History ThatOneBoss / MegaMan

* Ring Man has a highly unorthodox pattern to his ring tosses, employing a ConfusionFu strategy to trick players into dodging into the rings due to how Ring Man jumps to catch them or jumps to toss them and catch them on the ground. Like Shadow Man, the battle requires specific maneuvers to each attack pattern and there is little room for error thanks to Ring Man dealing heavy damage, especially [[CollisionDamage from a body blow]]. Fighting him without his weakness is especially a "learn or die" experience.

* Quick Man, right after his own [[ThatOneLevel hair-pulling level]]. He is incredibly fast, but can still deal a respectable 4 damage per hit both with his body and his homing spread of Quick Boomerangs. While Flash Man's Time Stopper can take half his life in one shot[[note]]"one shot" meaning its entire weapon energy supply[[/note]], the player will probably need it to get past the daunting laser barrage right before his door. The Crash Bomber, his other weakness, is notoriously slow, inefficient, and cumbersome (and probably not available at all in the rematch). This was enforced by the dev team, who initially conceived Quick Man as a rival character and thus made him extra difficult to beat, to the [[{{Pun}} point]] that the boomerang on his head sticking out of his mugshot frame on the stage select screen is meant to be indicative of his high difficulty compared to the other seven Robot Masters. What isn't intentional, though, is that on top of all of the above, Quick Man's attack pattern is bugged; he's ''intended'' to make three jumps and throw his boomerangs during the second jump, but if he gets stuck on a wall, which he tends to do, he often skips one or more of his jumps and goes straight to the boomerangs.

* The Doc Robot that mimics Quick Man is just as fast and unpredictable as the original Robot Master, but is also [[LightningBruiser larger and more resilient]]. He also deals far more CollisionDamage (8, as opposed to the original Quick Man dealing 4), and due to the way that he runs and jumps all over the place, it's extremely difficult to avoid bumping into him. This is such a deadly threat that a common strategy is to get hit by his Quick Boomerangs ''on purpose''; they deal far less damage, and the resulting MercyInvincibility can be used to avoid a devastating collision.
* The Doc Robot that mimics Wood Man has a Leaf Shield with a significantly larger hitbox than that of the original Wood Man's to match his larger build--large enough that you'll need to either do a pixel-perfect leap over it, or use Rush Coil (which consequently [[MortonsFork smacks you into the leaves coming from above]]). The Leaf Shield also deals a whopping 8 damage, as does direct contact with Doc Wood himself, meaning that he can very easily take you out in just 4 hits.

* Halfway into King Stage 2, the game's first MarathonLevel, you'll encounter King Plane, a simultaneous PlatformBattle and AutoscrollingLevel over a BottomlessPit. The Plane not only [[InterfaceScrew does not have a visible health bar]], but will also take any opportunity to send you plummeting to your death with its two main attacks: an unavoidable screen-clearing laser that takes many shots to cancel out and can wipe out nearly a third of your health on hit, and a RocketPunch that not only homes in on your position, but will destroy any platform it connects with, easily killing you if you're unlucky. While the boss is generous enough to [[BossArenaRecovery constantly provide power-ups in bubbles during the fight]], they are mixed in with [[BlindedByTheLight flashbangs that white out the screen for about a second]], more than enough time to slip into the abyss. Its weakness as Mega Man, Spread Drill, is difficult to hit it with due to how the boss bobs up and down, and its weakness as Bass, Treble Boost, drains energy very quickly during use and has to be bought from the shop for 200 bolts beforehand. If you die, [[ContinuingIsPainful it's back to the beginning of the mini-stage that comes before it as well]].

* The final battle against the Wily Machine in this game is an arduous task. It's one of three battles in the main Classic series that are ''three'' phases back-to-back with no breaks in-between[[note]]the first being the Wily Machine from ''6'' and the second being the Mega Mech Shark from this game; however, the former is widely regarded as an AnticlimaxBoss, and only the third and final phase of the latter is seen as overly difficult[[/note]], technically giving it the status of a MarathonBoss. It also comes directly after the traditional series BossRush, so if the player has exhausted all of their weapons' energy on the Robot Master rematches without an M-Tank to spare, things can get ugly. All three of his phases have their own problems as well: the first phase is a TennisBoss with large, bouncing eggs that take many hits to detonate and can only hurt him in his jaw, the second phase has powerful stomping and ramming attacks as well as a flame jet that can be extremely difficult to avoid, especially at close range, and the third and final phase, the Wily Capsule 9, is a heavy user of TeleportSpam and quick, deadly projectile patterns from anywhere on the screen with a weakness to Plug Ball, a weapon that is nigh useless against airborne targets.

* Armored Armadillo on ''Maverick Hunter X'''s Hard Mode, where he picks up an attack where he [[BeTheBall bounces off the walls]] ''and'' fires off bullets in four directions. Even if you use the Electric Spark to take out his armor, it's still hellish. If you're playing as Vile in ''MHX'', you ''will not'' have Peace Out Roller (the same thing as Electric Spark, except it's lobbed instead of shot) for when you fight him, because its [[TheKeyIsBehindTheLock weapon type is locked until you beat him]]! That's right, you unlock a boss's weakness by defeating that boss. To make up for this, he's also weak to the fist weapons, which you ''do'' get from Spark Mandrill; however, they don't remove his armor.
* The first boss of Sigma's Palace, the Bospider. This boss has a peculiar movement scheme[[note]]based on a popular Japanese lottery system called [[http://en.wikipedia.org/wiki/Ghost_Leg amidakuji]], or "Ghost Leg"[[/note]] - there are four poles at the center of the screen, and "bridges" appear at random between them to determine what path Bospider will take down to the floor, where it will then briefly expose [[AttackItsWeakPoint its weak point (the center of its abdomen)]] and quickly zip back up to the ceiling to start again. The problem is that you're given a very short time to see where the bridges are laid out and determine what path it will take, and not only does Bospider get faster and faster as its health goes down, but [[WeaponizedOffspring it also occasionally showers down miniature spiders called Petitpiders]] that can both absorb any shots coming Bospider's way and damage you before you can shoot at it. More often than not, you'll try to get your once-per-pattern shot in only for a Petitpider to get in the way or for Bospider to slam down on you for heavy CollisionDamage, making the fight much longer and more difficult.

* Although the second encounter with Violen in the first stage of the X-Hunter Base can be tricky with his unpredictable mace ball, he pales in comparison to the boss of the following stage, the Serges Tank. The entire fight starts on [[PlatformBattle four vertically moving platforms]] over a floor of OneHitKill spikes, and you're only given around half of the screen to fight against it - the rest is taken up by the Tank itself. Its arsenal is fierce: the first phase consists of four durable vertically-placed cannons firing fast projectiles that either go straight forward or bounce along the floor. Once they're all destroyed, Serges reveals himself... but not before [[AdvancingBossOfDoom inching forward and destroying two of the four platforms]], leaving you with ''even less'' space and footing. Serges will then start moving up and down erratically while firing projectiles that alternate between exploding into Xs or +s. To make matters worse, not only is Serges [[AttackItsWeakPoint only vulnerable on his top half]], but he also tends to get very close to the spikes below, so even one mistake can result in a very difficult battle having to be restarted from scratch. The only saving grace is that you can skip the first phase destroying the four cannons with a [[SmartBomb fully charged Giga Crash]] at the beginning, leaving Serges exposed to your attacks, but even then, good luck landing hits on him.

* While Sigma himself is very pattern-based and easy to read, the true terror appears in the form of Kaiser Sigma, his gigantic battle body. Kaiser Sigma is so large that he fills up half of the arena you fight him in, and his weak spot is [[HitboxDissonance not his head, but rather the small "fins" directly above it]]. He has two patterns, one when you're behind him and one when you're in front of him. When you're behind him, he shoots [[MacrossMissileMassacre many homing missiles that hit extremely hard]], and when you're in front of him, he charges and fires a cone-shaped laser either upward or downward that [[CycleOfHurting continuously damages and stuns you when you get hit by it]]. All the while he's spawning tracking bombs. Only two things can damage him: charged X-Buster shots (in a game where the X-Buster upgrade actually [[PowerUpLetDown makes it more difficult to use]]), and the [[GameBreaker Game-Breaking]] Z-Saber, which can take him down in only two hits, but get hit ''once'' while trying to slash him, and it'll be cancelled out. Even after you manage to kill him, it's not over, as you still have one last trial: wall-climbing a long vertical [[AutoscrollingLevel autoscroller]] with the Sigma Virus trying to knock you into the damaging lava below. If he successfully manages to, it's entirely possible for you to get stuck in hitstun under one of several outcroppings in the shaft, and since the lava is treated as a solid floor, you can get crushed, in which case [[ContinuingIsPainful it's back to the beginning of Sigma's first form]].

* Isaz and Sowilo, the tank boss at the end of the second fortress stage; it has two faces that must be destroyed to be defeated, and both require the usage of both characters to hit. Sounds awesome, right? '''WRONG.''' The tank takes up a ''good'' portion of the screen, and spends ''much'' of the battle restricting your movement space on the very left edge of the screen on top of the moving platform, and can only be pushed back by using Zero's Saber or if enough time passes. The upper face shoots a set of three energy balls that are almost impossible to dodge, while the lower face shoots a missile upwards that then comes down on your position. Between this, and the fact that the projectiles actually ''move with the boss'' when Zero pushes him back, and you have one of the more poorly coded bosses since the Buebeam Trap from ''VideoGame/MegaMan2'' and Doc Robot's Wood Man form from ''VideoGame/MegaMan3''.

* Fighting The General as X is [[BreatherBoss an utter cakewalk]], as he can easily hug the opposite wall and plug Charge Shots into General's face while dodging generally slow-moving projectiles. The General for Zero, on the other hand, degenerates into this quickly since Zero has no effective long-range attack for a safe option, forcing Zero to close the distance to hit his head. It should also be mentioned the game registers CollisionDamage if bodily contact is made with General's ShouldersOfDoom or even his body in general, and he hugs the wall he chooses to be by close enough it's suicide to try and WallJump behind his back to hit him in the head. The only two options Zero thus has involve either riding on The General's RocketPunch back to his body while dealing with the previously-mentioned projectiles, which despite their speed require fast reaction times to avoid since Zero is unavoidably coming ''closer'' to them, or to hug the opposite wall and wait for The General to charge in close before leaping off and plugging him with a rolling slash. The latter is the safer method, but depending on how General's AI runs it can take a ''long'' time to wear him down this way depending on how often he feels like pulling said move off.

