoGame/SonicTheHedgehog2'' contains one only found in an updated re-release on iPhone/Android. It's still Robotnik/Eggman, this time dropping spiked balls which need to be under him when they fire back up in order to get him into range. [[spoiler:To find it, you need to fall down a bottomless pit in Mystic Cave, a pit which in every other version of the game is a very deep spike pit.]]

* In the fangame ''VideoGame/MarioGivesUp'', returning to "Area of Bonuses" after pressing all four switches allows you to reach [[spoiler:the Key Boss]].

* The Archivist in ''[[VideoGame/DeadlyRoomsOfDeath DROD]] RPG: Tendry's Tale''. You get a special ending for beating him, which was meant to require [[TooAwesomeToUse saving up]] the [[OneHitKill Hand Bomb]] to use on him. The developers didn't actually know whether or not it was possible to get stats high enough to defeat him by normal combat (it is).

* ''VideoGame/MarioKartDS'' has Giant Wiggler, the boss of the secret set of Mission Mode levels that is unlocked after earning at least one star in each of the regular missions. Due to its size, it runs incredibly fast, so you have to use the Star at all times to win the race (luckily, all Item Boxes have Stars and nothing else).

* The Smokey Progg in ''VideoGame/{{Pikmin}}'' is one of these, as you have to go out of your way to find it (and do so before the end of Day 15, [[PermanentlyMissableContent or else it'll disappear forever]]) and it drops an object that produces 100 Pikmin when it dies. It has the difficulty to match as well: just touching its slime trail can kill several Pikmin at once, and any Pikmin attacking the Progg will probably be thrown right into it.
** ''Pikmin 3 [[UpdatedRerelease Deluxe]]'' features a new boss at the end of the "Olimar's Comeback" sidestory: [[spoiler: a golden mix between a Shaggy Long Legs and the otherwise-absent Raging Long Legs from ''Pikmin 2''.]] Since it's not part of the main game, it lacks a Piklopedia entry and thus goes unnamed.

* ''VideoGame/{{Smite}}'' has the Fire Giant (and [[Myth/EgyptianMythology Apophis]] for the Clash map).
* ''VideoGame/HeroesOfTheStorm'' has either golem-like mercs or various others, depending on the map.
* ''[[VideoGame/DawnOfWar Dawn of War II]]'' has two optional missions. One, against the Eldar, has you fight an [[PhysicalGod Avatar of their war god]], which is considered to [[ThatOneLevel the hardest mission the the game]], not just because the avatar is really strong, but because the damn thing calls in lots of vehicles for help. The other has you fight an [[AssKickingEqualsAuthority Ork Warboss]], who, while weaker then the Avatar, is still considered tougher than the final boss, though part of that is clearing either of the levels gives you a nice set of Terminator armor and because in the final level, you get to use your entire squad, unlike the rest of the game.

* ''VideoGame/{{Mindustry}}'' has an interesting variation of this trope - ''all'' bosses spawn much later than what you need to do to achieve the victory condition on their respective maps, and in early game you likely won't even encounter them unless you were deliberately aiming for HardModeFiller.

* ''VideoGame/GuitarHero'':
** [[https://www.youtube.com/watch?v=W4M7f4-bhbE This bonus level from Guitar Hero III]], featuring Music/DragonForce's "Through The Fire And Flames", may be harder to beat than any of the above examples.
** There's also its predecessor: "[[https://www.youtube.com/watch?v=H8Xb5XyY5cE Jordan]]" from ''VideoGame/GuitarHero II''. The note chart for this song isn't as horrible, but since Guitar Hero II gives much less time for you to hit each note, the difficulty is comparable.
** ''Satch Boogie'' for Guitar Hero World Tour.
** The spiritual successor "Visions" from ''Rock Band 2'', utterly punishing on both [[https://www.youtube.com/watch?v=DJralxgefcE guitar]] and [[https://www.youtube.com/watch?v=RoHWwrTeYLY drums]].

* VideoGame/{{Bemani}} games in general usually have an unlockable Extra Stage with one or more "boss" songs, which are always among the hardest in the game. Do well enough on that and you'll get to play the TrueFinalBoss, usually named either "One More Extra Stage" or "Encore Extra Stage", and is generally the hardest song in the game (and [[SequelEscalation gets progressively harder with each subsequent installment]]). ''VideoGame/BeatmaniaIIDX'' is known for having elaborate Extra Stage systems where, on your Extra Stage, you enter a special screen where you select one of several different boss songs. Completing all of these songs and fulfilling certain requirements on them (often a grade and special gauge requirement) will allow you to unlock and immediately play the system's FinalBoss. ''beatmania IIDX 20 tricoro'' introduces the "LIMIT BURST" system, which uses crossovers from other Bemani games as bosses.
* In ''VideoGame/BustAGroove 2'', getting "Fever Time" in each level lets you face off against Pander, a [[NonstandardCharacterDesign photorealistic middle-aged bald man wearing nothing but briefs, a single shoe, and body paint vaguely resembling a panda]] whose dance style is inspired by traditional Japanese [[https://en.wikipedia.org/wiki/Butoh Butoh]] and whose stage is a WhiteVoidRoom with screens displaying seemlingly random black-and-white photographs before turning into an AmazingTechnicolorBattlefield. Unlike every other character, he doesn't have one specific set of combos, meaning that his fight will be unique almost every time. Beating Pander as Robo-Z Gold, the game's standard FinalBoss, lets you play as him.

* ''VideoGame/TheBindingOfIsaac'': ''Afterbirth'', the DLC for the remake ''Rebirth'', provides one in the form of [[spoiler:Hush]]. Beating it the first time will end your run, but the fight itself is optional and subsequent fights will allow you to progress to the next floor after you defeat it. Averted in the next expansion, ''Afterbirth+'', where it has to be fought to unlock the TrueFinalBoss, [[spoiler:Delirium]]. The scoring system encourages fighting [[spoiler:Hush]] for getting a high score in daily runs, as it and the BossRush each give out thousands of points on completion.
* ''VideoGame/DarkestDungeon'' has the Shambler, which can normally only be fought be activating a certain foreboding-looking altar with writing on it clearly stating that it's [[SchmuckBait a very bad idea]]. The monster is not only very strong, but fights in an unorthodox way which is sure to surprise the player in the first fight.
* In ''VideoGame/EnterTheGungeon'', if you spend a total of 1000 coins on a certain item and use it to access a hidden floor beneath the Black Powder Mines, you'll end up running into [[spoiler:the Resourceful Rat, who's likely stolen a ton of goods that you left behind]]. This is a long, difficult fight that consists of multiple phases (the High Dragun and [[spoiler:the Lich]] are the only other bosses with this distinction), with the third and final phase [[UnexpectedGameplayChange playing absolutely nothing like the rest of the game]]. If you win, though, you're treated to a stash of items, weapons and pick-ups.
* ''VideoGame/{{Hades}}'': During any run, it's possible to initiate a fight with [[spoiler:Charon]] by [[spoiler:[[ShopliftAndDie "borrowing" obols from his shop]]]]. While he's not very fast, he has a monstrous amount of health, spams a small arena with a constant barrage of attacks, and does the most damage in a single hit of any boss in the game, including the FinalBoss. However, if Zagreus beats him [[spoiler:he'll get to keep the "borrowed" money and will even be given a membership card that cuts 20% off all future shop purchases for that run.]]

