History VideoGame / TheBindingOfIsaac

* GainaxEnding: Given the general ambiguity surrounding the story, most ending cutscenes are very abstract and confusing beyond the intro and initial ending. There's also a few gag endings, mainly the ones gotten from opening the treasure chest at the end of The Womb.

** ''Afterbirth+'' has the Plan C item, which inflicts massive damage (it's enough to kill the TrueFinalBoss 100 times over) on all enemies in the room, and then kills you after three seconds. If you use it on (almost) any boss on their last lifebar, it still counts as a victory… but if you have no extra lives, it'll still end your run unless you can get into the end-of-run chest within those 3 seconds.

** There's a [[ComicBook/{{Magneto}} "Magneto"]] powerup which attracts powerups even through rocks and over gaps. Broken Magnet trinket works the same but only affects coins.

** For actively used items, boomerang and jawbone can be used to attract pickups.

** Most expansions add a lot of incredibly powerful new items and effects that would be extremely abusive on earlier version of the game, such as combining the effects of two previous useful items into one. You'll need every one of them if you want a chance to survive the horrors you'll find in the new content.

* ReligiousHorror: All throughout the game; the game starts with a fanatical mother hearing voices she thinks are from God, and continues with the titular Isaac fighting off various monsters demons, and other horrors inspired from Jewish and Christian myth and legend (mostly but not only Literature/TheBible).
* ReviveKillsZombie: [[spoiler:The Bible]], while normally dealing no damage, kills Mom [[spoiler:and Mom's Heart]] instantly. Inverted with [[spoiler:Satan, using the Bible will instantly kill you instead]].

* SegmentedSerpent Larry Jr. and the Hollow are made of multiple segments, each of which can be individually damaged. They can split into multiple entities if a segment is broken and there are two or more remaining segments on either side.

** While revival items except for Lazarus' typically revive characters in the previous room, [[spoiler:you're revived on the spot if you die during the Ultra Harbrigners/Beast fight]].

** The Tick, a randomly spawning trinket that makes bosses start out at anywhere from 5% to 15% less health from full, is fairly useful. What makes it bad is that it latches onto you and can't be removed by anything except for picking up the Match Stick trinket (which isn't always guaranteed to appear), making the negatives of it far outweigh the positives, and since the [[spoiler:the Polaroid trinket is needed to reach The Chest]], picking the Tick up by accident when you can't find or buy Mom's Purse basically makes it impossible to reach the final level on that run. Luckily, ''Rebirth'' turns the Polaroid and its new counterpart the Negative into permanent powerups, allowing the Tick and the Photos to exist in harmony. It even buffs the Tick with a health-recovering effect, and later expansions let it be removing by trinket-consuming effects.
** Despite being considered by the game as an upgrade, Shot Speed is generally mixed in reputation, being regarded as a negative in the Flash game and as a mixed benefit in ''Rebirth''. They make it easier to hit enemies and knock them away, but harder to lead shots to hit at diagonals, and knocking back enemies can be detrimental at times. High shot speed is great for some setups, but poor with items like homing tears (tears have a limited turning radius; the slower the tears are, the sharper the turns they can make) and Lump of Coal (tears get stronger the longer they're in the air, so faster tears won't gain as big a damage bonus because they'll hit the target sooner). Most items that come with shot speed upgrades are taken moreso for their other effects.

** The Dead Cat item. You get eight extra lives, but you also have your health bar reduced to one heart (and any health bar increases you find vanish on respawn), and if you die you respawn outside (with your secondary item still used up if you used it and any Soul Hearts still gone) and enemies fully healed. Good luck beating any bosses you couldn't kill on the first try, and those eight extra lives are going to need to last you the entire rest of the game. The main reason to pick it up isn't for the lives, but for the low-health benefits and contribution to the Guppy transformation

** it's possible to deliberately lose to manual actions such as donating all your health to the Blood Donation machines or [[https://youtu.be/ZDrFmzLKStI?t=3660 using the Razor Blade too much]].

** ''Afterbirth+'' has the Plan C item, which inflicts massive damage (it's enough to kill the TrueFinalBoss 100 times over) on all enemies in the room, and then kills you after three seconds. If you use it on (almost) any boss on their last lifebar, it still counts as a victory.