* At the end of the next stage, you'll encounter Rangda Bangda W, a souped up version of the second fortress boss from the first ''Mega Man X''. All three colored eyes it has have different attacks, and none of them are particularly troublesome - it's very similar to the original fight. It's when the boss reaches half health that things get ugly. Starting from that point, the boss is able to deploy OneHitKill spikes ''on the walls'' as well as the floor, including directly where you are - be in the wrong place at the wrong time and it's all over, sometimes before you can even realize because your character's sprites cover the walls. A common strategy against this is to get to the fight with X's Gaea Armor equipped, as it is invulnerable to spikes, doesn't slide down walls, and has a heavy damage output, in which case the boss becomes no problem... but the inability to dash makes the level one.

* The fight with Gate is a TennisBoss and PlatformBattle hybrid over a BottomlessPit while he constantly gives chase and occasionally[[note]]often to the point of making the fight excessively long[[/note]] fires off random colored "gates" that have various detrimental effects[[note]]red ones slow you down, orange ones fire at you, green ones home in, blue ones have a vacuum effect, and purple ones generate [[DemonicSpiders Nightmare Viruses]][[/note]]. The only way to damage him is to attack the "gates" so they split into smaller projectiles that can hit him, but they can also damage ''you'', so you'll often find the both of you taking damage simultaneously. The red and blue "gates" are by far the most dangerous, as they greatly increase your chances of falling into the pit or getting knocked in. When he gets below half health, he gains an additional attack: ''breaking the platforms that you need to stand on to survive''. Not only can it easily kill you, but it also doesn't allow you to hit him in return. This fight is tedious, dangerous, and overall very frustrating.[[note]]Playing on Rookie Hunter mode in ''[[CompilationRerelease Mega Man X Legacy Collection 2]]'' adds an indestructible floor over the pit, but it only makes the fight easier by so much.[[/note]]

* [[spoiler:Lumine]]. He comes after ThatOneLevel, and is fought directly after Sigma, who's hard enough to begin with. He has two forms; the first one uses the Overdrives of the first 8 bosses, except some are modified to last longer; when Burn Rooster's attack comes out, it lasts for the duration of the match. In other words, once it happens, the walls are off limits. Additionally, he himself is always moving, making it hard to hit him. Once you've drained his health, he enters the second form, which has a multitude of {{Bullet Hell}}-like laser attacks (one of which lasts a long time and then ''comes back in reverse''), has no notable weakness, and is difficult to get a bead on. On his trump card, he triggers [[DesperationAttack Paradise Lost]], which will outright [[RocksFallEverybodyDies finish you off]] if you don't do the same to him in 30 seconds. And the player has to know they had to [[spoiler:[[GuideDangIt have Axl finish him with a Doubleteam as a prerequisite for the secret ending]]]]?

!!''VideoGame/MegaManZero''

* Kraft from ''Zero 4'' is a nightmare to fight against. The grenades, the laser rifle that requires you to dash underneath it with split second timing, the giant knife that damages you as it throws you across the arena causing damage depending on how far you were flung (which can be heavily reduced with armor that prevents knockback [[Main/GuideDangIt not that the game tells you this]]), the missiles, and the fact that he's one of the few bosses willing to get right directly up in your face on a non-scrolling single-screen battlefield are awful. Also of note is him having 3 full bars of health. The only enemy with the same amount of health at that point was the huge BackgroundBoss! He's also fought in an open area with no walls, so there's no wall jumping away from him.

** He is invincible at all times except when moving or attacking, moves like a spastic monkey on crack so that his vulnerability then doesn't even matter, and his attacks are irritating to dodge, because [[ShapedLikeItself Quick Boomerangs are really, REALLY fast moving]]. It doesn't help that he's the second boss of the game, the first boss was a complete chump, and the next boss AFTER him isn't exactly threatening either, so he's not even really a WakeUpCallBoss... Worse yet, it's ''entirely'' possible for the game to be UnwinnableByMistake here, as you can't leave his area (either to recover HP or improve your moveset) once you enter (but nothing stops saving...)
** Quickman [=V2=] will likely be the first “ghost” boss Navi you fight (a stronger replica of the original that can employ new tactics and gives you a summon chip upon defeat, found on hidden squares in the net), showing up on the way to [=KotoSquare=] on a dead end path. Now he can use two boomerangs in rapid succession and, when he gets low on health, will zip over to your side to use a [=WideSword=]-esque move. Since you have to know in advance you’re going to fight him, you may not have saved, which can truly screw you if you’re just casually exploring the new area (plus his new tactics can leave you unprepared even if you had a good system on the first bout). Beat Quickman [=V2=] and you’ll have a chance of running into ''[=V3=]'' in the same zone (which could be as soon as completing same task that caused you to run into [=V2=]), who has even more HP and even ''more'' new strategies (among others his boomerang can now be thrown in a wave pattern, making it much harder to dodge).

%% Rogue SX or Apollo Flame don't actually count, no matter how much you want to add them; Bonus Bosses are overpowered on purpose.

[[folder:Fan Games]]
Due to the myriad of tough bosses it has, ''VideoGame/MegaMan8BitDeathmatch'' has [[ThatOneBoss/MegaMan8BitDeathmatch it's own page]].

!!''VideoGame/StreetFighterXMegaMan''
* As if his [[ThatOneLevel stage]] and [[GoddamnedBats choice of enemies]] weren't annoying enough, Dhalsim can really give Mega Man a run for his money. His strategy revolves around TeleportSpam, and he loves to either telefrag you outright or catch you at weird angles before assaulting you with long-reaching, lighting-quick punches and teleporting away before you can counter attack. His worst attack though is his fire breath, which has ''scary'' range and sends damaging embers flying ''everywhere'' in front of him. It's incredibly awkward to dodge, and you're nearly guaranteed to take the hit unless you can anticipate it coming and get out of the way before he lets loose.
* Vega (Claw) only uses melee attacks, but he's [[LightningBruiser very fast, deals heavy damage]], and is only weak to a melee attack. He also has ThatOneAttack where he leaps onto the railing and tries to slash down on you, and it's very hard to dodge if he performs it in the middle of the arena. In fact, the move you ''want'' him to use is his Limit Break, which isn't too difficult to dodge and leaves him open in the center after it ends.
!!''VideoGame/MegaManUnlimited''
* Jet Man. He spends most of the fight out of your reach, and he has lightning-fast missiles and a whole cargo load of bombs in his arsenal that require precision and perfect timing to avoid. Good luck doing a NoDamageRun against this guy!
* Glue Man fights a lot like Concrete Man from ''Mega Man 9''. He fires Glue Shots at you to freeze you while at the same time sliding all around the arena trying to ram you for MASSIVE CollisionDamage.
* Comet Woman isn't too bad in her first fight, but she becomes exponentially harder in the BossRush. Without the low gravity from her stage, she's able to move much faster, her orbiting shield attack becomes harder to avoid, and you'll spend more of the fight with those orbiting balls around you blocking your shots.
* The GiantEnemyCrab from Occupied Wily Stage 1. It pays homage to the Mecha Dragon from ''Mega Man 2'', but ramps the difficulty UpToEleven. You have to use the three ladders to avoid the energy balls the crab shoots out, but it also has another attack where it electrifies one of the ladders. If you get hit by anything while you're on the ladders, the knockback will push you right into the pit, and there's no safety platform like the Mecha Dragon fight.
* The squid boss from Occupied Wily Stage 2 has a OneHitKill move where it rams its head (which you have to stand on in order to fight it) into the ceiling, and it requires a precise jump off to the side of the boss gate in order to avoid it. The later you jump, the more likely you will be to hit the ceiling and fall into the pit, but if you jump too early, the squid will be too high to catch you. Even then, you're still fighting it on a small platform with bubbles from its mouth and plasma balls from its tentacles, making it very easy to get hit and even then you could still get knocked into a pit.
* The Wily Machine is probably the hardest version of Wily since his capsule from ''Mega Man 7''. The first phase has a weak spot that is out of reach of the Mega Buster, so you need an upward-reaching weapon to hit him, and he takes up about ''three fourths of the screen'', giving you little room to dodge his attacks.
** The second phase is even worse. The Wily Walker's weak spot is only visible for a couple seconds when it jumps, and it's random where it's going to jump next. Each time after it jumps it will charge at you. If it jumps all the way to the other side of the arena, it will dash at you, and you can slow it down with the Mega Buster in that case, but if it lands somewhere in the middle it will just walk at you which can't be slowed down. If you're not behind it when it does this, you need a perfectly-timed Comet Dash or Rush Coil to avoid it.

!!''VideoGame/MegaManRevolution''
!!! Original
* Saw Man is extremely erratic and unpredictable, due to the lack of a pattern. He jumps around a lot and throws out Iron Saws which are highly damaging. His weakness, Acid Bubble, is extremely tricky to hit him with due to him jumping a lot.
* The first phase of [[spoiler:the Remir Machine]]. The only way to damage it is to turn on the spikes in the room and get it to step on them, while at the same time avoiding its two massive hitboxes and the bullets it fires from the top of the screen, and also making sure ''you'' don't fall into the spikes.

!!''VideoGame/MegaManRockForce''
* Virus Man can reverse your controls ''and'' disable your charge shot if contact happens with any of his viruses or himself. His attack where he separates from his legs can be particularly bad as unless you dodge it, you're getting infected. Charade Clone, his weakness, also triggers his MercyInvincibility upon damage, so you can't just spam it.
* Shock Man's second battle can be annoying due to the battle essentially being an electric jump rope where ''all'' of his attacks force you to jump repeatedly, and with good timing to avoid taking damage, and ''every time'' he lands on the ground, he shocks the entire floor. One of them even has him jump then bounce three times in succession, each time he lands triggering the conductive floor.
* While Pulse Man's attacks aren't all that painful, he can make situations where it's nearly impossible to dodge at all if he throws out ''four'' bouncing projectiles that take up a good amount of space on the screen, coupled by the fact that all of his jumps are {{Shockwave Stomp}}s and also having a large projectile that removes whatever dodging space you had left.
* Charade Man's fighting style revolves around making the player frantically jump and slide around for dear life as he floods his arena with annoying projectiles. The blue balls he throws are annoying enough, since they can't be destroyed and will explode into a few smaller projectiles after a while. But the red ones are where things go from annoying to nightmarish: no matter if the player ignores or destroys them, they release a Charade Man clone upon detonating which will begin hopping around and absorbing shots meant for the actual Charade Man. They take quite a bit of punishment before dying, and if you lose track of the original Charade Man then there's no way to tell him apart from the fakes. Even fighting him with the Crypt Cloak, his weakness, isn't a safe bet since he can easily leap over the shockwaves it creates.
* The Fusion Masters that you fight is dependent upon which one of the first eight you defeat last; meaning you may or may not have to fight War Man, who fights somewhat like Sigma from the first ''X'' game. He has a shield that allows him to deflect any attack other than Crypt Cloak (even his Rock Force weakness, Knight Crush, gets deflected), and this shield is only put down for a second when he attacks (which he will only do if you get within a dangerously close range). He's too big to jump over, and deals ridiculous amounts of damage with his attacks. He also deals a lot of contact damage, and can easily stick you in a corner if you're not ready for a fight against what is basically a giant Sniper Joe. Also, if Crypt Cloak is spammed, he'll jump all over the room and cause quakes, potentially stunning you.
* If you don't get War Man, the other (original) set of Fusion Masters has a nasty fight in Flare Man. Similar to Stone Man from ''Mega Man 5'', he jumps around the room, stunning you whenever he lands unless you jump. ''Un''like Stone Man, ''his other attacks'' also stun you when he starts them, which can really mess up your timing when dodging them. He's also one of a few bosses who's actually harder to fight with Mega Man than his Rock Force weakness; Crypt Cloak is hard to hit him with because it's ground-based and he jumps around a lot, but Nitro Man can throw the Wheel Cutter in multiple directions.
* Regardless of which set of Fusion Masters you fight, once you beat all four your next stop is Death Man. He's not a very complex boss but he makes up for it by doing ''absurd'' damage with his attacks, which kill from full health in just three hits! To make things worse, he's weak to the Charade Clone which is hard to actually hit him with due to his scythe being capable of destroying it before it even hits him.