* The Gargoyle in ''VideoGame/{{Koudelka}}'', on Disc 3/4. At the same time, it's also ThatOneBoss - because even for a bonus boss, it is just insane. Also, it's a HopelessBossFight on Disc 2 - when the titular heroine fights it alone, she'll deal no damage and will be forced to run away.
* ''VideoGame/SkiesOfArcadia''::
** The original game has some. You don't have to fight any of the giant monsters (Obispo, the Roc, the Giant Looper, and Alania). There's also [[MetalSlime Elcian]], a super Looper who appears in the Dark Rift near the end of the game, who puts up a tough fight but gives good experience and loot and can be fought multiple times, making him great for LevelGrinding. And finally, OneHundredPercentCompletion unlocks one final battle against [[spoiler:Air Pirate Vigoro]].
** The bounty bosses in ''Legends''. They are also ThatOneBoss - because even for a bonus boss, their difficulty is sadistic.
* Ragu o Ragula in all of the ''VideoGame/WildArms'' games for UsefulNotes/PlayStation, [[UsefulNotes/PlayStation2 PS2]], and [[UsefulNotes/PlayStationPortable PSP]]. Angolmois also appears in some of them. In fact, the Wild [=ARMs=] games have many bonus bosses, often found [[SealedEvilinaCan sealed in crystals]] found throughout the game. Ragu o Ragula is neatly incorporated into all of these titles as the sleeping demon who is fated to destroy Filgaia, centuries after the conflict-of-the-day is finished off. Big extra credit for overachieving heroes. The other bonus bosses can range from CallBack characters, characters who are no longer a part of the main plot and have been more-or-less forgotten by the main cast, and [[ItMakesJustAsMuchSenseInContext nudie mags]]
* Gabriel Celesta and the Iseria/Isis/Ethereal Queen in ''VideoGame/ValkyrieProfile'', the ''VideoGame/StarOcean'' series, ''VideoGame/RadiataStories'', and ''VideoGame/InfiniteUndiscovery''. Also, Freya from ''Valkyrie Profile'' is the strongest boss in ''VideoGame/StarOceanTillTheEndOfTime'' where she makes a cameo appearance along with Lenneth.

* The ''Franchise/BaldursGate'' series:
** Aec'Letec in the ''VideoGame/BaldursGateTalesOfTheSwordCoast''. He's more of a FinalBoss to the expansion pack; said expansion pack is an optional sidetrack from the main story, he can be safely skipped after finishing Durlag's Tower and is much worse than the game's actual final boss.
** Kangaxx in ''VideoGame/BaldursGateII'', who could only be hit by +4 weapons, and, in his demilich form, could cast the annoying insta-kill spell Imprisonment at will, which had the tendency to mess up romances if your love interest got hit. Kangaxx does have an AchillesHeel, however, in the form of a [[WeaksauceWeakness shockingly poor]] [[OneHitKill death save]] for his level.
** Most of the dragons in the game are also optional fights, though they give some good rewards after being slain.
** There's also an optional (and completely story-irrelevant) fight against some demon knights in the Underdark.
** In the expansion pack ''VideoGame/BaldursGateIIThroneOfBhaal'', the Bonus Boss was Demogorgon, an incredibly powerful demon imprisoned at [[Main/BonusDungeon the bottom of Watcher's Keep]].
** The Twisted Rune is an order of evil spellcasters who, when you enter their lair, assume that you've come to foil their plans and attack you. They're sensibly skeptical if you claim to have found them by accident, because the only way that would happen is if you were wandering around a bad part of town while carrying an incredibly rare and valuable type of gemstone and opening doors at random. (This is in likely exactly what happened, unless you looked at a guide. The clues that would lead you to them were never put into the game.)
* ''VideoGame/PillarsOfEternity'' has the Master Below: [[spoiler:a giant GreenRocks-laced dragon]] residing at the lowest level of the Endless Paths of Od Nua--itself a {{Marathon|Level}} BrutalBonusLevel. Later patches and expansions added separate encounters with Concelhaut and Llengrath, two of the most powerful mages in the world. Llengrath is accompanied by two dragons, making it one of the most difficult battles in the game.
* ''VideoGame/DragonQuest'':
** Divine Dragon/Divinegon in ''VideoGame/DragonQuestIII'' became available to fight after beating the game. You even needed to beat him five times to gain access to all of his wishes. The Game Boy Color version of this game introduced yet another bonus boss, [=GranDragn=]. Getting to this boss required you to complete such a long, boring, and ridiculous fetch quest that even the most hardcore and dedicated gamers have never seen him.
** ''VideoGame/DragonQuestIV'': The DS remake adds an extra chapter after defeating [[BigBad Psaro]]. Explore a new dungeon, fight Foo Yung and Chow Mein, and you have the opportunity to [[spoiler:revive Rosa, get Psaro joining your party and kick the ''real'' BigBad's butt]].
** ''VideoGame/DragonQuestV'': Not including the later remakes of earlier games, this was the first ''Dragon Quest'' to have one of these, as well as an accompanying Bonus Dungeon. Estark, the original form of the final boss of ''Dragon Quest IV'', is the boss. He would become the recurring Bonus Boss for the series.
** ''VideoGame/DragonQuestVI'' has Nokturnus (better known as Dark Dream), who, thanks to his appearances in the ''Monsters'' series, is considered by many to be ''the'' quintessential Bonus Boss of the series. Nokturnus actually gets a little more plot relevance than the average Bonus Boss, in that during the story, you witness a king try to summon him to deal with the BigBad, only to be violently reminded that EvilIsNotAToy. Though, if you're strong enough to put Nokturnus in his place, he really ''will'' deal with the BigBad on your behalf.
** {{God}} in ''VideoGame/DragonQuestVII''. And the four spirits, which is the odd thing since they are supposed to be weaker storyline wise than both the Last Boss and God, yet you can't fight them unless you can beat God easily.
** The Dragon King in ''VideoGame/DragonQuestVIII''. Have fun with the Darksteel Dragon as well; he's a Metal Slime with a lot better attack, who attacks ''three times'', and, just for more fun, he has nearly 2000 HP.
** Half of the bosses in ''VideoGame/DragonQuestIX''. Of special note are the grotto bosses, [[spoiler:who are revealed to be fragments of the Grand Architect Zenus]], and the legacy bosses, the final bosses and some midbosses from every previous serial title (e.g. Dragonlord, Zoma, Estark, Rhapthorne, etc.) The best kind of PanderingToTheBase. You can even opt to give the legacy bosses the experience you gain from beating them, and they will level up each time, to a max of 99.
** ''VideoGame/DragonQuestXI'':
*** There are beefed up versions of the Spectral Sentinels as the bonus bosses of Act 3's BonusDungeon.
*** The Definite Edition and 3DS version has the End of Time, a golden palette swap of the TrueFinalBoss [[spoiler:Calasmos]], who is much tougher than the final boss in question. Exclusive to the Definitive Edition is also the Timewyrm, another golden palette swap, this time of Act 2's final boss [[spoiler:Mordegon]] who is tougher than even the End of Time and takes the cake as the hardest boss in the game.