* MarathonBoss:
** If your damage output doesn't scale as you progress through the game, later bosses can take an obscene amount of effort to kill. This is especially true of [[spoiler:Isaac]] and [[spoiler:???]]. However, those two pale in comparison to [[spoiler:Mega Satan]] of ''Rebirth'', who takes forever without the Chaos Card due to being a BossRush as well as a regular boss with [[SequentialBoss two phases]].
** ''Afterbirth'' adds in [[spoiler:Hush]] and [[spoiler:Ultra Greed]], who not only have massive HP pools on par with [[spoiler:Mega Satan]], they are unique in that they have a DamageReduction mechanic that scales with your damage output, so you won't wind up with a combo that can kill them in twenty seconds. No matter how well-prepared you are, expect to spend a lot of time killing them.
** ''Afterbirth+'' adds [[spoiler:Delirium]], which doesn't make as effective use of the DamageReduction mechanic as [[spoiler:Hush]] and [[spoiler:Ultra Greed]] due to a quirk of [[VoluntaryShapeshifting its own battle gimmick]], but its health pool is ''even more'' stupidly massive.
** ''Repentance'' adds the DamageReduction mechanic to [[spoiler:Mega Satan]] and its own [[TrueFinalBoss alternative endgame superbosses]], [[spoiler:Mother]], [[spoiler:Dogma, Ultra Famine, Ultra Pestilence, Ultra War, Ultra Death, and The Beast]]. Oh, and [[spoiler:The Beast by itself has as much health as Delirium, ''doesn't'' sabotage its own DamageReduction, and is the final enemy in a ''very long'' BossBonanza — Dogma, the Ultra Harbingers, and the Beast are all battled one after another. The Home battles are going to take you a ''long'' time]].
** To provide hard HP numbers for all of the bosses we mentioned (and a couple that we didn't), as well as describe some gimmicks that drag these fights out even longer:[[note]]Bear in mind that your baseline damage output in this game is 3.5 per tear, so even the smallest of these numbers are going to take a while for weaker builds to reduce to 0.[[/note]]
*** [[spoiler:The "light path" Chapter 5 and 6 bosses, Isaac and ???/Blue Baby, have 2,000 HP each, and while they each have three phases, all three phases share the same life bar. The latter was the definitive TrueFinalBoss of the Flash version of ''The Binding of Isaac'' with the ''Wrath of the Lamb'' expansion. Both start out immobile, and they remain that way for the entire fight in the Flash version, but in ''Rebirth'', they start moving around in their third phases, as well as periodically teleporting around. Isaac tends to try to avoid your attacks, even periodically teleporting out of the room entirely to carpet-bomb most of the BossRoom with light beams. ??? fights more recklessly, electing to chase you down to shoot you point-blank or even attempt to TeleFrag you, but makes up for his tendency to put himself in harm's way by deploying both a ring of Eternal Flies and a steady stream of flunkies to block your shots and distract you.]]
*** [[spoiler:The "dark path" Chapter 5 and 6 bosses, Satan and The Lamb, are less straightforward. Satan himself (who was the TrueFinalBoss of Flash ''Isaac''[='=]s Halloween update]]) has only 1,200 HP, split across two phases[[note]]yes, in this case, that means that each phase has its own life bar, so using [[OneHitKill a Chaos Card or Plan C]] on the first phase will just start phase 2 rather than automatically winning the fight[[/note]]; this is more than Mom's Heart/It Lives! (which has 1,000 HP), but still would be not quite enough to qualify as a MarathonBoss in this game if not for the fact that you need to go a round with The Fallen [[SequentialBoss immediately before Satan fights you]][[note]]and, yes, using a Chaos Card or Plan C on The Fallen just one-shots The Fallen while leaving Satan himself unharmed[[/note]]. Satan's first phase drifts back and forth across the top of the room, while the second phase uses a variation of [[DiscOneFinalBoss Mom's]] attack strategy, with the main body of the boss being unseen and un-attackable and the battle consisting of the player attacking the boss's limbs (specifically his feet) that rapidly burst into the arena to attack, then retreat after a moment. The Lamb has 2,600 HP (which used to be 2,000 before being buffed in a patch), divided in a single life bar across two phases[[note]]yes, this means that you ''can'' one-shot The Lamb immediately and be done with the fight right away with a Chaos Card or Plan C[[/note]], and unlike Isaac and ???, it actively pursues the player throughout the entire fight. "Division" is taken literally in the second phase, as The Lamb [[DetachmentCombat splits itself into two entities]], [[DualBoss its head and its body]], both of which have half of the remaining life meter and must be defeated to win the battle. The body is immobile but [[BlackoutBasement briefly darkens the room when killed]], while the head retains the mobility of the first phase and adds a DashAttack. We didn't mention either of these earlier because Satan's HP still isn't as impressive as Isaac or Blue Baby's even with The Fallen as a cushion[[note]]even though Satan can't be cheesed with a OneHitKill item like Isaac or ??? can[[/note]], and The Lamb was never the TrueFinalBoss of the game since it made its debut in ''Rebirth'', so it was [[OvershadowedByAwesome upstaged by Mega Satan]] from the very beginning.]]
*** [[spoiler:Mega Satan has a total of 5,000 HP. Like Satan, this is split into two life bars for two separate phases (3,000 HP in phase 1 and 2,000 HP in phase 2). Also like Satan, Mega Satan's own HP by itself isn't the whole story; at certain HP intervals in the first phase, Mega Satan will retreat and summon some lower-grade bosses that you will need to kill before he returns to fighting and being susceptible to damage. While you ''can'' bypass the BossRush aspect of phase 1 by [[OneHitKill one-shotting it]] with a Chaos Card or Plan C, this will just advance to phase 2 rather than outright defeating Mega Satan. Oh, and just to add an extra dash of despair, Mega Satan's health bar isn't visible at all unless you have Spider Mod, though you ''can'' use the scripted sub-boss spawns in phase 1 and the [[ShowsDamage visibly-degrading sprite]] in phase 2 to have a rough idea of how well you're doing. While Mega Satan didn't have DamageReduction in ''Afterbirth'' or ''Afterbirth+'', he gained it in ''Repentance'' (and it's present for both phases), bringing his longevity up to around Hush's level with the scripted interruptions factored in.]]