!!''VideoGame/MakeAGoodMegaManLevelContest''
* The Tier 2 boss in the original version is Dagger Man, who is every bit as hard as he was in ''Super Fighting Robot''. He loves to teleport all over the place and can easily telefrag you for cheap collision damage, his cutting waves come out fast with little to no warning, and his nastiest attack is him shooting daggers to the floor and creating shockwaves like in his game of origin, only at a far greater rate. It's ''incredibly'' hard to keep up with all the daggers and shockwaves, and he loves to spam it. He loses this status in the remake where he's easier despite being bumped up a tier.
* The boss of Tier 4, Justice Man, is a complete inversion from Dagger Man. In the original release he was decently tough but otherwise fair, but he became a lot more annoying in the remake. His attack pattern is still manageable... in his first phase. There's now a second phase to his fight where he heals himself back to full HP and adds a ''second'' Justice Man to the mix. While his attack pattern is still the same, fighting two fast, powerful, independently-acting Robot Masters at the same time is frustrating and disorienting and it's easy to run into one Justice Man's attack while dodging the other.

!!''VideoGame/MakeAGoodMegaManLevelContest 2''
* The three bosses of the [[ThatOneLevel notorious]] Yggdrasil level are just as fiendishly difficult as the stage itself for all the wrong reasons: unnecessarily huge health pools, unpredictable AI, and incredibly unfair attacks. It's worth noting that in a game with more than its fair share of difficult bosses, they're among the few ''outright excluded from the arena challenges'' due to being so ridiculously annoying to fight.
** Crator is considered to be the toughest of the three by far. He spends a lot of time deflecting your shots, is incredibly aggressive and loves getting in your face, and has attacks that lop off around half your health at best or one-hit kill you at worst. Even his weakest attack, a series of energy bursts shooting up from the ground, makes up for its lacking strength by coming out fast and being incredibly hard to dodge. To make things worse, his weakness to the Slash Claw does little to mitigate the difficulty of his fight since its lack of range means you have to constantly put yourself in the danger zone to use it.
** Cream is no slouch either, since she has an instant death attack of her own that comes out way too fast for its own good. She also loves to jump around the arena like a spastic monkey, and has a ton of different projectile attacks that can be hard to dodge since she has no tells indicating what she'll be firing at you.
** And while not as bad as the above two, Kichona is annoying to fight all the same. Most of it is for reasons that would normally make her more of a GoddamnedBoss, such as having two health bars and being able to heal herself with her syringe attacks. But what truly puts her in this category is the fact that she can randomly glitch herself out of the fight and make it ''impossible'' to win.
* While severely toned down from how ridiculously hard he was in his [[VideoGame/RockmanCX home game]], Cheat Man is among the hardest tier bosses. He can hit you with damaging text before the fight even begins, and spends the entirety of his boss battle behind a shield that drops your attacks on you if you end up hitting it. He also constantly has large projectiles bouncing around his arena, which he will happily attempt to glitch you into falling into them multiple times in a row. Even worse, he has a powerful OneHitKill beam attack that will still cause you to drop to one health if you have the Skull Amulet equipped, and there's a delay before firing just to trip you up.
* The boss of Tier 7, [[spoiler:Future]], is a doozy. He starts off with projectile spam by spawning scythes at random spots on the map that home in on you. It's tough to deal with but manageable... until he randomly slows you down with his hourglass attack, making it way harder to dodge his scythe onslaught. And when you deplete his health, it takes him a while to ''actually'' die and he starts spewing fire all over the place that can easily finish off a battered player.
* Autobounce, the boss of Wily 4. Good news: You get unlimited ammo on all your weapons for this fight. Bad news: Autobounce can only be hurt by one at a time, represented by its color scheme (which changes after each time it takes damage). Its attack in the Grab Buster form heals it if it connects with you, the Sakugarne form is nigh-impossible to hit without taking damage, and the Slash Claw form moves faster and faster until you're able to hit it (which, again, is near impossible to do without getting hit yourself). Plus, as its health goes down, its attacks and movements get faster.
* Chimera Bot 1 combines Joe Man and Bond Man's abilities, resulting in a spastic boss who constantly leaps around the arena while protecting himself with a giant shield, and can limit your movement by slathering glue all over the ground. And when he traps you, and he ''will'', he's quick to follow up with attacks that are tough to dodge, such as the long-reaching splash damage of his glue mines as well as the quick-falling glue drops from the ceiling. While Slash Claw can penetrate his shield, it does so little damage against such an aggressive boss that it doesn't really matter.
* Chimera Bot 4 (Force Man + Match Man) combines Match Man's insane speed and tendency to fire off quick-moving fire waves every time he lands after his frequent jumps with Force Man's hard-to-dodge force beams. Unsurprisingly, plenty of players consider him to be the hardest of the Chimera Bots hands down.

!!''Make A Good 24 Hour Mega Man Level''
* Quick Man is a default devkit boss for the [=MaGMML=] series from this game onward, but the devs toned him down a little bit by fixing the AI issues that caused him to break from his tough but learnable attack pattern and devolve into an unpredictable, spastic mess in ''Mega Man 2''. However, his boss fight in the level ''Breaking Ground'' is still insanely hard for different reasons: his boss fight takes place on rows upon rows of destructible Chill Man blocks, and ''any'' movement whether it's walking, jumping, or blasting will break them and mess with the elevation. This completely ruins the flow of the battle making it fiendishly hard to safely hit Quick Man while he zips and leaps around all over the place while he puts the hurt on you. The fight can ''really'' drag on, and if you run out of blocks for footing, you get dropped into a pit infested with enemies that will kill you in seconds.
* Giga Count, the boss of Wily Stage 1 spends most of the fight out of reach while having several smaller versions of himself bombard you with annoyingly accurate lasers. When they disperse, you're supposed to shoot him by jumping across several count bombs as platforms, but getting in a hit is ''aggravating'' since the bombs shield Giga Count from damage, and will kill you instantly if they press you against a wall. His weakness, the Water Wave, is also a pain to use against him because of its limited vertical reach, and using it against him when he's on the ground isn't safe since he'll send a few explosions your way until he's back in the air.
* The second and fourth phases of the Wily Machine Arc are ''brutal'', and pit you up against swarms of Wheel Cutters and rocks that are quick to overwhelm you while you're trying to hurt Wily. Even with forced Time Slow usage in the last phase, the rocks are still so fast and numerous that merely getting in a hit on him is an uphill battle.

!!''Make A Good Mega Man Level: Episode Zero''
* While the first two phases of Wafer Wagon aren't too difficult, the third phase is brutal as it's also an auto-scroller over a bottomless pit. Its projectiles can be hard to see against the background, too, and it's all too easy to get dunked into the pit and have to start the whole fight over.

!!''VideoGame/MegaManSuperFightingRobot''
* Dagger Man is a particularly nasty case of this. His attacks involve the use of his Flash Daggers, and they deal tons of damage. You will most likely get hit by his attack where he dashes and then sends cutter waves two times. It's very easy to be hit by this attack. Even with your Mega Buster's charged shot upgrade that can be bought, Dagger Man has another trick up his sleeve; he also teleports before two of his main attacks and after he shoots his Flash Dagger, meaning if you don't have his weakness, this teleportation can be annoying if you've charged up your Mega Buster and he teleports away from your shot, (even when he teleports right behind you) even when he is about to use his dash attack. There is also the attack where he shoots three daggers down, and it is easy to get hit by the dagger he shoots down while you are avoiding the shockwaves, leaving you screwed.
* Axe Man, even with his weakness to the Flash Dagger, can utterly destroy you. He mostly jumps around and stomps, which can stun you if you're on the ground. He can also not only use his Giant Axe, but also send three projectiles towards you.
* The boss of Wily 2. It moves in a circular motion, and sends out very hard-to-dodge attacks, like green mines and a laser. While those are dangerous, the [[CrosshairAware crosshair]] that was pestering you throughout the whole stage still attacks you here, making it even more difficult.

!!''VideoGame/SkullmanInScoobyDoc4TheDestroyerFeaturingAtsushiOnita''
With the majority of this being a BossGame, this is a given.
* Redskull is your first major challenge. He fires out giant homing fireballs, then uses some homing shots, and then uses some almost-undodgeable lasers. Whilst you can use the Seeker Missiles to make it somewhat easier, it won't do you much.
* The core of Albatross. Not only is it the boss of a very hard shoot-em-up level, the fight essentially boils down to BulletHell. Oh, and if you destroy it, you need to dodge one last attack from him that is a OneHitKill no matter what.
* Atsushi Onita, the penultimate boss, can be a true hair puller. His attacks (throwing fluorescent lights at you, sending down a lightning bolt to cause fire to appear, and dropping crosses on you) are [[RandomNumberGod completely random]] (except for the crosses), not helped by the fact the shadow teleportation attack is random as well, and the fact that the fluorescent lights cause an eight-way projectile when they explode.

!!''VideoGame/MegamanRevengeoftheFallen''
* Tornado Man tops this list above all other bosses by sheer instant-death factor. The layout of the room has two platforms that rise up with every Tornado Blow the boss does revealing bottomless pits underneath that players can easily fall into when avoiding his attacks. The platforms also rise up to a spiked ceiling that can also one-shot you if you're not paying attention. To make matters worse, his Tornado Blows are random, so there is no predicting where they'll rise up from the ground. Finally, he can spawn and spam slow-moving clouds that track and home in on you and upon colliding with Mega Man, will slow down his movements drastically, making all of the above a rage-inducing chore.
* Star Man is not as bad as Tornado Man, but since he has a high percentage change of warping away from damage against anything other than a lemon shot from your buster, he is quite annoying. Every time he warps away from your attacks, he will call a meteor shower that gets worse the less health he has, making it near impossible to dodge at half health or less. He also can unleash his Star Crash barrier in a variety of ways to include one way where it spirals out quickly with no tell and it is near impossible to dodge.
* Punk, the Mega Man Killer. He can appear up to two times in the game and is notable and remembered for only one thing only: his 5-pound stunning attack where he homes in on your current position and slams down on you. If you happen to be on the ground when he hits, you are stunned for the entire duration of the attack and could be hit up to two additional times, causing many a rage-filled game over for players.