* ''VideoGame/PaperMario'':
** Bloopers who shows up every time you find a new shortcut in the sewer (though the last one is mandatory). Kent C. Koopa also blocks a road and makes you pay to pass; beating him lets you pass for free. Then there is a Dojo, where you can fight for bragging rights. The final blooper, Kent C., and the Dojo Master could all give Bowser a run for his money if he didn't have the Star Rod.
** There's also the [[BossInMooksClothing Anti Guy]], found guarding a chest in a dungeon halfway through the game and with HP and attack roughly on par with Bowser's penultimate form. He can be beaten straight-up, or you can exploit his SweetTooth to bribe your way to the chest's contents.
** In Chapter 8, if you flunk a quiz from one of the Bowser-faced stone doors, your punishment will be a NoHoldsBarredBeatdown against ''three'' Anti Guys. Easily the most difficult fight in the game, as Mario will initially be taking in the ballpark of 25-30 damage a turn with (unlike all the above bosses) no way to cheese your way out of it.
* ''VideoGame/PaperMarioTheThousandYearDoor'':
** Bonetail gives the game's final boss a run for its money (which is lampshaded by [[MetaGuy Goombella]]) and requires going through a dungeon with 90 consecutive battles (99 floors with a "breather" every 10) to reach him. He is a bit easier than the final boss, as you'll probably be better equipped and levelled by the time you reach him, and his attacks aren't as complex to deal with - he just has enormous attack power and endurance, and getting to him is a massive two hour-long ordeal.
** Atomic Boo, fought in Creepy Steeple if you enter the main hall and take the Spin Hammer attack to the swarms of Boos enough times. He isn't particularly hard, but knowing he even exists is a bit of a GuideDangIt.