*** [[spoiler:Ultra Greed has 3,500 HP and DamageReduction. While his raw longevity pales in comparison to Mega Satan or Hush, he does have a DefendCommand to drastically reduce the amount of damage he takes (which he tends to use after summoning minions), as well as the ability [[HealThyself to regain small amounts of HP]] with one of his random slot-machine coin minions (though the player can prevent this by killing said minions) or by picking up coins that his attacks knock out of the player (which the player can prevent by picking up the dropped coins before Ultra Greed can or just not getting hit in the first place). In Greedier Mode, he gains a second phase with 2,500 HP; this is a separate life bar (so you'll still have to deal with it the hard way if you use a Chaos Card in Phase 1, and you'll just kill yourself by using Plan C on phase 1) and loses the DefendCommand and minion-spawning in exchange for harder-to-dodge attack patterns.]]
*** [[spoiler:Hush's fight starts with a warm-up round against a reskinned ??? with only 1,000 HP. Once that's swept aside, Hush emerges in its true form, which has a colossal 6,666 HP and DamageReduction, not to mention enough BulletHell to have you constantly scurrying all over the BossRoom. It also periodically spawns flunkies to get in your way. At least Hush doesn't move around very much (much like Mega Satan), though it does have a couple of attack patterns where it retreats into the floor and becomes temporarily invulnerable. Oh, and as of ''Repentance'', it gains GradualRegeneration, though this only kicks in if you don't attack it at all for an unreasonably long time, and even then, only when it's almost dead. Chaos Card and Plan C are effective at skipping the full Hush fight, but using them on the ??? warm-up round will just be wasting them, and since Hush isn't actually the end-point of the run (at least after being defeated the first time), using Plan C on it without any extra lives ''will'' end up counting as a loss on your win/loss streak.]]
*** [[spoiler:Delirium has a whopping 10,000 HP, but while it does technically have DamageReduction, it doesn’t amount to much, since the scaling reduction resets every time Delirium [[VoluntaryShapeshifting changes forms]] (which it does ''very'' often). It makes up for this with its potential to change into bosses that can outright dodge or deflect your attacks, such as Scolex, Polycephalus, or Mom, as well as its own form-independent ability [[VillainTeleportation to outright teleport wherever it feels like being]] in its BossRoom at a moment's notice with absolutely no tells whatsoever. And just like its shapeshifting, Delirium uses its teleportation ''[[TeleportSpam frequently]]'', especially when it's heavily damaged. As such, [[GetBackHereBoss you'll be spending at least as much time trying to figure out where Delirium went and chasing it down to get back into position to attack it]] as you will be dodging its continuous BulletHell and whaling on it with your own tears/knives/missiles/whatever you're equipped with. (At least, when it doesn't decide to teleport ''[[TeleFrag right on top of you]]'' (good luck dodging that one, especially if you're playing as The Lost, The Keeper, or their Tainted versions and really need to avoid all damage at all costs.) Oh, and just for one more kick in the teeth, Delirium is ''[[NoSell completely immune]]'' to the Chaos Card, and its death animation is long enough that trying to cheese the fight with Plan C will result in the player dying before Delirium is officially defeated (meaning that you'll need to be Lazarus, have Lazarus' Rags, a Soul Stone of Lazarus, or Inner Child to actually be credited for the kill — and the former two only work for Lazarus' completion record). In other words, there is absolutely no way to cheese this fight.]]
*** [[spoiler:Mother has 4,222 HP, spread across two separate life bars (2,222 HP for phase 1 and 2,000 HP for phase 2), and yes, she has DamageReduction like the rest of the superbosses (and Chaos Card and Plan C only deplete one life bar). The first phase is immobile, but [[FlunkyBoss frequently spawns smaller enemies]] to get in your way (with one such attack pattern having Mother retreat into the wall and become invulnerable until she re-emerges for good measure, forcing you to focus on the minions to avoid being overwhelmed), while the second phase stops spawning minions but instead slowly chases Isaac around while firing BulletHell attacks, with one attack pattern in particular having another suddenly leap out of view before wildly dashing all over the room (obviously making it hard to aim at her until she settles down). Oh, and like Delirium, Mother's death animation takes longer than 3 seconds, meaning that Plan C will kill the player before Mother's death animation completes, denying the player the completion mark (or the opportunity to dash for the chest and finish the run) if they don't have an extra life. Unlike Delirium, even extra life items that kick the player out of the room won't undo a Plan C kill, so as long as the player wasn't dumb enough to use Plan C on phase 1, they can still get credit without having to redo the fight. Also, just like Mega Satan, Mother's health meter isn't visible without Spider Mod, and unlike Mega Satan, Mother has absolutely no other indicators of how close she is to defeat. Furthermore, she can't be one-shotted with The Bible.]]
*** [[spoiler:Dogma has 2,400 HP split across two life bars. In the first phase, Dogma's main body is invulnerable and the TV it's connected to is the actual target to destroy, which means that while the target is stationary, it has a meatshield to block your attacks with if you don't position yourself well. The second phase is more straightforward, with Dogma itself being the target, but it's mobile and has one attack pattern where it briefly leaves the BossRoom. And yes, both phases have DamageReduction.]]
*** [[spoiler:Each of the Ultra Harbingers has 2,000 HP (except for Ultra Pestilence, which has 1,800), and each of them has DamageReduction. None of them have any defensive measures in and of themselves (though the switch in perspective from a top-down DungeonCrawler to something akin to a side-scrolling ShootEmUp does make certain items, including bombs, considerably less effective, as gravity is suddenly a factor and they are liable to drop to the bottom of the screen). All in all, Dogma and the Ultra Harbingers are just a BossBonanza designed to wear the player down before they face the ''real'' TrueFinalBoss.]]
*** [[spoiler:The Beast has 10,000 HP, spread across three phases in a single life bar (but, like Delirium, she [[NoSell takes absolutely no damage from the Chaos Card]]; Plan C, on the other hand, is very effective). Aside from the same side-scrolling perspective as the Ultra Harbingers that screws with certain items, the Beast doesn't really have any defensive gimmicks aside from occasionally moving from one side of the screen to the other, either by charging or by ducking into the lava and popping up elsewhere. The Beast doesn't have a visible health meter, but she ShowsDamage, especially at very low HP.]]