!!''VideoGame/MegaManRockNRoll''
* Reactor Man. His main form of attack is a highly damaging laser that he uses quite a lot. Sometimes, he'll point it up to the ceiling while in the air, causing projectiles to come from the end of the beam, and then come down to do a ground-pound attack that causes a whole bunch of projectiles to spawn.
* [[VideoGame/MegaManSuperFightingRobot Dagger Man]] appears in this game and he's even worse than he was in his home game, as he's way faster and very unpredictable, meaning you'll constantly get hit, not helping matters is the high damage output of bosses. Trying to get the GoldenEnding? Good luck.
[[/folder]]

[[folder:ROM hacks]]
!!''VideoGame/RockmanCX''
* Fire Mario, on top of being very quick, is capable of [[CycleOfHurting stun-locking you]] and draining your health very quickly through use of his GoombaStomp attack, which he can do more than once in one quick swoop if you're not careful. If he traps you in a corner, [[YouAreAlreadyDead you're pretty much done for]], even if you use E-Tanks.
* Cheat Man, for obvious reasons. Between having a large array of OneHitKill options, he also gets gradual HP recovery and a move where if you shoot him as he ascends upwards; he'll teleport you right in from of him so [[HoistByHisOwnPetard you get hit instead]]. Once he brings in the ''[[Videogame/Mother3 MOTHER 3]]'' instruments for his BossRush rematch, the fight only gets more obnoxious. To make it worse, his weakness is the Rock Buster, but the only way to take advantage of this weakness is to use a charge shot on him, and even then he can restore his HP, and sometimes ''switches health bars''. Oh, and don't try and beat him with Cheat Saber in the refight, as he'll reverse it on you.
* [=Rockman/Mega=] Man is able to drag out his battle through use of digging through his own personal Pause menu to swap to another weapon (which is invisible to you) or use an E-Tank to completely restore his health. God help you if he decides to bring out the Crash Bombs which [[StickyBomb latch onto you]] and will completely destroy you if you don't shake it off.
* Kamen Rider is a real hair-puller. He starts the fight on the Cyclone, and, throughout the battle, switches between ridng the Cyclone or fighting on foot. Though the Cyclone is easy to dodge, good luck when he's on foot. He spends most of his time jumping around and trying to grab you. If he does end up grabbing you, he uses Rider Kick to knock you back very far from him. His jumping Rider Kick can also knock you back far as well.
* Air Man. He likes to teleport around the arena and fire out tornadoes. He can also split himself into other tornadoes and reform that way. What makes this worse is his weakness: Ringo Shield. In order to even hit him with the weapon, you have to use the projectile that you can fire at the cost of losing the shield, but since he likes to go into the walls and sometimes too high to even hit him, this can waste your weapon energy. On top of that, there's spikes on the sides, and combined with the fact that the wind is blowing, [[YouAreAlreadyDead you'll probably die if you stand still at the bottom of the arena]].
* [[spoiler:Dr. Light. His arsenal of attacks is copied from [[Videogame/StreetFighter Ryu]], and ''boy'' do they hurt. His {{Shoryuken}} is easily the deadliest of his attacks, being able to 2HKO you at full health, while his HurricaneKick can launch a brief CycleOfHurting that guarantees your death if you get locked into it with low enough health.]]
** Same goes for the [[spoiler:giant Dr. Light, who serves as the final boss and ShoutOut to ''[[VideoGame/SuperMarioWorld2YoshisIsland Yoshi's Island]]''. This is a long, long fight, as he has a boatload of health and no visible health bar on-screen. He starts by destroying two parts of the platform you're standing on, and then he can use a Hadouken-like attack, get up close to punch you, and later on, teleport, destroy parts of the platform again, and then can summon rocks to drop on you. The only weapons that work are Power Bomb (which you have to throw at the right time to hit him) and Print Cutter (which makes it easier to hit him).]]

!!''VideoGame/RockmanNoConstancy''
* Crash Man is much more frustrating than his vanilla counterpart. He moves around much more quickly and his Crash Bomber has been replaced by the Rumbling Bang. Not only is he much more accurate with the bomb itself, but its explosion covers the entire floor, making the only way to avoid it a very well-timed leap. He also gains the ability to randomly turn both invisible and invulnerable, making it very easy to be on the receiving end of a sudden ambush every time you try to attack him. Even his weakness, [[Franchise/JoJosBizarreAdventure The World]], doesn't have enough energy to kill him from a full bar, still leaving him with a fighting chance at 4 HP left.
* Wood Man. His Ice Circle moves much slower than the Leaf Shield (enough to ruin any attempt to jump over it), and the four other snowflakes (leaves) move insanely fast. It's practically impossible to defeat him without the Delay Flame, so don't bother trying. It doesn't help that he gives you the [[ScrappyWeapon the worst weapon in the entire game]] upon defeat.
* Flash Man stops time more frequently than he did in Mega Man 2, and fires a very fast projectile each time stop. The projectile's direction is random each shot, most likely hitting you, and dealing a ton of damage in the process.
* This hack's Picopico-kun is a very, ''very'' nasty one at that. The room is now a room with two conveyor belts, and the boss forms very close to you each time it does form. It's also extremely fast, and its weakness, Rumbling Bang, has to be used so that the explosions, not the bomb itself, hit Picopico-kun.
* The Boobeam Trap may be worse than it was in ''Mega Man 2''. Much like other hacks, the room layout is different, but in this case, there's three of them on both sides. Although the walls protecting the turrets can now be destroyed with just the Buster, their shots are deadlier and are ''much'' faster. Worse, their weakness is a fully-charged shot from Proto Charge, but being that it's a charge weapon, the shots from the Boobeam Trap can cancel it out.

!!''VideoGame/Rockman4MinusInfinity''
* Three of the eight Robot Masters have especially [[TakeALevelInBadass taken a level in badass]]:
** Toad Man's movements are now erratic and rapid, constantly bouncing off the walls and towards you at even the slightest movements, making him harder to hit and making you easier to hit, only worsening [[TurnsRed when his health reaches critical levels]]. To make matters worse, his Rain Flush has been replaced with Toad Spell: not only is he completely invincible while casting it, but if it connects, [[BalefulPolymorph you'll be turned into a helpless toad]], removing your ability to jump or shoot and increasing the damage you take, with the only remedy being to get hit by the spell again.
** Dust Man can heal himself with your attacks except Toad Spell while he [[WeaponsThatSuck sucks in his debris]], and can also spit out plenty of harmful chunks in a random pattern as well as Dust Crusher blocks that explode randomly as well. If he sucks you up, he incapacitates you by turning you into an [[VisualPun R-Tank]]. Mash the buttons quickly or he will give you a OneHitKill by booting you into the incinerator. Don't try to use [[OneHitKill Rush Cannon]] on him either - if he sucks it in and spits it back out at you, you're history.
** Skull Man essentially becomes a LightningBruiser here. He spends most of his time using Hell Wheel, which he can use to bounce off ramps and climb up the walls. The only good time to hit him is when he uses his buster, but the problem here is that he barely uses it, as Hell Wheel is used more often by him. While you could use Water Cutter to rip through his MercyInvincibility or Recycle Inhaler to one-shot him, he's so fast when he uses Hell Wheel that you can barely beat him with those.
* Snatch Man, the boss of Wily 2, is a MirrorBoss cranked UpToEleven. The first phase is already pretty hectic, as he's a ShadowArchetype of Mega Man that mainly just flails around the room while occasionally firing or sliding at you. (Interestingly enough, coming into contact with him will do CollisionDamage to the both of you.) However, the second phase is when things shake up rapidly: the moment it starts, he'll fly up to the ceiling out of range, at which point you have to choose four out of your eight weapons to give to him. Not only will he gladly unleash them upon you at full force, but you don't get them back until you [[BossRush re-beat the boss they belong to]] in [[MarathonLevel Wily 3]].[[note]]This also means that if you [[GuideDangIt unknowingly]] give him Toad Spell, [[PermanentlyMissableContent you won't be able to get a perfect Hero Score of 100]], as one of the secret requirements for it is using Toad Spell on Toad Man to turn him into a Toad and win the fight without killing him.[[/note]]
* The hack's version of the Wily Capsule, the Optical Capsule. Like most Capsule battles, it appears in many different spots on the screen for brief time periods to fire difficult projectile patterns. The Optical Capsule, however, is a full-on BulletHell boss that fires many, many, ''many'' lasers in a myriad of different patterns (describing them all here would only result in a WallOfText) in a random order. When [[TurnsRed it gets to 25% health]], [[DesperationAttack it unleashes everything it has at you while chaotically bouncing around the screen]]. Your one saving grace is that every time you take damage, all of its lasers that are on-screen will disappear to give you some breathing room. This isn't the case on Hard Mode, however...

!!Other
* ''Rockman 6 Unique Harassment'' is a hard hack, but its magnum opus of difficulty is the (unnamed) boss of Wily 1. This boss is essentially a hybrid of two widely reviled bosses from the Classic series: King Plane from ''VideoGame/MegaManAndBass'' and many different Devil bosses across the series[[note]]the Yellow Devil from the first ''VideoGame/MegaMan1'', Yellow Devil Mk. II from ''VideoGame/MegaMan3'', Dark Moon from ''VideoGame/MegaManV'', and Block Devil from ''VideoGame/MegaMan10''[[/note]], combining precariously jumping on small platforms over a BottomlessPit in an AutoscrollingLevel with the hectic dodging of Devil pieces. Even as its health goes down, the pieces go from moving straight forward to flying in downward arcs and even bouncing across the abyss. Once its first phase is down, it gains a massive homing projectile and can charge across the screen when fully formed. Its weakness is Tomahawk Assist, but it can only be hit so many times per pass, and using its secondary function to save yourself from the pit below if you fall in drains the weapon energy you need to actually attack it. This boss was so despised that when the 1.1 update dropped, which added many AntiFrustrationFeatures to address the complaints about the hack's high difficulty, this was the only boss (aside from the 8 Robot Masters) that [[MercyMode gives you infinite lives until it's beaten]].
[[/folder]]

* The Karumuna Bash trio, three doglike Reaverbots in the Sub-gate of the Clozer Wood. Those things are ''nasty'' if you're not CrazyPrepared for them. They all attack you at once and they are FAST. Their primary attack is jumping at you, which knocks Mega Man down and is possibly also a CameraScrew if you land right. Their other attack is to ''breathe fire'', which instantly depletes your life meter's shield so you can take MORE damage from their jump attack.