* ''VideoGame/DarkSouls'' is absolutely swarming with these guys; due to the open-ended nature of the series, it's very possible to skip a large cut of the bosses in the game just to only finish the mandatory bosses to "win" the game. [[HarderThanHard And you should be very thankful for that, a lot of the time]]. To wit:
** [[NamesToRunAwayFrom The Hellkite Dragon]] that guards the bridge between the Undead Burg and Undead Parish is more of an obstacle than an actual boss, but players have naturally decided to try to kill him regardless. If you do decide to try to kill him, you have to continually dodge that 1 hit kill fire breath of his and bait him to land on the bridge to actually deal damage. Forget ranged attacks: at lower than 50% health, he starts ''regenerating'' at a rate that will almost certainly outpace your ranged attacks, and is tough to overcome even with melee. However, you don't even get anything other than 10,000 souls for killing him, which, at the level you're likely to be at if you do kill him, isn't all that much. So killing this dragon really just ends up being for bragging rights.
** The game has several in the optional areas of the game. The first one most players see is the Stray Demon, a much stronger version of the tutorial's Asylum Demon that drops a highly valuable Titanite Slab. Others include the magical Moonlight Butterfly in Darkroot Garden, the illusionist Dark Sun Gwyndolin in his father's tomb, and the half-Dragon Priscilla in [[BonusLevel the Painted World.]] Priscilla is a little bit more optional tham usual because she won't attack until the player does first, and her dislogue points out that you can exit the boss arena and pass through the Painted World without a fight. The difficulty of these encounters depends on the player's progress through the game and they are much easier than the final boss, but they still provide a unique challenge to those who look for them.
** The DownloadableContent ''Artorias of the Abyss'' adds a new hidden BonusLevel with several bosses in it, all of them difficult fights. The bonus content even has its own bonus boss; while most of the bosses block off new bonfires and are normally accessible, the black dragon Kalameet is unlocked by a side quest and only gives the [[BraggingRightsReward Calamity Ring as a reward, which double all damage taken.]] Cutting off his tail creates a powerful weapon, but doing that is even harder than killing him. Adventurous players can also find a fight against two of the first [=DLC=] bonus boss at the same time.
* ''Videogame/DarkSoulsII'' has several:
** The Ancient Dragon is a brutal MarathonBoss with a lot of health and all of its attacks can kill you in one hit unless you have extremely high Fire resistance. The saving grace is that most of its attacks are fairly telegraphed and can thus be avoided rather easily. Except when it decides to fly up and rain fire on the arena. Avoiding that can be a struggle. Upon defeat, it drops an item that makes the next Bonus Boss easier.
** [[spoiler:King Vendrick]] is an AnticlimaxBoss whose attacks are slow and easy to dodge, though he can kill you in one hit if you aren't careful. However, he is also a PuzzleBoss since his defense is incredibly high, making him impossible to defeat if you don't have [[spoiler:Giant Souls]] in your inventory. Upon defeat he drops nothing. [[spoiler:The rewards appear behind a hidden locked door in a different area.]]
** The Darklurker is the most obscure. The previous two are at least encountered in the storyline. It is entirely possible to never encounter this boss [[GuideDangIt if you aren't playing with a guide]]. You need to discover and join an hidden covenant and fight through three small dungeons filled with dangerous black phantoms just to meet the Darklurker. Your efforts are "rewarded" with a harrowing battle against an eerie angelic figure who hurls powerful pyromancies, hexes, and sorceries at you while flying around the arena. It [[SquishyWizard thankfully has much lower health]] than the other two bonus bosses. Upon defeat, it drops its soul which can be traded for a powerful hex. Its defeat also maxes out devotion to the hidden covenant, which comes with its own rewards.
** Also notable are the DLC challenge areas, four NintendoHard optional paths designed for co-op. All of them have appropriate bosses at the end, though all except [[spoiler: Sir Alonne in the Memory of the Old Iron King]] are Invader type enemies or palette swaps.
** You need four [[PlotCoupons Great Souls]] to reach Drangleic Castle, and there are four bosses with Great Souls. However, you can kill one boss, take their Great Soul, use a Bonfire Ascetic to resurrect that boss, then kill them again and take a whole new Great Soul again. Repeat ad nauseum and almost every boss in the game before Drangleic Castle is Bonus.
** Raime the Fume Knight from the ''Crown of the Old Iron King'' DLC is one of the toughest bosses within the entire game. It's telling when you find messages outside his fog wall commenting on misery and sadness ahead, because he's statistically the boss with the highest failure rate in the game. Most of his attacks come in hard and fast with his straight sword, but then occasionally he'll swing his ultra greatsword and either shave off a massive chunk of your life or utterly ruin your stamina. After he's lost about a third of his HP, [[TurnsRed he gets serious]], buffs his ultra greatsword with a dark flame and gains a new, significantly more aggressive move-set that punishes players that either can't time their dodge right or just stand there expecting to block his strikes. Additionally, if you haven't collected the Smelter Wedges throughout the DLC, Nadalia's idols will keep healing him if he's near them, and if you have Veldstadt's helm equipped, Raime will immediately enter his second phase move-set without you hitting the HP threshold.
* ''VideoGame/DarkSoulsIII'' ups the ante with the Nameless King, who is considered one of the toughest direct fights in the entire series. First you fight him on his Storm Drake, the King of Storms, who is so large that [[CameraScrew locking onto him makes it near impossible to see the Nameless King's attacks from above,]] combined with a particularly difficult to avoid fire attack from above you can only evade if you start running the ''instant'' the Drake starts flying overhead. Once the Nameless King is on-foot, however, it only gets [[UpToEleven harder;]] put the moveset of Ornstein with a super adrenaline boost on a [[PhysicalGod God of War]] that is hyper-aggressive, extremely mobile, and can kill even the sturdiest of builds in a handful of blows, and pair this with fighting on a moving cloud background that hinders depth perception. It's not uncommon to see 85% of the fight, at minimum, being spent ''rolling for dear life.''
** It's also possible to beat the game without even realising that you can cut the rope bridge in the Catacombs of Carthus to turn it into a ladder to Smouldering Lake, so you end up missing the MiniBoss battles against the Fire Demon and Carthus Sandworm, plus the battle against the Old Demon King.
** None of the DLC has to be completed to win the game, meaning that [[spoiler:Sister Friede]], Halflight, Spear of the Church, the Demon in Pain and Demon from Below, and [[spoiler:Slave Knight Gael]] are somewhat optional, but you can finish the main story of ''Ashes of Ariandel'' without finding out that the area the Champion's Gravetender and Gravetender's Greatwolf fight is in even exists, let alone getting to it, and Midir's boss arena in ''The Ringed City'' requires you to defeat him on a bridge and then figure out where the hell his proper arena is.
* ''VideoGame/{{Bloodborne}}'', naturally being a SpiritualSuccessor of ''Dark Souls'' as listed above, has even ''more'' optional boss encounters than ''Dark Souls'' does, owing to the fact you're actively hunting out these horrors than reacting to their mandatory discovery like in ''Dark Souls'' - and make no mistake, these include more than a few nasty surprises lurking within the depths of Yharnam that don't have to be beaten in order to win the game, but doing so anyways nets new content, areas and locations:
** The Cleric Beast is a boss that doesn't have to be fought in order to win the game, yet he's very commonly the first boss many players fight by virtue of gating off exploring more of Yharnam, and he [[EstablishingSeriesMoment establishes the de facto nature of the game]] by being ''very'' aggressive unlike almost any other boss in ''Dark Souls'', and actively punishing tactics of turtling by forcing you to be constantly on the offensive while dodging each of the Cleric Beast's attacks. For many players, it serves as a WarmUpBoss and in many ways equivalent to ''VideoGame/DarkSouls3'''s own Iudex Gundyr for being the "tutorial" boss.
** The Blood-Starved Beast is encountered in the dead-end segment of the Church of the Good Chalice, and he is ''ridiculously'' aggressive and hard-damaging, while also boasting poison damage and rapid-fire attacks that'll leave most players dead before they can even react. The way in order to quickly defeat this boss is to either be even more aggressive than it while reading its tells, or simply [[spoiler:[[OutsideTheBoxTactic using Pungent Blood Cocktails]] to lure the Beast away from you and to the location where you tossed it]]. Given how aggressive the boss is, you'll likely need every advantage you can get.
** The Old Hunters DLC adds four new super-bosses to the game, all of which are varying assortments of pure ''nasty''. How nasty, you may ask? Nasty enough that for every single boss according to [=PlayStation=] 4 Trophy data, ''[[HarderThanHard less than 40% of every single boss in the game was actually completed against]]'', with the vast majority being fights that most people just gave up against or skipped entirely. To name them in order of appearance assuming HundredPercentCompletion:
*** The first mandatory encounter is Ludwig, the Accursed, [[WasOnceAMan who was once a proud hunter that sadly became a horrific horse-like monstrosity]]. The fight immediately has the DLC go for the jugular with highly-damaging and outright ''aggressive'' attacks that'll very likely two-shot if not ''[[OneHitKill one-shot]]'' you, and being very hard to get a read in on without being punished by the absolutely frantic pace of the fight comes at. Even worse, just when you think the second phase is going to be merely a more aggrssive version of the first fight, [[spoiler:Ludwig regains his sanity and becomes Ludwig, [[RedBaron the Holy Sword]], and promptly equips itself with From Software's trademark [[RecurringElement Moonlight Greatsword]], which changes the fight from a fight against a crazed beast to the dignified slashes of a MasterSwordsman, and the fight as a whole ''will'' wreck your face in if you don't change tempo immediately]].
*** The next boss is Laurence, the First Vicar, which is basically the unholy fusion of the Cleric Beast and Vicar Amelia on steroids, and also ''[[ManOnFire on fire]].'' He immediately gets ridiculously aggressive and very hard to dodge with a frenetic and frantic combat pace throughout the entire fight that ''will'' smash your face in if you don't come with lots of preparation, whom even then will probably kick your ass. This is because on top of a wild first phase, the second phase has Laurence [[TurnsRed Turn Red]] and lose his legs, which makes him even ''more'' dangerous as he begins spewing fire everywhere and potentially one-shotting you while he rampages around the place. It really ought to be telling that in a DLC that's already optional to beat the game over and serves to test your challenge, Laurence is the only boss in the entire DLC who ''isn't'' mandatory to fight, giving it a double dosage in being a royal pain in the ass that is only to be beaten for a BraggingRightsReward.
*** The second mandatory boss in the DLC is Lady Maria of the Astral Clocktower, who is unique in being one of the only purely-human bossfights in the game, aside from [[spoiler:Gehrman, the First Hunter]] and [[OurWerewolvesAreDifferent technically]] Gascoigne, and yet ''still'' manages to be ridiculously hard. On top of [[FlashStep Flash Stepping]] everywhere to the point of teleport spam, she is also ludicrously fast and will likely cut your Hunter to ribbons before they could even react. The second phase of the fight is even worse, as she ends up ''slashing herself to use a blood blade that is set on'' '''''fire''''', and she uses it in reckless abandon in a last-ditch attempt to stop you. What makes this even more interesting is that the lore of the fight reveals [[spoiler:Maria always hated blood weapons, something confirmed by the description of the Rakuyo; given [[TheseAreThingsManWasNotMeantToKnow what she's guarding]] and her involvement in the atrocities that occured in the Fishing Village, it's very understandable that [[BatmanGrabsAGun she resorts to using the very things she hates]], [[GodzillaThreshold just to stop you from reaching the Fishing Village]]]].
*** The FinalBoss of the DLC and arguably the TrueFinalBoss of the entire game is regarded by many players as one of the hardest bossfights, if not '''''the''''' hardest bossfight, [=FromSoft=] has ever put out in [[VideoGame/DemonsSouls any]] [[VideoGame/DarkSouls of]] [[VideoGame/{{Bloodborne}} its]] SoulsLikeRPG games. How hard, you may ask? Hard enough to put every single boss in the ''entire game'' and on this list (and hell, most bosses on ''this very page'') to ''shame.'' It is none other than the [[spoiler:Orphan of Kos, the child of the deceased Great One Kos]], whom promptly proceeds to prove to be ''vicious.'' It is ''extremely'' aggressive beyond what should be possible for an already-aggressive game like ''Bloodborne'', extremely hard to read tells to dodge its attacks, and is both [[LightningBruiser faster, stronger and more durable than you will ever be]]. Combine that with the bossfight being in many ways a MirrorBoss with [[spoiler:the Orphan using its, ahem, [[DoesThisRemindYouOfAnything placenta-like organ]]]] as a Trick Weapon as they ''very'' quickly began swarming against you with an absolute slew of aggressive attacks that get even ''worse'' on the second phase; it's aggressive enough that ''[[ReadingsAreOffTheScale even in a game with aggressive combat in mind]]'', it's the ''one'' boss that is completely impossible to control through aggression alone, resulting in many, ''many'' player deaths just to kill this thing, with a non-insignificant number of these players giving up outright. Given the fact that [[spoiler:the Orphan of Kos is merely a ''baby'' Great One, and is even more dangerous than any other Great One boss in the entire game by a mile, is it any wonder why the Hunters were so desperate to keep it contained to the Fishing Village?]]
** Among the optional Chalice Dungeons is also a massive amount of optional bosses, from the Amygdala, to the Bloodletting Beast, to the Maneater Boar, to the Watchdog of the Old Lords, all of which are more than capable of ruining the day of any traverser of these underground, optional randomly-generated dungeon treks. Special mention explicitly goes to the Watchdog of the Old Lords, as they're both on fire like Laurence is, ''and'' is most likely fought in a dungeon that cuts your total HP count in '''half''', with most of its attacks very often being one-hit kills given the level you're required to fight it at, making for an infuriatingly difficult boss trek.