** To provide hard HP numbers for all of the bosses we mentioned (and a couple that we didn't):[[note]]Bear in mind that your baseline damage output in this game is 3.5 per tear, so even the smallest of these numbers are going to take a while for weaker builds to reduce to 0.[[/note]]
*** [[spoiler:The "light path" Chapter 5 and 6 bosses, Isaac and ???/Blue Baby, have 2,000 HP each, and while they each have three phases, all three phases share the same life bar. The latter was the definitive TrueFinalBoss of the Flash version of ''The Binding of Isaac'' with the ''Wrath of the Lamb'' expansion.]]
*** [[spoiler:The "dark path" Chapter 5 and 6 bosses, Satan and The Lamb, are less straightforward. Satan himself (who was the TrueFinalBoss of Flash ''Isaac''[='=]s Halloween update]]) has only 1,200 HP, split across two phases[[note]]yes, in this case, that means that each phase has its own life bar]]; this is more than Mom's Heart/It Lives! (which has 1,000 HP), but still would be not quite enough to qualify as a MarathonBoss in this game if not for the fact that you need to go a round with The Fallen [[SequentialBoss immediately before Satan fights you]]. The Lamb has 2,600 HP (which used to be 2,000 before being buffed in a patch), divided in a single life bar across two phases. "Division" is taken literally in the second phase, as The Lamb splits itself into two entities, its head and its body, both of which have half of the remaining life meter and must be defeated to win the battle. We didn't mention either of these earlier because Satan's HP still isn't as impressive as Isaac or Blue Baby's even with The Fallen as a cushion, and The Lamb was never the TrueFinalBoss of the game since it made its debut in ''Rebirth'', so it was [[OvershadowedByAwesome upstaged by Mega Satan]] from the very beginning.]]