!!''Mega Man Battle Network''

!!''VideoGame/MegaManBattleNetwork 2''

!!''Mega Man Battle Network 3''

* [=BubbleMan=].EXE never leaves the back row; and the center tile on his side is a hole that generates an infinite number of bubbles, which block shots and home in on you. Popping them will just make them spawn again, and may distract the player from [=BubbleMan=]'s other attacks. And that's not even taking into account [=BubbleMan v3=], who can only be fought if you have less than 1/4 of your max HP remaining.

!!''Mega Man Battle Network 4''

* Duo gets less fondly remembered compared to the other final bosses of the series, despite being largely on par with the other series final bosses. What makes his fight less favorable is how ''early'' it shows up compared to the other entries -- Counting postgame and all, Duo's first fight is in the first third of the game, compared to the other final bosses being fought around the two-thirds or three-quarters mark. This meant you had to make do with first-tier chips, and the Battlechip and Program Advance library in the fourth game was quite lackluster, just to make things more difficult. To rub it in, his back two columns are always empty, invalidating any chips that depend on striking a panel to do damage and further reducing the number of options the player has. Duo's fight feels more fair on subsequent playthroughs when the player has a more well-developed arsenal (like being able to access all six Souls), but the first round will be a pretty big hurdle to overcome.
** If you've been reliant on the PurposelyOverpowered Dark Chips to get through the game, it pulls an unannounced VideoGameCrueltyPunishment by disabling your ability to use them. Now you're left with reduced maximum HP, no Soul access, and whatever folder you had on hand to begin with. No other final boss did this.

!!''Mega Man Battle Network 5''

!!''Mega Man Battle Network 6''

* [=DrillMan.EXE=] has lower HP than most bosses, but that's compensated by the fact his drill blocks all frontal attacks. Very few chips can bypass his drill, and if the player's folder lacks chips that can damage different rows, defeating him is pretty much impossible.

* When raising your rank to earn the right to face "S", you're forced to rematch with [=BeastMan=] way before the endgame BossRush. Unlike the Alpha-tier boss rush rematches, you're up against [=BeastMan=] '''Beta''', and he moves much faster than his first encounter.

* Elec Man is [[LightningBruiser fairly quick and aggressive, and his weapon, the Thunder Beam, deals a staggering 10 damage, enough to take you out in just 3 hits]]. It doesn't help that his weakness, the Rolling Cutter, fires a somewhat slow boomerang projectile with an unorthodox firing arc, meaning you might have to risk getting close to Elec Man to hit him with it.

** Skull Man seems to have become a LightningBruiser in this game. He spends most of his time using Hell Wheel, which he can use to bounce off ramps and climb up the walls. He barely uses his buster, but that's the only good time to hit him. While you could use Water Cutter to rip through his MercyInvincibility or Recycle Inhaler to one-shot him, he's so fast when he uses Hell Wheel that you can barely beat him with those.

* ''Rockman 6 Unique Harassment'' is a hard hack, but its magnum opus of difficulty is the (unnamed) boss of Wily 1. This boss is essentially a hybrid of two widely reviled bosses from the Classic series: King Plane from ''VideoGame/MegaManAndBass'' and many different Devil bosses across the series[[note]]the Yellow Devil from the first ''VideoGame/MegaMan1'', Yellow Devil Mk. II from ''VideoGame/MegaMan3'', Dark Moon from ''VideoGame/MegaManV'', and Block Devil from ''VideoGame/MegaMan10''[[/note]], combining precariously jumping on small platforms over a BottomlessPit in an AutoscrollingLevel with the hectic dodging of Devil pieces. Even as its health goes down, the pieces go from moving straight forward to flying in downward arcs and even bouncing across the abyss. Once its first phase is down, it gains a massive homing projectile and can charge across the screen when fully formed. Its weakness is Tomahawk Assist, but it can only be hit so many times per pass, and using its secondary function to save yourself from the pit below if you fall in drains the weapon energy you need to actually attack it. This boss was so despised, when the 1.1 update dropped that added many AntiFrustrationFeatures to address the complaints about the hack's high difficulty, this was the only boss aside from the 8 Robot Masters that [[MercyMode gives you infinite lives until it's beaten]].

* Quick Man, right after his own [[ThatOneLevel hair-pulling level]]. He is incredibly fast, but can still deal a respectable 4 damage per hit both with his body and his homing spread of Quick Boomerangs. While Flash Man's Time Stopper can take half his life in one shot[[note]]"one shot" meaning its entire weapon energy supply[[/note]], the player will probably need it to get past the daunting laser barrage right before his door. This was enforced by the dev team, who initially conceived Quick Man as a rival character and thus made him extra difficult to beat, to the [[{{Pun}} point]] that the boomerang on his head sticking out of his mugshot frame on the stage select screen is meant to be indicative of his high difficulty compared to the other seven Robot Masters.

* Ring Man has a highly unorthodox pattern to his ring tosses, employing a ConfusionFu strategy to trick players into dodging into the rings due to how Ring Man jumps to catch them or jumps to toss them and catch them on the ground. Like Shadow Man, the battle requires specific maneuvers to each attack pattern and there is little room for error thanks to Ring Man dealing heavy damage, especially [[CollisionDamage from a body blow]]. Fighting them without their weakness is especially a "learn or die" experience.

* Elec Man is fairly quick and aggressive, and his weapon, the Thunder Beam, deals a staggering 10 damage, enough to take you out in just 3 hits. It doesn't help that his weakness, the Rolling Cutter, fires a somewhat slow boomerang projectile with an unorthodox firing arc, meaning you might have to risk getting close to Elec Man to hit him with it.

* Quick Man, right after his own [[ThatOneLevel hair-pulling level]]. He is incredibly fast, but can still deal a respectable 4 damage per hit both with his body and his homing spread of Quick Boomerangs. While Flash Man's Time Stopper can take half his life in one shot[[note]]"one shot" meaning its entire weapon energy supply[[/note]], the player will probably need it to get past the daunting laser barrage right before his door. This was enforced by the dev team, who initially conceived Quick Man as a rival character and thus made him extra difficult to beat, to the point that the boomerang on his head sticking out of his mugshot frame on the stage select screen is meant to be indicative of his high difficulty compared to the other seven Robot Masters.
* Wily 4's boss, the Boobeam Trap, the five turrets with blindingly fast shots from the walls heading straight for you every five seconds or so. It's one of two bosses in the Wily Castle that is only vulnerable to one weapon, the Crash Bomber, which has a maximum of seven uses, and every single one must be used to defeat both the turrets themselves and the destructible barriers protecting them. If you misuse a single shot, then [[UnwinnableByDesign you will not be able to defeat this boss]]. And since you don't get energy refills after death, you either need to take forever restocking energy off the few enemies in the pre-boss hallway or just game over entirely and restart the stage, [[ContinuingIsPainful which will strip you of all your E-Tanks]]. The only mercy you're given is that the barriers you destroy don't respawn if you die.

* Shadow Man is a difficult fight, mainly due to how much he operates on the RandomNumberGod. His pattern is that he will jump at a random height either two or three times in your direction, and then either throw two shurikens (one directly at you and one into the air at a 45° angle) or ''very'' quickly slide at you before starting again. While the shurikens take about half a second to charge up, the slide is instant, and actually does more CollisionDamage than being hit by him regularly. Although his weakness, [[PowerUpLetDown Top Spin]], can kill him in only four hits, it requires you to get very close to him (which will often get you hit, making this more of a battle of trading blows), and due to Top Spin's HitboxDissonance, it's entirely possible to accidentally use all of its energy in a single attack.

* Bright Man has two main methods of attack: jumping towards your location and shooting weak pellets either straight at you or upward/downward at slight angles. Seems simple enough, but his third attack is where problems arise. If Bright Man's at specific amounts of health, there is a chance that he will use Flash Stopper, an attack that will freeze Mega Man wherever he is on the screen for several seconds to get a free hit. Sometimes, he'll only shoot aforementioned weak pellets at you, but if you get unlucky, he'll jump right on you. This is especially bad since in ''Mega Man 4'', seven out of the eight Robot Masters do a staggering '''8''' units of CollisionDamage, about a fourth of Mega Man's health. This means that even if you're both at low health, he can easily freeze you and tackle you to steal the win. His weakness, Rain Flush, can kill him in all seven of its uses, but it has a long delay between uses, and it won't bypass the health thresholds he can use Flash Stopper at, so the fight is still not free by any means.
* Ring Man has a highly unorthodox pattern to his ring tosses, employing a ConfusionFu strategy to trick players into dodging into the rings due to how Ring Man jumps to catch them or jumps to toss them and catch them on the ground. Like Shadow Man, the battle requires specific maneuvers to each attack pattern and there is little room for error thanks to Ring Man dealing heavy damage, especially from a body blow. Fighting them without their weakness is especially a "learn or die" experience.

* Slash Man has two different attack patterns: one where you can freely shoot him because he keeps following you and trying to slash you; and one where he goes to the ceiling, drops blobs of red goop, and then randomly chooses to either dive at you from the wall or drop down and go back to one of his starting patterns. If a blob lands on your head, you'll get slowed down and lose the ability to jump, slide, or shoot; if it lands on the floor, it will create a sticky puddle that will completely immobilize you if you step in it, making you a sitting duck for Slash Man's dive and slash attacks. And just to add insult to injury, his slash attack can actually [[AttackReflector reflect your shots back at you]] if you attack at just the wrong time. It doesn't help that whenever he's hit by one of his weaknesses (Freeze Cracker or Scorch Wheel), he goes to the ceiling right after he recovers.
* Wily Capsule 7, the FinalBoss, is infamously difficult even by the standards of final bosses for the ''Mega Man'' series. His main attack is shooting four elementally charged orbs that [[{{Roboteching}} stop mid-flight to adjust their path twice]], making them extremely difficult to avoid without great amounts of precision. While tbe electric sphere isn't a huge issue as it does minor damage and has no additional status effects, the ice sphere freezes Mega Man in place, leaving him open to quick and powerful ground-traveling sparks for additional damage, and the fire sphere immobiizes Mega Man and sets him ablaze as he takes a random amount of continuous damage. His weakness, the Wild Coil, is (as per the tradition) not only difficult to hit him with, but if even one shot is missed, it won't have enough energy to defeat him. Keiji Inafune, the franchise's producer, has admiited to purposefully making this fight insanely hard, and even playtesters found this one impossible without using at least one E-Tank.