* ''VideoGame/{{Atelier}}'':
** The 3 Golden Pigs at the end of the BonusDungeon (Mull's Dungeon) in ''VideoGame/AtelierIrisEternalMana'', which are significantly more difficult than the final boss.
** In ''VideoGame/{{Atelier Iris 2|The Azoth of Destiny}}'', the fights at the Dragon's Nest, particularly the last one against 3 Instant Brownies. However, while they are more powerful than the last boss, the overly-easy battle system makes them no more difficult than anything else, provided the player has stocked up on resurrection items.
* Kisuke in ''Manga/{{Bleach}}: Soul Carnival 2.'' The thing with him, though, is that he can be fought pretty early on in the game, not that you'd have any chance of survival then. Until you clear the Soul Society missions, he'll probably kill you with just one combo. And he has two supports, whereas most bosses only have one, '''OR''' the fact that his Burning Attack can even hit you if you're off-screen, and it stuns you invariably (as Burning Attacks never miss). When you defeat him, you'll unlock him as a playable character.
* ''VideoGame/BreathOfFireIII'' had the Berserker, difficult because it attacked for three to four hundred damage, and often attacked several times before any of your characters got to. Worse, it was a [[BossInMookClothing random encounter]] on the way to getting one of your dragon genes, and was a normal monster.
** And in the same area was an even tougher Bonus Boss, the Arch Mage. He has far less HP than Berserker (only about 3,000 compared to the Berserker's 15,000), but regenerates 1,500 of it every single round, which is more than most casual players can deal in a single round, and is capable of hitting just has hard as Berserker. In fact, if you have one living and two dead characters, Arch Mage will USE A SKILL THAT REVIVES THE TWO CHARACTERS. Presumably, he does this simply as a means of embarrassing you further.
* ''VideoGame/BreathOfFireIV'' has Rider as a hellish random encounter in Mukto. With 40,000 HP he is already a tough opponent but he also regenerates 20,000 HP every turn...try to overcome that.
* ''VideoGame/BreathOfFireDragonQuarter'' had Dover, who was the final boss in the BonusDungeon. As long as you have a high enough level (around 50), he's not that bad. The only problem is is that his defense switches from regular ol' attacks to Dragon defense. So your time limit is based on how much you have left on the D-Counter. [[SpellMyNameWithAnS Lin's/Rin's]] "Shatter!" technique is particularly effective here.

* The ''VideoGame/EtrianOdyssey'' series as a whole has a '''''LOT''''' of bonus bosses; many of them are usually part of {{Side Quest}}s, and about half of them are post-end game only.
** Prevalent in all games except the fifth are the post-game [[FireIceLightning three elemental dragons]] (Great Dragon, Blizzard King and Storm Emperor), who each has an elemental attack that can wipe out your entire party in one hit unless you negate it with specific skill at the right time. From the third game onwards, their defeat also raises the level cap for your entire guild -- an important asset for the postgame.
** Even before end game, there're usually a few bosses that can be fought early on, but definitely not recommended as they are usually far too powerful that early. The Wyvern and Salamander from the first two games are good examples.
** The third game, ''The Drowned City'', introduced a second exploration map (the sea), thus ramping up the number of bonus bosses in the game. Same deal with the fourth game, ''Legend of the Titan'', and its skyship map.
** Finally, to top it off, each game has a BonusDungeon that houses the TrueFinalBoss of the game, and it goes without saying that they are excruciatingly difficult, sometimes requiring strategy guides that lists what they will do ''turn by turn'' just for you to have a chance to beat them.
** In absence of the elemental dragons, ''Beyond the Myth'' has an all-new catalogue of Bonus Bosses: Dryad in Tutelary Forest, the Primordiphant in Jagged Reach, the Zombie Dragon in Fetid Necropolis, Lamia in Lucent Hollows, and [[spoiler:Star Devourer (the one who killed Arken's race)]] in the BonusDungeon. The Primordiphant is the only one that makes an appearance during the main story, and the objective at that point is to figure out how to ''avoid fighting it'' (the sidequest tasking you to face it will only pop up after the main story is completed); all others will start appearing one by one in the postgame.
* In ''Anime/DragonBallZ: Super Saiya Densetsu'', if Goku becomes a [[SuperMode Super Saiyan]] during the final battle with Frieza (accomplished by allowing a party member like Krillin or Chiaotzu to die) and he and Vegeta survive to the end of the battle, after the credits you'll get a scene of Vegeta going Super Saiyan and challenging Goku as payback for the humiliation he suffered back on Earth.