** ''Afterbirth'' adds Marked, which automatically fire tears at a target on the floor controlled by the player (like Epic Fetus but with tears).

* DiscOneFinalDungeon: [[spoiler:Chapter 3, where you fight Mom, is only the final part of the first completed run of the game. The following area, [[WombLevel Chapter 4]], was the original VeryDefinitelyFinalDungeon, where you fight Mom's Heart/It Lives. A Halloween patch added Sheol, accessible from a Devil Room on the Womb 2 or freely after It Lives has been unlocked, where you fight Satan. ''Wrath of the Lamb'' adds the Cathedral as an alternate final floor, with Isaac as its boss. The final patch of ''Wrath of the Lamb'' added the Chest, a follow-up to the Cathedral that ends with ???. ''Rebirth'' would add a dark counterpart to the Chest, the Dark Room, plus a TrueFinalBoss accessible from either floor.]] With ''Afterbirth+'', [[spoiler:a new dungeon was added: the Void. Due to the nature of accessing it, the Void can be reached after nearly any earlier floor to serve as a final level]].

** Many items (such as Loki's Horns, Rubber Cement, and Cricket's Body) do not synergise well with Ipecac, usually because they make your explosive shots travel in an unusual path which leads to them blowing up right next to you. The Suicide King Challenge enforces this by starting you with Ipecac + My Reflection, so your shots boomerang around and come back to hit you in the face.
** Dr. Fetus doesn't have as many bad synergies as Ipecac, but the ones which it does are arguably even worse because the bombs explode after a time delay rather than on contact with an object. This means that even if you aim your bombs perfectly, they'll still come back to hit you.

* FlunkyBoss: A few bosses get their difficulty from swarming the player with enemies that act as meatshields at the very least. The Duke of Flies, the dark-shaded version of Gurdy, and Mom herself are the best examples of flunky bosses that summon enemies during battle. However, Monstro is the best example of a flunky boss that can't summon enemies. In the Flash version of ''The Binding of Isaac'', Monstro can spawn with two Black Flies in his boss room. Rebirth expanded the amount of monsters Monstro can spawn with, including two Attack Flies, two Gapers, two Hoppers, two Mulligans, or four Frowning Gapers. Later expansions let Monstro spawn with two Cyclopias or four Ministros.