* Burner Man has a myriad of ferocious attacks - dashing back at forth at high speeds, tossing incendiary grenades, releasing paralyzing snares, a flaming dive tackle that sends shockwaves across the ground, and his Wave Burner, capable of absorbing shots and backing you into a corner while it's active. His weakness, Cold Man's Ice Wall, makes the fight much more different, as you have to use the Wall to push him into the spikes on either side of his arena. However, the Ice Wall requires you to get dangerously close to him[[note]]his arena is two screens wide, so it's easy to get surprised by a sudden ambush from off-screen[[/note]], and can be only used when he is on the ground; if you use it at any other time, he'll bust right through it, and you'll have wasted your ammo for little damage. If you mess up too many times, it's easy to run out of ammo and lives and be forced to go through his difficult stage all over again.
* Dynamo Man is a similarly brutal fight. His main attacks are dashing back and forth, deploying durable electric tendrils at three different heights, and jumping across the room while releasing five sparks in a semi-circle that dart towards the player in a random order. What really makes this battle particularly nasty are both that a lot of his attacks shield him, and his two special maneuvers. One is his Lightning Bolt, where he sends 3 orbs that orbit around him into the air and then brings down 3 fast, deadly sets of lightning strikes.[[note]]This attack can be prevented by shooting the orbs as they're circling him, but the timing is tight and they will quickly head towards the player after being shot.[[/note]] The other is when his health gets low, in which case he will sometimes randomly jump into a recharger at the top of the screen and quickly regain health unless it's destroyed in time. Even his "weakness", Copy Vision, is a pitiful stationary turret that does little damage to him and doesn't give him a special reaction, making for a very hectic and drawn-out battle.
* Halfway into King Stage 2, the game's first MarathonLevel, you'll encounter King Plane, a simultaneous PlatformBattle and AutoscrollingLevel over a BottomlessPit. The Plane not only [[InterfaceScrew does not have a visible health bar]], but will also take any opportunity to send you plummeting to your death with its two main attacks: an unavoidable screen-clearing laser that takes many shots to cancel out and can wipe out nearly a third of your health on hit, and a RocketPunch that not only homes in on your position, but will destroy any platform it connects with, easily killing you if you're unlucky. While the boss is generous enough to [[BossArenaRecovery constantly provide power-ups in bubbles during the fight]], they are mixed in with flashbangs that white out the screen for about a second, more than enough time to slip into the abyss. Its weakness as Mega Man, Spread Drill, is difficult to hit it with due to how the boss bobs up and down, and its weakness as Bass, Treble Boost, drains energy very quickly during use and has to be bought from the shop for 200 bolts beforehand. If you die, it's back to the beginning of the mini-stage that comes before it as well.

* The final battle against the Wily Machine in this game is an arduous task. It's one of three battles in the Classic series that are ''three'' phases back-to-back with no breaks in-between[[note]]the first being the Wily Machine from ''6'' and the second being the Mega Mech Shark from this game; however, the former is widely regarded as an AnticlimaxBoss, and only third and final phase of the latter is seen as overly difficult[[/note]], technically giving it the status of a MarathonBoss. It also comes directly after the traditional series BossRush, so if the player has exhausted all of their weapons' energy on the Robot Master rematches without an M-Tank to spare, things can get ugly. All three of his phases have their own problems as well: the first phase is a TennisBoss with large, bouncing eggs that take many hits to detonate and can only hurt him in a specific spot, the second phase has powerful stomping and ramming attacks as well as a flame jet that can be extremely difficult to avoid, especially at close range, and the third and final phase, the Wily Capsule 9, is a heavy user of TeleportSpam and quick, deadly projectile patterns from anywhere on the screen with a weakness to Plug Ball, a weapon that is nigh useless against airborne targets.

* Torch Man is an extremely intimidating opponent. He is a LightningBruiser, capable of unleashing ferocious fiery kicks at close range that require good reaction time to jump over, and quick flaming fist projectiles from a distance that must be jumped over or slid under depending on their height. He's not afraid to follow up either with a devastating flaming dive tackle that homes in, hits hard, and will knock you away from him. Even getting away from him isn't safe, as he will quickly hop towards you to bridge the gap if you do. To make matters worse, when he [[TurnsRed reaches half health]], he gains access to the Power Gear, which gives him a DesperationAttack where he unleashes giant flaming wheels (that are ''very'' hard to jump over) from both sides of the screen one after another and finishes it off with a giant flaming column that once again tracks your position. Although his weakness, Tundra Storm, can make quick work of him, you'll have to be close to him to use it unless you use the weapon energy-guzzling Power Gear to make it a [[SmartBomb screen-clearing weapon]], and if you used all of it to freeze the OneHitKill [[AdvancingWallOfDoom Advancing Walls Of Doom]] in his stage, you're out of luck.

* Armored Armadillo on ''Maverick Hunter X'''s Hard Mode, where he picks up an attack where he bounces off the walls ''and'' fires off bullets in four directions. Even if you use the Electric Spark to take out his armor, it's still hellish. If you're playing as Vile in ''MHX'', you ''will not'' have Peace Out Roller (the same thing as Electric Spark, except it's lobbed instead of shot) for when you fight him, because its [[TheKeyIsBehindTheLock weapon type is locked until you beat him]]! That's right, you unlock a boss's weakness by defeating that boss. To make up for this, he's also weak to the fist weapons, which you ''do'' get from Spark Mandrill; however, they don't remove his armor.
* The first boss of Sigma's Palace, the Bospider. This boss has a peculiar movement scheme[[note]]based on a popular Japanese lottery system called [[http://en.wikipedia.org/wiki/Ghost_Leg amidakuji]], or "Ghost Leg"[[/note]] - there are four poles at the center of the screen, and "bridges" appear at random between them to determine what path Bospider will take down to the floor, where it will then briefly expose its weak point (the center of its abdomen) and quickly zip back up to the ceiling to start again. The problem is that you're given a very short time to see where the bridges are laid out and determine what path it will take, and not only does Bospider get faster and faster as its health goes down, but it also occasionally showers down miniature spiders called Petitpiders that can both absorb any shots coming Bospider's way and damage you before you can shoot at it. More often than not, you'll try to get your once-per-pattern shot in only for a Petitpider to get in the way or for Bospider to slam down on you for heavy CollisionDamage, making the fight much longer and more difficult.

* Although the second encounter with Violen in the first stage of the X-Hunter Base can be tricky with his unpredictable mace ball, he pales in comparison to the boss of the following stage, the Serges Tank. The entire fight starts on four vertically moving platforms over a floor of OneHitKill spikes, and you're only given around half of the screen to fight against it - the rest is taken up by the Tank itself. Its arsenal is fierce: the first phase consists of four durable vertically-placed cannons firing fast projectiles that either go straight forward or bounce along the floor. Once they're all destroyed, Serges reveals himself... but not before [[AdvancingBossOfDoom inching forward and destroying two of the four platforms]], leaving you with ''even less'' space and footing. Serges will then start moving up and down erratically while firing projectiles that alternate between exploding into Xs or +s. To make matters worse, not only is Serges only vulnerable on his top half, but he also tends to get very close to the spikes below, so even one mistake can result in a very difficult battle having to be restarted from scratch. The only saving grace is that you can skip the first phase destroying the four cannons with a fully charged Giga Crash at the beginning, leaving Serges exposed to your attacks, but even then, good luck landing hits on him.

* While Sigma himself is very pattern-based and easy to read, the true terror appears in the form of Kaiser Sigma, his gigantic battle body. Kaiser Sigma is so large that he fills up half of the arena you fight him in, and his weak spot is [[HitboxDissonance not his head, but rather the small "fins" directly above it]]. He has two patterns, one when you're behind him and one when you're in front of him. When you're behind him, he shoots many homing missiles that hit extremely hard, and when you're in front of him, he charges and fires a cone-shaped laser either upward or downward that continuously damages and stuns you when you get hit by it. All the while he's spawning tracking bombs. Only two things can damage him: charged X-Buster shots (in a game where the X-Buster upgrade actually [[PowerUpLetDown makes it more difficult to use]]), and the [[GameBreaker Game-Breaking]] Z-Saber, which can take him down in only two hits, but get hit ''once'' while trying to slash him, and it'll be cancelled out. Even after you manage to kill him, it's not over, as you still have one last trial: wall-climbing a long vertical [[AutoscrollingLevel autoscroller]] with the Sigma Virus trying to knock you into the damaging lava below. If he successfully manages to, it's entirely possible for you to get stuck in hitstun under one of several outcroppings in the shaft, and since the lava is treated as a solid floor, you can get crushed, in which case [[ContinuingIsPainful it's back to the beginning of Sigma's first form]].

* Infinity Mijinion. To start things off, all of his attacks are entirely random, and his main gimmick is being able to create clones upon taking enough damage. The clones are not only completely identical to the real Mijinion, but they are also quite durable, usually taking several charge shots in order to kill. The clones also releases slow-moving homing blobs of goo which take several shots to kill, easily shielding Mijinion himself and flooding the screen. Whenever he's not making clones, he's firing a slow projectile that can change angles at 90°, shooting an 8-way spread, or raining down Ray Arrows at blinding speed. Even his weakness, the Guard Shell, requires a specific attack to be reflected back at him, and he'll instantly create a clone when it hits. The battle is almost a no-win situation: hit him with something too strong and he'll create a clone; hit him with something too weak and he'll be more than happy to even ''heal himself completely''.

* Unbeatable Air Man in [[spoiler:Tier X]] is a nightmare for all the wrong reasons. He starts off as a straight-up copy of Mega Man 2's Air Man fight until you knock off half his health. Then he grows giant and that's where things get problematic: he usually spawns giant tornadoes all over the field in hard-to-dodge patterns as his main attack, but he can also shoot tons of fast-moving, smaller, standard tornadoes. And to make matters worse, when you fight him during the story mode you're not playing as Mega Man, but as [[spoiler:Mario]], in a game that is decidedly ''not'' made for his gameplay. [[spoiler:Mario]]'s only safe way of attacking Air Man is with his fireballs, but when he takes enough damage he loses his [[spoiler:Fire Mario]] status and has to rely on his jumps to hurt him. And not only is jumping on Air Man already dangerous since you're making an easy target of yourself, but it barely works half the time due to the jump attack's inconsistent hit detection and will hurt [[spoiler:Mario]] instead. Funnily enough, he's much easier to fight in the True Arena because you're playing as Mega Man there, who's properly designed to fight him.

* [=ThunderMan.EXE=] returns for Red Sun, trading his three thunder clouds (detailed above) for one that circulates the perimeter of the field. This time, the thunder cloud will fire paralyzing thunder balls whenever [=MegaMan=] lines up with it horizontally or vertically, so if you stand in the wrong position it can stunlock you for a short time.