* ''VideoGame/BahamutLagoon'' has special "side quests" - essentially single battles - available throughout the game. One of them, appropriately named Hard Dungeon, is only available in the last seven chapters and is far more difficult than the final boss.

* After beating Machinedramon and finishing the main story in ''VideoGame/DigimonWorld'', you can continue the story and find a new level with high powered {{Mook}} Digimon. At the end is Machinedramon once again, only this time his health is maxed out at 9999 and his stats are also quite high. This is all for bragging rights.

* The UsefulNotes/Xbox360 game ''VideoGame/BlueDragon'' has several Dragons that don't ''need'' to be beaten, but give the player a useful accessory if they are. Genuine Bonus Bosses include the Gold Mecha Robo, the King Poo, and the Golden Poo.
* ''Franchise/DragonAge'':
** ''VideoGame/DragonAgeOrigins'' has several optional bosses among its many sidequests. The Revenants are powerful undead warriors that are managable on their own but get downright nasty with backup such as the ones that drop the Juggernaut equipment. Gaxkang the Unbound is an homage to Kangaxx from ''VideoGame/BaldursGate''. [[spoiler:Flemeth]] shapeshifts into a High Dragon. An actual High Dragon (who ''could'' be beaten easily if you surrounded it with [[UselessUsefulSkill Traps]] before you aggro). And many more.
** ''VideoGame/DragonAgeOriginsAwakening'' gives us the Queen of Blackmarsh, a [[NinjaPirateZombieRobot lightning-breathing spectral dragon]] who is quite unambiguously even more powerful than the FinalBoss. Also, the ''[[BrutalBonusLevel Golems of Amgarrak]]'' {{DLC}} has the Harvester, widely regarded as the toughest boss in the entire ''Origins'' saga.
** ''VideoGame/DragonAgeII'' helpfully marks its bonus bosses with dedicated Achievements you get for offing them: a Varterral, a High Dragon, Xebenkeck the Desire Demon (who happens to be an old chum of Gaxkang from part one), and Hybris the Pride Demon. The last one is [[ThatOneBoss particularly bad news]].
** ''VideoGame/DragonAgeInquisition'' has no less than ''ten'' different High Dragons lurking in various areas, as well as the Desire Demon Imshael (also related to Xebenkeck and Gaxkang). Additionally, there is a ''secret'' High Dragon bonus boss, the [[spoiler:Guardian of Mythal]], whom you can only fight after very specific plot decisions, namely [[spoiler:if Morrigan never gave birth to a child with the Archdemon's soul ''and'' did not drink from the Well of Sorrows]].

* ''VideoGame/{{Dubloon}}'' features [[MusicalAssassin The Quartet of the Seas]], a group of four bosses each found in one corner of the ocean. Alone, they aren't dangerous, but just wait until you fight them all four at once in [[BigBoosHaunt the Pirate's Graveyard]]. They ''will'' kick your ass.

* ''VideoGame/{{Fallout}}'' has had several of these across all the games in the series.
** ''VideoGame/Fallout3'' has five or six [[AttackOfThe50FootWhatever super mutant behemoths]] who you can hunt down. Admittedly, one is a MiniBoss over the course of the main story, but even then, you could just skip the entire section. Other optional bosses include Commander Jabsco of Talon Company, Lag-Bolt and Enclave Squad Sigma in ''Broken Steel'', and the three Ant Queens.
** ''VideoGame/FalloutNewVegas'' has the BigBad himself, Caesar. Especially compared to his second-in-command, Legate Lanius, Caesar is pretty weak for a boss, only being about as tough as an EliteMook. However, he's in the middle of the Legion's stronghold, and his personal section (the only one you're allowed to visit) is crawling with dozens of Legion troops. When you get past them, he is protected by eight {{Praetorian Guard}}s armed with [[PowerFist shotgun fists]], each of which is as powerful as him. At lower levels, Caesar and his guards will usually dogpile you into a corner and beat you to death in a few hits, since said shotgun fists do ridiculous damage and Caesar and his guards are ''fast''. However, if you go there at a later level with a good companion and high level weapons they'll go down easily enough.
** The four (five with ''Old World Blues'') legendary creatures in ''New Vegas'', which are [[UndergroundMonkey reskinned]], [[GiantMook upsized]], and [[ThatOneBoss overpowered]] versions of their normal species. Admittedly, a sufficiently leveled character can make short work of most ([[spoiler:Legendary Cazador, Legendary Nightstalker, and Legendary Fire Gecko]]) but the [[spoiler:Legendary Deathclaw]] from the main game, and [[spoiler:[[LethalJokeCharacter Legendary]] ''[[TheGoomba Bloatfly]]'']] from ''Old World Blues'' can usually kill you in... Two hits. Almost always.
** There's another boss Deathclaw in ''Lonesome Road'', named Rawr. It's a LightningBruiser, even compared to the Alpha Male, and will kill most characters in one hit; it has somehwhat less HP than the Legendary Deathclaw. Defeating him allows you to build one of the most powerful Unarmed weapons from his talons, Fist of Rawr. [[spoiler: Or [[Manga/FistOfTheNorthStar Fist of the North Rawr]] if you have [[SillinessSwitch Wild Wasteland!]]]] There's also Gaius Magnus and Colonel Royez, who are only available [[spoiler:if you choose to nuke the Legion or NCR respectively at the end.]] Both have all of their SPECIAL stats maxed out, and Royez has the third highest HP of any human enemy after Ulysses and Legate Lanius, a Damage Threshold of 24, wields a plasma caster with overcharge ammo, and regenerates his HP very quickly from the radiation.
** ''VideoGame/Fallout4'':
*** Swan, a special Super Mutant Behemoth, resides in the Boston Common's duck pond and wields a gigantic hammer fashioned from an anchor. Defeating him nets you the armor-piercing Furious PowerFist.
*** The optional Quincy Ruins is home to three Gunner leaders, who are backed up by many high-level mooks from the overpasses and other high ground. Two of the bosses wear PowerArmor, and the one that doesn't, Sgt. Baker, is armed with a OneHitKill Fat Man. Clint wields an Engraging Laser Rifle named Good Intentions, and Tessa wears a unique Raider Power Armor Right Arm named Tessa's Fist (not a PowerFist, [[NonindicativeName despite the name]]). Other Gunner bosses include Captain Wes in the Gunner Plaza, and Captain Bridget at Hub City Auto Wreckers.
*** The Far Harbor DLC has a randomly-encountered legendary Fog Crawler named Shipbreaker. Given that normal Fog Crawlers are already [[BossInMookClothing Bosses in Mook Clothing]], this one's insanely difficult to take down, especially because, being a Legendary, it TurnsRed and auto-heals when its HP is depleted halfway the first time. Reporting its defeat to Longfellow earns you the Skipper's Last Stand harpoon gun, which grants +150 damage resistance when reloading.
* ''VideoGame/BatenKaitos Origins'' gives us a few. There's [[spoiler:Nasca, Valara, Heughes, and Wiseman]], who are fought to tie up loose ends; one of them allows access to the game's TrueFinalBoss. There's also Arma Prototype M, a.k.a. The Wicked Gawd, who is the final boss of the Coliseum and is ''absurdly'' hard.
* In ''VideoGame/AlphaProtocol'', the BloodKnight ActionGirl SIE will offer to team up with you during the mission where you first encounter her. You can agree to the alliance, or you can attack her (or you can agree, complete the mission, then attack her when you encounter her again at the end of the mission). Not only will she not die when you win, but [[RelationshipValues your rep with her]] will increase.