** While they usually just feature Isaac getting humiliated in some way, one of Isaac's between-level nightmares shows him suffocating inside of a chest, [[spoiler:foreshadowing the Sheol ending and ???'s possible origins]]. Another nightmare shows Mom getting the message from God, only to cut to [[spoiler:Isacc's ghost/The Lost in the attic, hinting at the fact that most of the game and lore are Isaac's own creation]].

** ''Wrath of the Lamb'''s had a bug at launch that caused [[spoiler:the Polaroid to replace Isaac with the wrong TrueFinalBoss when brought to the Cathedral]]. The boss screen shows [[spoiler:???'s image with the name "Daddy Long Legs"]], and the fight itself was with [[spoiler:VideoGame/{{Triachnid}}, an alternate version of Daddy Long Legs in the same vein as past references to Edmund [=McMillen=]'s games like Steven, C.H.A.D., and Gish; Triachnid was intended to be DummiedOut but accidentally replaced a plot-important boss]]. Conveniently, ''Wrath of the Lamb'' was the first expansion to start elaborating on [[spoiler:Isaac's dad (Triachnid is a father in his origin game)]], so it wasn't widely realized as a mistake until patches restored [[spoiler:??? and Triachnid]] to their intended places.

*** As of ''Repentance'', there's an even Infinity +1-er counterpart to the aforementioned item. In Afterbirth+, the [[spoiler:D Infinity]] acted as a random dice item upon being activated. However, in ''Repentance'', it was buffed so that rather than being random, you can ''choose'' which die effect the [[spoiler:D Infinity]] activates, meaning that it allows you to choose from the effects of each of the D1, the D4, the [[spoiler:D6 and its Eternal counterpart]], the D7, the D8, D10, the D12, and the D20. [[spoiler:Unfortunately, the D Infinity doesn't have a Spindown Dice form.]] Unlike the D100, though, you can ''choose'' to only isolate a particular effect, [[spoiler:which is most useful with the D6 effect]].

** ''Repentance's'' [[spoiler:Tainted characters]] all serve as sidegrades to [[spoiler:their originals]], holding significant upsides at the cost of significant downsides, but one that could truly be called this is [[spoiler:Tainted Lost]]. On the plus side, he will never find items that [[spoiler:would otherwise be useless to The Lost]]. On the downside? [[spoiler:He only starts with a Holy Card instead of an intrinsic Holy Mantle, and he lacks the Eternal D6.]] Even worse, his upside is also a double-edged sword [[spoiler:as it also prevents him from finding many items that ''would'' be useful to the Lost. To give a few examples, you can't find any form of extra life items (unless you know how to [[GuideDangIt force them to spawn]])]]. Oh, [[spoiler:and the ''Holy Mantle'' isn't available to Tainted Lost, either, just in case you thought that not starting intrinsically with it wasn't enough of a downside]].

* LethalJokeCharacter: The soul heart mechanic of [[spoiler:???]] lends itself to some amusing exploits that give him an edge. He registers as having no health due to lacking red hearts, so he always has the maximum devil/angel room chance, can always enter challenge rooms, and gains permanent use of low-health effects like the Polaroid and Whore of Babylon. He also benefits greatly from items that affect red heart drops or consume them, such as the Mitre and Dark Bum.

** The Bible grants flight for a room and doesn't recharge for another six (barring other items to increase charge time), but kills the final boss and the original two {{True Final Boss}}es in one use. However, using it on Satan [[PressXToDie just kills you]], and against every later boss, it'll just deal no damage.

** Perfection is a trinket that grants 10 Luck when held, which significantly boosts the power of any item that synergizes with luck. However, you need to play three floors without taking damage and upon taking damage, you lose Perfection even if you smelted it, making it a difficult item to get and maintain. However, in the hands of the Lost, who has to play perfectly anyway, it can easily propel him to GlassCannon.