* [=CloudMan.EXE=] evidently took cues from [=BubbleMan.EXE=]. He stays in the back row, protected by clouds that periodically shoot paralyzing thunderballs. The clouds don't have much health, but despite this [[TheComputerIsACheatingBastard can take infinite punishment from time-stopping Chips.]] He can also hide in a cloud while summoning a [[AdvancingWallOfDoom pillar of clouds that chases you around]], and the pillar remains even after [=CloudMan=] stops hiding. Even in a Liberation Mission, [=CloudMan=]'s field attack is equally frustrating. Anyone hit by this attack gets ''paralyzed'' and will not be usable for the next 2 turns, thereby slowing down your progress on defeating him once you are in position to attack him directly. Even if your Defense Navi can negate the damage done by this attack, it won't negate the paralysis.

* [=DrillMan.EXE=] makes the game a nightmare. He has lower HP than most bosses, but that's because frontal attacks have no effect -- his drill is always blocking frontal attacks, so you have to go ''around'' the drill with [=WideSwords=] and such. Only a handful of chips can bypass his drill, so good luck having one in advance when he appears!
* [=DrillMan.EXE=]'s ''younger brother'' [=BubbleMan=].EXE is much more annoying, despite being fought earlier in the game and theoretically being easier. To elaborate, he never leaves the back row and the center tile on his side is a hole from which spout an infinite number of bubbles, which block shots and home in on you, always moving into your row so as to block your line of fire at [=BubbleMan=]. Since they're limited by number on screen, if you stand there shooting them, they'll just spawn faster. Meanwhile [=BubbleMan=] is using his ''own'' attacks on poor distracted [=MegaMan=]. And that's not even taking into account [=BubbleMan v3=], who almost ascends to GoddamnedBoss status. You can't even ''find'' him unless [[spoiler:you have less than 1/4 of your max HP.]] Frickin' bastard.
* [=KingMan.EXE=] is the second hardest boss. He hides in the far back row while his nearly invincible, regenerating chess pieces attack you and block your spaces, which means no [=AreaGrab=] or powerful direct and melee attacks. If that wasn't annoying enough, if you stay in the back row (the easiest way to avoid his chess pieces), [=KingMan=] has a "plan B" attack, where he summons some new chess pieces and ''permanently steals an entire row of your area''. Not even Bass' auras can compare to this guy's cheapness. But it's okay, break-type chips can destroy his chess pieces...just kidding, the chess pieces are only incapacitated temporarily. If you figure this out and try it, he'll use a different and more vicious set against you.

* Armored Armadillo on ''Maverick Hunter X'''s Hard Mode, where he picks up an attack where he bounces off the walls ''and'' fires off bullets in four directions. Even if you use the Electric Spark to take out his armor, it's still hellish.
** If you're playing as Vile in ''MHX'', you ''will not'' have Peace Out Roller (the same thing as Electric Spark, except it's lobbed instead of shot) for when you fight him, because its [[TheKeyIsBehindTheLock weapon type is locked until you beat him]]! That's right, you unlock a boss's weakness by defeating that boss. To make up for this, he's also weak to the fist weapons, which you ''do'' get from Spark Mandrill; however, they don't remove his armor.

* [[OneWingedAngel Wolf Sigma]], the FinalBoss. The first time you fight him, you might be surprised by the sheer increase in difficulty from his previous form that can be easily locked into an exploitable pattern. Only two weapons, fully charged X-Buster shots and Rolling Shield, do damage to his weak point, the sides of his head, which can only be reached via his claws or with extremely careful [[WallJump Wall Jumps]]. Even then, both are rather weak and unwieldly, as the X-Buster takes a few seconds to charge (uncharged shots will bounce off) and only does 1 damage, and although Rolling Shield does 2, it obeys gravity, giving it a very awkward firing arc, and it still takes ''16'' shots with it to bring him down. He has four different attacks that are not only entirely random as to when they occur, but also extremely strong, as even with all 8 health-extending Heart Tanks as well as the PowerArmor that reduces all damage you take by 50%, he can still easily kill X in as little as 4 hits. All of this makes for a very hectic and stressful last fight. He was made slightly easier in ''[[VideoGameRemake Maverick Hunter X]]'' by letting the [[Franchise/StreetFighter Hadouken]] [[OneHitKill take him down instantly]], and you can use the X-Buster while using the charged Rolling Shield, but this takes a lot of skill in order to pull off, since you need full health to use the Hadouken.

** Amusingly, by the time you get to face him again in the third game, there are several upgrades available (ie, Shadow Dash) that render him a pushover.
* Then the Rainbow Devil shows up. It's just as cheap as previous models. It has an especially annoying attack where it bounces around the room, splits into two parts, then into four before finally reforming. It also has a punch attack that crosses nearly half the arena and a projectile attack that makes nearly the entire ground a danger zone. Good times. Thankfully, the redux in ''Zero 2'' is actually somewhat easier.

** He's an Expy of M. Bison, which helps explain his difficulty (of course). That huge fireball he "shoots" after dodging backwards is the Psycho Crusher.

* Chronoforce on Expert starts the fight with Time Bomb, and it never wears off, so he's always in turbo speed. What's more, you know that spreading icicle move he does that you were able to jump between on Normal? Now he shoots two sets of icicles, the second set covering all the angles the first doesn't, making a roughly 90-degree arc that's really tough to avoid whether you try jumping between them or dashing underneath Chronoforce to get past them entirely. And may God help you if you haven't figured out the trick to dodging his attack where he shoots a whole volley of exploding icicles at you from the background, then rewinds them to un-explode and hit you again.
** Even worse? He uses Time Bomb ''again'' right before he uses that attack. The good thing? The ones used at the start of those attacks can actually wear off (only after he's done with the attack, of course) and he only uses it twice, once at slightly beneath half health and the other about two charged shots before death.

* [=QuickMan.EXE=]. The name alone should key you in to how annoying he's going to be. He is invincible at all times except when moving or attacking, moves like a spastic monkey on crack so that his vulnerability then doesn't even matter, and his attacks are irritating to dodge, because [[ShapedLikeItself Quick Boomerangs are really, REALLY fast moving]]. It doesn't help that he's the second boss of the game, the first boss was a complete chump, and the next boss AFTER him isn't exactly threatening either, so he's not even really a WakeUpCallBoss... Worse yet, it's ''entirely'' possible for the game to be UnwinnableByMistake here, as you can't leave his area (either to recover HP or improve your moveset) once you enter (but nothing stops saving...)

** What makes these two fights especially annoying that Bass has an Aura that can only be removed temporarily using an attack with over 100 power (permanently with a near-impossible to obtain chip), while Alpha has a shield that requires multiple consecutive hits to remove. Hope you brought a deck with both high damage ''and'' rapid firing chips!
*** Though Bass is somewhat easier compared to [=BubbleMan=], [=DrillMan=], and [=KingMan=]. Breaking chips are not common until ''4'', and those chips would help a lot against those three. Bass has no such resistance; Life Aura can be chipped away by any strong chip or North Wind (blows auras away).

* Duo's Meteo Fist attack can easily make the fight unwinnable if you don't have Air Shoes or a Panel Return handy, since your field is cracked to the point where you can't dodge anything.
** That's not the only way the fight against Duo can become unwinnable. Thanks to the game's NewGamePlus structure, you'll fight Duo in a "normal" playthrough with more-or-less the chips you'd get in the first third of one of the other games, and when you fight him on a NewGamePlus, he'll have his health scaled up to truly ridiculous levels. A MarathonBoss is fine for a final boss normally, but problematic in the Battle Network series because no matter how long the battle lasts, you can ''only'' draw thirty chips. If you don't pack your folder with thirty of the most damaging chips/combos in your library (and then consistently hit with them, as they likely won't be the easiest to connect with), or throw too much defense in your folder, you will ''run out of attacks'' before he runs out of health. For the third fight, you pretty much need a top-tier combo folder out of a strategy guide just to deal enough damage, never mind actually ''fighting'' him with it. Oh, and if you're relying on drawing just the right combo in the same hand, for a PA or a powered-up megachip, you'll have to fight another boss right before him every time you get unlucky. Or miss. In addition, Duo can only be hit when the light on his chest is glowing.
** Duo's battle terrain also turns his 2 back columns completely empty, meaning panel-reliant chips like the [[GameBreaker game-breaking]] Air Hockey are ineffective.

* [=CloudMan.EXE=] evidently took cues from [=BubbleMan.EXE=]. He stays in the back row, protected by clouds that periodically shoot paralyzing thunderballs. The clouds don't have much health, but despite this [[TheComputerIsACheatingBastard can take infinite punishment from time-stopping Chips.]] He can also hide in a cloud while summoning a [[AdvancingWallOfDoom pillar of clouds that chases you around]], and the pillar remains even after [=CloudMan=] stops hiding.
** Even in a Liberation Mission, [=CloudMan=]'s field attack is equally frustrating. Anyone hit by this attack gets ''paralyzed'' and will not be usable for the next 2 turns, thereby slowing down your progress on defeating him once you are in position to attack him directly. Even if your Defense Navi can negate the damage done by this attack, it won't negate the paralysis.
* Nebula Gray. It has a huge repertoire of devastating moves; it has one that, like Duo's Meteo Fist, can leave your entire side of the field broken, another that ''drains your HP and restores its own'', plus it also has a passive attack just to keep you on your toes. It can only be damaged by hitting the blue flame that orbits it, making it entirely possible to line up an attack and then miss. It also can summon Dark [=MegaMan=] to use some attacks of its own on you, which can potentially do ridiculous damage should it hit a Soul's weakness. Not to mention one of them stuns you, making it that much easier for the other attacks to hit you. Fun! And just like Duo, Nebula Gray's 2 back columns are completely empty, forcing the player to adjust their strategy if their previous tactics used panel-reliant attacks.

* Halfway into King Stage 2, the game's first MarathonLevel, you'll encounter King Plane, a simultaneous boss and AutoscrollingLevel, taking place on many small platforms over a BottomlessPit. The Plane will take any opportunity to send you plummeting to your death with its two main attacks: an unavoidable screen-clearing laser that takes many shots to cancel out and can wipe out nearly a third of your health on hit, and a RocketPunch that not only homes in on your position, but will destroy any platform it connects with, easily killing you if you're unlucky. While the boss is generous enough to constantly provide power-ups in bubbles during the fight, they are mixed in with flashbangs that white out the screen for about a second, more than enough time to slip into the abyss. Its weakness as Mega Man, Spread Drill, is difficult to hit it with due to how the boss bobs up and down, and its weakness as Bass, Treble Boost, drains energy very quickly during use and has to be bought from the shop for 200 bolts beforehand. If you die, it's back to the beginning of the mini-stage that comes before it as well.