* ''Franchise/TheElderScrolls'':
** ''[[VideoGame/TheElderScrollsIIIMorrowind Morrowind]]'':
*** Due to the game's AnyoneCanDie nature, naturally, anyone in the game can be fought and killed. But special mention has to go to [[spoiler: [[PhysicalGod Vivec]]]]. You are by no means required to fight him, and doing so before completing the main quest will make the normal method of beating the game impossible, but if you choose to do so, you'll have quite the fight on your hands. Bonus irony points if you soul trap him in Azura's Star. This is actually recommended, since he has the second most powerful soul for enchanting in the game, after only [[spoiler: Almalexia]].
*** The Ash Vampires. You are only required to fight one in order to get an item (Sunder) off of him, but there are 6 others you can hunt down and kill. Killing them is supposed to weaken Dagoth Ur in the final confrontation, but due to a scripting glitch, this does not happen (and if it ''did'' happen killing all of them would break the game, as Dagoth Ur ''would be dead before you arrive'' leaving you unable to get the result that's supposed to happen when you kill him). Still, they each possess unique enchanted items that are [[PermanentlyMissableContent unobtainable]] if you don't fight them, and you should kill them if you're going for OneHundredPercentCompletion.
** ''[[VideoGame/TheElderScrollsIVOblivion Oblivion]]'' also has a few.
*** Erandur-Vangaril (a lich). He can only be found in a specific cave that none of the game's quests lead you to, and can only be fought there once your character reaches a certain level.
*** The giant slaughterfish, who shows up in one of the dungeons you explore in the Thieves Guild questline, but chances are you won't ever see this one if you don't fully explore the place.
*** There's also the Uderfrykte Matron at Dive Rock.
** ''[[VideoGame/TheElderScrollsVSkyrim Skyrim]]'' has some as well.
*** The Ebony Warrior of the Dragonborn DLC challenges the player once they reach level 80 in the hope that he's finally met someone tough enough to [[NothingLeftToDoButDie kill him]]. His equipment is heavily enchanted, has 50% damage resistance to all elements, is immune to several spells and Shouts, and can use Dragon Shouts in addition to healing spells and potions. There are also a few named dragons which are not required to be fought. Of particular note is [[spoiler: Vulthoryol, who can be summoned by using the Unrelenting Force shout on the orange globe in Blackreach.]]
*** Also in Dragonborn, the player has the option to fight the ghost of [[LegacyBossBattle Kaarstag]], a Frost Giant that was killed by the [[PlayerCharacter Nerevarine]] in Morrowind's Bloodmoon DLC. The player must find his skull and place it on his throne if they wish to challenge him, and after defeating him they gain the ability to summon him in battle three times only.
*** The Dawnguard DLC adds the Reaper, a ghostly headsman that can be fought in the Soul Cairn after finding three gem fragments.

* ''VideoGame/TheDenpaMen'':
** The first game has two. One mid-game dungeon appears to have two bosses--a Water-type Golem and an Ice-type Golem. The Ice-type Golem is [[PathOfMostResistance more difficult to get to, and is the true boss of the dungeon.]] The Water-type Golem, however, gives you a few extra goodies if you beat it. At the very end of the game, you can also choose to fight [[spoiler: The True King, the final form of the King of Evil. He has his own RareRandomDrop, and each time you defeat him, he drops an emblem that can be sold for a [[VendorTrash tidy sum of money]].]]
** The sequel has ''even more'' of these, most of whom are based around chess pieces. Each of the four [[BonusDungeon Caves of Darkness]] contains a different variation on the Knight, and each one is progressively more difficult--especially because the Caves are [[TimedMission timed,]] and even though you can keep battling if you run out of time, if you do, you'll be kicked out of the dungeon before you can collect your rewards for completing it. There's also a Pawn who you have one required fight against early on--but he keeps getting stronger and stronger throughout the game, and you can return to challenge him after different story events. [[spoiler: The last two sets are linked--the "big" BonusDungeon ends with a fight against the Demon Queen, who serves as a combination of this and a TrueFinalBoss. ''This'' unlocks the Bishop, King, and Queen, who fight you back to back in a CallBack to the original game's final boss.]]

* ''VideoGame/EpicBattleFantasy''
** The third game has a bonus room in [[LethalLavaLand Volcano Peak]] that can only be unlocked by collecting all 60 in-game medals. This room has three of these, including a pair of level 50 bushes (in a game where level 30 is the default cap on a first playthrough), a pair of evil worms and their tails (mooks normally only summoned by the FinalBoss), and a trio of one of each type of [[BossInMookClothing monolith]] enemy, all at level 40!
** The Steam release of the fourth game has a whole area dedicated to these, featuring upgraded versions of the main game bosses (except the final boss), the notorious Cosmic Monolith from the third game, and even [[spoiler:evil versions of your party members]]. [[LegacyBossBattle Some of the bosses from the second and third games]] also return in the main game as optional minibosses. The main game also includes the Glitch, a PuzzleBoss based on using NonElemental skills and preventing OneHitKill attacks.
** All versions of the fifth game have the return of the Glitch boss after completing four "glitched" areas and an ''VideoGame/{{Undertale}}''-styled cat boss known as Snowflake after gathering three gems hidden in chambers underground. The first Steam version added harder versions of the four main non-FinalBoss[=es=] (and the Hydra minibosses) in their own mini-dungeons, and beating them grants access to [[spoiler:''alternate'' evil versions of the party members that are more distinct from the Dark Players of the fourth game]]. Version 2 added even more: a BossBonanza of four sketches in the expanded Greenwood Library, twelve hidden 8-bit Arcade minibosses with some sort of central gimmick scattered around the world, [[NostalgiaLevel and eight bosses from the previous games (two from each game) in a series of bunker simulations.]] All of them scale to the players, based on things like level, medals obtained, and how many ''other'' optional bosses and challenges have been completed.
* ''VideoGame/BarkleyShutUpAndJamGaiden'' has a few:
** The spirit of Dikembe Mutombo is the boss of a bonus dungeon and gives Barkley the Holy Dunk attack.
** A duergar [[spoiler:(actually Balthios, who is a Wereduergar)]] can be fought if you take the ferry to Liberty Island instead of the Underground Railroad.
** The Ghastly Darklord is encountered by checking a seemingly empty corner in Proto Neo New York.
** Kevin Garnett is the final opponent in the Arena in the optional [[AnotherDimension B-Ball Dimension]].