** Every single playthrough, due to the randomized nature of the game. You can never guess if items will complement each other, or if they'll even be useful, including boss drops and shop inventory. Key and bomb drops can either leave you with a surplus or lock you out of chests and treasure rooms if you fall short. The good stuff in the shop costs just enough that you probably won't be able to pay for it until you've gone down three or four levels, when Greed loves to lay its ambushes. Pills are always random and are just as often bad as good (unless you have the Lucky Foot or [=PhD=]). Slot machines and the like won't pay out half the time without good luck. There is always a chance that you will reach the end of the game with a much more or less powered up character than you expected through no fault of your own. On the extreme, it's possible to get absolutely no useful upgrades, all bonuses being activated items that you do not want, or things your character doesn't benefit from at all. On the other hand, it's possible to get an item combination that absolutely dominates everything. That said, due to the way items are unlocked, each successful playthrough means it is more likely items will be useful, and the fact that the game gets longer means more items to find. The first playthrough is often the toughest.

** The Wafer makes anything that hurts you do exactly one half-heart of damage. It does almost nothing for the first half of the game (where only Champion enemies, spikes, collision with bosses, and your own bombs hurts for more than that), but starting at the Womb, everything does a full heart of damage, so the Wafer effectively doubles your health and any health pickups.

** The Bible allows you to fly for a single room. While useful, there are items that grant this effect permanently and don't take up your special item slot. It also has the slowest recharge rate possible, so you only get flight once every six rooms (without upgrades). But, if you use it on Mom and Mom's Heart/It Lives, they die instantly, allowing you to bypass two of the hardest bosses in the game and making the NoDamageRun in each section a lot easier. Unfortunately, it doesn't work on other major bosses, making it useless to keep holding onto past that point — and items are ''much'' harder to find after the Womb.

** If your damage output doesn't scale as you progress through the game, later bosses can take an obscene amount of effort to kill. This is especially true of [[spoiler:Isaac]] and [[spoiler:???]]. And then there's [[spoiler:Mega Satan]] of ''Rebirth'', who takes forever without the Chaos Card due to being a BossRush as well as a regular boss.
** ''Afterbirth'' adds in [[spoiler:Hush]] and [[spoiler:Ultra Greed]], who are unique in that their HP is scaled so you won't wind up with a combo that can kill them in twenty seconds. No matter how well-prepared you are, expect to spend a lot of time killing them.

Gameplay follows Isaac as he descends into the labyrinth underneath his house. Isaac wanders the maze that is the basement and beyond, collecting items and trinkets to slowly amass enough power to survive a confrontation with Mom and eventually greater foes beyond. The player visits item rooms to acquire powerful upgrades and faces off against a boss on every floor, heading deeper and deeper downwards with each room cleared. The game utilizes procedural generation to make each playthrough a unique experience, while additional characters themed after important people from Abrahamic myth can radically change how the game plays. Variety is the name of the game here, and the sheer volume of rooms, bosses, items, characters, secrets, challenges and endings ensures that no two runs through the basement will ever be the same.

* ''Repentance'', another expansion for the remake, released on March 31st of 2021. The expansion is an UpdatedRerelease of the ''[[VideoGame/TheBindingOfIsaacAntibirth Antibirth]]'' GameMod, featuring the alternate path and expanding on it with new secondary floors, a plethora of new items (a good number of which [[CanonImmigrant originating from]] ''[[CanonImmigrant Four Souls]]''), and a new set of alternate forms for each playable character. It also improves the co-op mode by allowing players to use full-fledged characters rather than babies, and includes a metric boatload of quality-of-life changes to previous content. The release date trailer for this expansion can be found [[https://www.youtube.com/watch?v=gOaWadhNi0A here]].

** ''Repentance'' introduces Inner Child, which also shrinks the character upon revive. Notably, being revived by Inner Child revives you on the spot instead of to a previous room, enabling you to take out whatever killed you [[spoiler: and making a non-Lazarus Plan C Delirium kill viable.]] It is also notably one of the very few items with a fixed spawn: [[spoiler: it's in the crawl space in Home for Tainted characters and characters that already unlocked their Tainted variant.]]