* [[OneWingedAngel Wolf Sigma]], the FinalBoss. The first time you fight him, you might be surprised by the sheer increase in difficulty from his previous form that can be easily locked into an exploitable pattern. Only two weapons, fully charged X-Buster shots and Rolling Shield, do damage to his weak point, the sides of his head, which can only be reached via his claws or with extremely careful [[WallJump Wall Jumps]]. Even then, both are rather weak and unwieldly, as the X-Buster takes a few seconds to charge (uncharged shots will bounce off) and only does 1 damage, and although Rolling Shield does 2, it obeys gravity, giving it a very awkward firing arc, and it still takes ''16'' shots with it to bring him down. He has four different attacks that are not only entirely random as to when they occur, but also extremely strong, as even with all 8 health-extending Heart Tanks as well as the PowerArmor that reduces all damage you take by 50%, he can still easily kill X in as little as 4 hits. All of this makes for a very hectic and stressful last fight. He was made slightly easier in [[VideoGameRemake Maverick Hunter X]] by letting the [[Franchise/StreetFighter Hadouken]] [[OneHitKill take him down instantly]], and you can use the X-Buster while using the charged Rolling Shield, but this takes a lot of skill in order to pull off, since you need full health to use the Hadouken.

* The fight with Gate is a TennisBoss on many small platforms over a BottomlessPit while he constantly gives chase and occasionally[[note]]often to the point of making the fight excessively long[[/note]] fires off random colored "gates" that have various detrimental effects[[note]]red ones slow you down, orange ones fire at you, green ones home in, blue ones have a vacuum effect, and purple ones generate [[DemonicSpiders Nightmare Viruses]][[/note]]. The only way to damage him is to attack the "gates" so they split into smaller projectiles that can hit him, but they can also damage ''you'', so you'll often find the both of you taking damage simultaneously. The red and blue "gates" are by far the most dangerous, as they greatly increase your chances of falling into the pit or getting knocked in. When he gets below half health, he gains an additional attack: ''breaking the platforms that you need to stand on to survive''. Not only can it easily kill you, but it also doesn't allow you to hit him in return. This fight is tedious, dangerous, and overall very frustrating.

* The Boobeam Trap is far worse than it was in Mega Man 2. Much like other hacks, the room layout is different, but in this case, there's three of them on both sides. Their shots are deadlier and are ''much'' faster. Worse, their weakness is a fully-charged shot from Proto Charge, but being that it's a charge weapon, the shots from the Boobeam Trap can cancel it out.

* Toad Man and Dust Man have [[TakeALevelInBadass taken a level in badass]].
** Toad Man's movements are now erratic and rapid. He'll jump if you try to shoot him or get close to him. Watch out if he hits you with his rain attack.
** Dust Man can heal himself with your attacks except Toad Spell when he [[WeaponsThatSuck sucks in his debris]]. If he sucks you up, he turns you into an E-Tank. Mash the buttons quickly or he will give you a OneHitKill by booting you into the incinerator.
* Skull Man seems to have become a LightningBruiser in this game. He spends most of his time using Hell Wheel, which he can use to bounce off ramps and climb up the walls. He barely uses his buster, but that's the only good time to hit him. While you could use Water Cutter to rip through his MercyInvincibility or Recycle Inhaler to one-shot him, he's so fast when he uses Hell Wheel that you can barely beat him with those.
* The hack's version of the Wily Capsule, the Optical Capsule. Like most Capsule battles, it appears in many different spots on the screen for brief time periods to fire difficult projectile patterns. The Optical Capsule, however, is a full-on BulletHell boss that fires many, many, many lasers in a myriad of different patterns in a random order. When it gets to 25% health, it unleashes everything it has at you while chaotically bouncing around the screen. Your one saving grace is that every time you take damage, all of its lasers that are on-screen will disappear to give you some breathing room. This isn't the case on Hard Mode, however...

* ''Rockman 6 Unique Harassment'' is a hard hack, but its magnum opus of difficulty is the (unnamed) boss of Wily 1. This boss is essentially a hybrid of two widely reviled bosses from the Classic series: King Plane from ''VideoGame/MegaManAndBass'' and many different Devil bosses across the series[[note]]the Yellow Devil from the first ''VideoGame/MegaMan1'', Yellow Devil Mk. II from ''VideoGame/MegaMan3'', Dark Moon from ''VideoGame/MegaManV'', and Block Devil from ''VideoGame/MegaMan10''[[/note]], combining precariously jumping on small platforms over a BottomlessPit in an AutoscrollingLevel with the hectic dodging of Devil pieces. Even as its health goes down, the pieces go from moving straight forward to flying in downward arcs and even bouncing across the abyss. Once its first phase is down, it gains a massive homing projectile and can charge across the screen when fully formed. Its weakness is Tomahawk Assist, but it can only be hit so many times per pass, and using its secondary function to save yourself from the pit below if you fall in drains the weapon energy you need to actually attack it. This boss was so despised, when the 1.1 update dropped that added many AntiFrustrationFeatures to address the complaints about the hack's high difficulty, this was the only boss aside from the 8 Robot Masters that gives you infinite lives until it's beaten.

* Quick Man is a default devkit boss for the MaGMML series from this game onward, but the devs toned him down a little bit by fixing the AI issues that caused him to break from his tough but learnable attack pattern and devolve into an unpredictable, spastic mess in ''MM2''. However, his boss fight in the level ''Breaking Ground'' is still insanely hard for different reasons: his boss fight takes place on rows upon rows of destructible Chill Man blocks, and ''any'' movement whether it's walking, jumping, or blasting will break them and mess with the elevation. This completely ruins the flow of the battle making it fiendishly hard to safely hit Quick Man while he zips and leaps around all over the place while he puts the hurt on you. The fight can ''really'' drag on, and if you run out of blocks for footing, you get dropped into a pit infested with enemies that will kill you in seconds.

* Unbeatable Air Man in [[spoiler:Tier X]] is a nightmare for all the wrong reasons. He starts off as a straight-up copy of Mega Man 2's Air Man fight until you deplete half his health, until you knock off half his health. Then he grows giant and that's where things get problematic: he usually spawns giant tornadoes all over the field in hard-to-dodge patterns as his main attack, but he can also shoot tons of fast-moving, smaller, standard tornadoes. And to make matters worse, when you fight him during the story mode you're not playing as Mega Man, but as [[spoiler:Mario]], in a game that is decidedly ''not'' made for his gameplay. [[spoiler:Mario's only safe way of attacking Air Man is with his fireballs, but when he takes enough damage he loses his [[spoiler:Fire Mario]] status and has to rely on his jumps to hurt him. And not only is jumping on Air Man already dangerous since you're making an easy target of yourself, but it barely works half the time due to the jump attack's inconsistent hit detection. Funnily enough, he's much easier to fight in the True Arena because you're playing as Mega Man there, who's properly designed to fight him.

* The three bosses of the [[ThatOneLevel notorious]] Yggdrasil level are just as fiendishly difficult as the stage itself for all the wrong reasons: unnecessarily huge health pools, unpredictable AI, and outright unfair attacks. It's worth noting that in a game with more than it's fair share of difficult bosses, they're among the few ''outright excluded from the arena challenges'' due to being so ridiculously annoying to fight.
** Crator is considered to be the toughest of the three by far. He spends a lot of time deflecting your shots, is incredibly aggressive and prone to getting in your face, and has attacks that lop off around half your health at best or one-hit kill you at worst. Even his weakest attack, a series of energy bursts shooting up from the ground, makes up for its lacking strength by coming out fast and being incredibly hard to dodge. To make things worse, his weakness to the Slash Claw does little to mitigate the difficulty of his fight since its lack of range means you have to constantly put yourself in danger of being slaughtered to use it.
** Cream is no slouch either, since she has an instant death attack of her own that comes out way too fast for its own good, loves to jump around the arena like a spastic monkey, and has a ton of projectile attacks that can be hard to dodge since she has no tells indicating what she'll be firing at you.
** And while not as bad as the above two, Kichona is annoying to fight all the same due to not only possessing a whopping two health bars, but also being able to restore her health with her syringe attack. She can also randomly glitch her way out of the fight and make it flat-out unwinnable.

* The Tier 2 boss is Dagger Man, who is every bit as hard as he was in ''Super Fighting Robot''. He loves to teleport all over the place and can easily telefrag you for cheap collision damage, his cutting waves come out fast with little to no warning, and his nastiest attack is him shooting daggers to the floor and creating shockwaves like in his game of origin, only at a far greater rate. It's ''incredibly'' hard to keep up with all the daggers and shockwaves, and he loves to spam it.

** Crator is considered to be the toughest of the three by far. He spends a lot of time deflecting your shots, is incredibly aggressive and prone to getting in your face, and has attacks that lop off around half your health at best or one-hit kill you at worst. Even his weakest attack, a series of energy bursts shooting up from the ground, makes up for it's lacking strength by coming out fast and being incredibly hard to dodge. To make things worse, his weakness to the Slash Claw does little to mitigate the difficulty of his fight since its lack of range means you have to constantly put yourself in danger of being effortlessly slaughtered to use it.
** Cream is no slouch either, since she has an instant death attack of her own that comes out way too fast for its own good, and loves to jump around the arena like a spastic monkey, and has a ton of projectile attacks that can be hard to dodge since she has no tells indicating what she'll be firing at you.

* Regardless of which set of Fusion Masters you fight, once you beat all four your next stop is Death Man. He's not a very complex boss but he makes up for it by doing ''absurd'' damage with his attacks, which kill from full health in just three hits!

* Although the second encounter with Violen in the first stage of the X-Hunter Base can be tricky with his unpredictable mace ball, he pales in comparison to the boss of the following stage, the Serges Tank. The entire fight starts on four vertically moving platforms over a floor of OneHitKill spikes, and you're only given around half of the screen to fight against it - the rest is taken up by the Tank itself. Its arsenal is fierce: the first phase consists of four durable vertically-placed cannons firing fast projectiles that either go straight forward or bounce along the floor. Once they're all destroyed, Serges reveals himself... but not before [[AdvancingBossOfDoom inching forward and destroying two of the four platforms]], leaving you with ''even less'' space and footing. Serges will then start moving up and down erratically while firing projectiles that alternate between exploding into Xs or +s. To make matters worse, not only is Serges only vulnerable on his top half, but he also tends to get very close to the spikes below, so even one mistake can result in a very difficult battle having to be restarted from scratch.

* Cubit Foxtar. He's able to fire her fireballs in several intricate ways, and especially if you hit him with a lightning attack, he'll transform into 5 "ghost flames" that will then fly around the screen in a pattern that requires you to time your dashes; he's invulnerable when he does this.

* Ring Man has a highly unorthodox pattern to their ring tosses, employing a ConfusionFu strategy to trick players into dodging into the rings due to how Ring Man jumps to catch some of them. Like Shadow Man, the battle requires specific maneuvers to each attack pattern and there is little room for error thanks to Ring Man dealing heavy damage, especially from a body blow. Fighting them without their weakness is especially a "learn or die" experience.