* The ''VideoGame/EarthBound'' [[GameMod ROM Hack]] VideoGame/EquestriaBound has a few, who always drop the parties {{Infinity Plus One Sword}}s. According to the hack creator, this was to prevent [[RareRandomDrop Sword of Kings]] situations.

* ''Byteria Saga: Heroine Iysayana'' has a BonusDungeon you cannot enter until you have finished the main quest, with three bosses inside: [[spoiler:Rematches with Vile and Caryneth, and ultimately Lord Sick, one of the archvillains from ''Byteria Heroes''. That series got a ContinuityReboot around the time ''Heroine Iysayana'' was finished and didn't become available in English at all until later, making it something of an EarlyBirdCameo.]]

* A staple of Zeboyd Games: the Dragonduck in ''VideoGame/BreathOfDeathVII'', DEM, SARA and Soulcaster in ''VideoGame/CthulhuSavesTheWorld'', and DEM, Lita, Cthulhu and T in ''VideoGame/CosmicStarHeroine''.

* ''VideoGame/BoxxyQuestTheGatheringStorm'' has at least eighteen of them, and possibly as many as ''twenty-five'', depending on whether you consider the Sky Abyss bosses to be ‘bonus’ or not.
** Pale Luna, the [[VoluntaryShapeshifting Phisher King]], the [[CreepyDoll Fetish Dolls]], Trahald Prime, the [[ChestMonster Hateful Reliquary]], and the Soul of [=TORment=] - all related to the Deep Web BonusDungeon.
** ORDERHEAD, Goddess-Slayer Forby, the Hydra, and the [[{{Santabomination}} Spirit of CTH’RISTMAS]] - appear at the end of various minor sidequests.
** Lady Ny’agai and the [[DanceBattler Funky Infoshade]] - just kind of standing around at the end of side paths, waiting for you to find them.
** [[GlitchEntity not_intended/Nihilerror]] and [[spoiler:Esoteraphim]] - deeply hidden with GuideDangIt requirements, and two of the most challenging fights in the game.
** The three entities labelled “?,” all related to [[BigBoosHaunt /x/]] in some way.
** The Overtaken Dragon, which is encountered along the main path in the final dungeon, but can be skipped by simply [[TreacherousCheckpoint not interacting with a certain save point]].
** The Sky Abyss contains the Nova Proxy, Echo of Legion, Echo of Virtua, Ascended Oversight, [[spoiler:Cracky the Sky Queen]], [[spoiler:STORM Boxxyfan]], and the [[spoiler:[[TrueFinalBoss Legion Singularity]]]]. Fighting them isn’t necessary to beat the game, but it’s what leads to the [[GoldenEnding best ending.]]
* ''VideoGame/AngryBirdsEpic'' has two:
** The more obvious one comes after getting the submarine. Tapping on the whirlpool takes you to the level "Maelstrom" where you can battle the Poseidon Pig, who has more health than the FinalBoss.
** There’s also the "Mouth Pool" level, a ten-phase wave battle against a Necromancer Pig who summons virtually every undead pig in the game. It’s only on the tenth wave that the Necromancer Pig fights you directly.

** Izaro lies in [[MarathonLevel the Labyrinth]]. He hits hard and is always assisted by his Goddess who attacks independently from him. He's fought in three stages. The first two adds a gimmick that changes daily and need to be dealt with if you don't want it to carry over to the next phase and the last phase is in a room filled with traps. He's well worth the challenge if you want the power of those Ascendancy Classes. Also inside the Labyrinth is his pet Argus, who may as well be considered one due to how hard he hits.
** The Shaper was the TrueFinalBoss of the post-game map content, and his domain was guarded by four of the bosses in the highest tier maps in the game. The ''War for the Atlas'' expansion adds a ''very'' True Final Boss: a DuelBoss with the Shaper and the Elder, fought after defeating the Shaper and then spreading the Elder's influence to the Shaper's guardians and then defeating the Elder's guardians. In ''Conquerors of the Atlas'', Sirus, Awakener of Worlds, replaces him as the final map boss. ''Echos of the Atlas'' added a second seperate final boss, the Maven.

* The ''Videogame/{{Yakuza}}'' series has Jo Amon and the other members of the Amon Clan, a group of assassins that will challenge you once you complete every substory in the game, even in the spinoff titles. Defeating them earns you a pair of their SinisterShades, which increase the amount of damage done by weapons.

** The Steam release of the fourth game has a whole area dedicated to these, featuring upgraded versions of the main game bosses (except the final boss), the notorious Cosmic Monolith from the third game, and even [[spoiler:evil versions of your party members]]. [[LegacyBossBattle Some of the bosses from the second and third games]] also return in the main game as optional minibosses.

* The ROMHack ''Super Mario RPG Armageddon'' adds a ton of NintendoHard bonus bosses, including [[VideoGame/FinalFantasyIX Ozma]], [[VideoGame/FinalFantasyX Penence]], [[VideoGame/FinalFantasyXII Yiazmat]], [[VideoGame/FinalFantasyVI Goddess, the Elemental Dragons, Kaiser Dragon]],[[VideoGame/FinalFantasyIVTheAfterYears Mysterious Girl]], [[VideoGame/SuperMarioGalaxy Rosalina]], [[VideoGame/PaperMarioTheThousandYearDoor The Shadow Queen]], [[VideoGame/ChronoTrigger Magus and Schala]] (as a DualBoss), and the two most powerful bosses of all: [[spoiler: [[VideoGames/KingdomHearts358DaysOver2 Xion]]]] and [[spoiler: [[VideoGames/FinalFantasyVI Terra]]]].

** The Shaper was the TrueFinalBoss of the post-game map content, and his domain was guarded by four of the bosses in the highest tier maps in the game. The ''War for the Atlas'' expansion adds a ''very'' True Final Boss: a DuelBoss with the Shaper and the Elder, fought after defeating the Shaper and then spreading the Elder's influence to the Shaper's guardians and then defeating the Elder's guardians. In ''Conquerors of the Atlas'', Sirus, Awakener of Worlds, replaces him as the final map boss.