* DynamicDifficulty: Individual runs don't change depending on how well/poorly you do, but the game itself slowly changes the more times it's beaten, starting with unlocking more levels/bosses after Mom. After a while, more advanced versions of bosses replace their predecessors and other bosses change too, such as the Harbingers appearing after Mom is beaten for the first time. Most notoriously, beating the game many times would steadily increase the chance that The Fallen would randomly replace a regular boss and would frequently [[ClassicVideoGameScrewYous appear on the first or second floors]]. On the other hand, unlocking more and more items with each completed run and experience with the game mechanics counteract this, keeping things more-or-less fair.

** "Mama Mega!", when used, kills every normal enemy in a room (if an enemy spawns another upon death, you have to kill them yourself), does massive damage to bosses, destroys all forms of rocks (but not Keepers or rocky chests), opens all Secret and Super Secret Rooms, and even opens the paths to Boss Rush and the Blue Womb if you've passed the time limit for either. Best of all, it lasts for the entire floor on which it is used, giving you an entire "free" floor with nothing standing in your way. The only downside is that it can only be used once before going away unless you picked up a Gold Bomb.

** One of ''Rebirth'''s Dice Rooms has the same effect as Forget Me Now.

* PowerupMagnet: There's a [[ComicBook/{{Magneto}} "Magneto"]] powerup which attracts powerups even through rocks and over gaps.

* DunceCap: The Wiz powerup in ''Afterbirth'' is a dunce cap that gives the player character permanently crossed eyes (similarly to the "r u a wizard" pill) that makes them constantly fire at diagonals.

* EasterEgg: Using an Inverted Chariot card, which turns Isaac to a stone statue, has a low chance of that stone statue resembling Edith, a character planned for ''Repentance'' but ultimately cut.

''The Binding of Isaac'' is a HorrorComedy, BlackComedy, {{Roguelike}} Top-Down Shooter made by Creator/{{Edmund McMillen}} and Florian Himsl, released in September 2011.

The story follows [[MeaningfulName Isaac, a young boy]] who finds himself in possibly the worst situation imaginable. After his [[TheFundamentalist fanatical Christian]] mother begins [[HearingVoices hearing the voice]] of {{God}}, she removes all of his worldly possessions and [[NakedOnArrival strips him naked]], confines him to his bedroom, and unhesitatingly accepts a commission to kill him in sacrifice to prove her devotion. Isaac discovers her intentions and manages to escape into [[DungeonCrawling the basement]], where, still naked, he goes on the run as he fights off nightmares both physical and mental (using [[AbnormalAmmo his own tears]], no less), discovers memories of his own past, and ultimately confronts [[BigBad Mom]] in an effort to survive.

* NoFairCheating: Level seeds allow you to repeat a powerful run, but block any achievements. Special seed effects that make the game easier (such as making Isaac invincible or causing all enemies to become permanently charmed) will also block achievements. Similarly, every challenge run only allows you to unlock the associated achievement. Finally, the "Victory Lap" mode blocks any achievements, other than ones associated with it specifically.

* AsteroidsMonster: The bosses Envy, Blastocyst, Fistula, and Teratoma split into multiple smaller forms as they lose health. A few normal enemies such as Moters (two connected flies) have the same trait.

* VariableMix: If a room has a lot of enemies or there's a miniboss, an electric guitar harmony fades into the music.

A [[VideoGameRemake remake]], ''The Binding of Isaac: Rebirth'' developed and published by US-based independent game studio Creator/{{Nicalis}}, which overhauls almost every aspect of the game, has since been released on PC, Vita and [=PS4=] on November 4, 2014. It has a rather creepy [[https://www.youtube.com/watch?v=OLtZW3xIix0 trailer]] (and an even [[UpToEleven creepier]] one [[https://www.youtube.com/watch?v=1aBb0M8HRCQ here]]). ''Rebirth'' boasts a new engine, a larger development team, even more items, better synergies between said items, and more new content. Ports for the Wii U, New 3DS, Xbox One, and Nintendo Switch have also been released.

** Any Rainbow item (including the 3 Dollar Bill) will have randomized tear effects that change every three seconds, such as the Rainbow Baby having a random effect for every individual tear. The Pride Day Challenge in ''Afterbirth'' has you [[UpToEleven equip all of them at once]], allowing them to stack with different random combinations.

** Dr. Fetus allows you to shoot bombs instead of tears. On one hand, it can hurt you and it takes good timing. On the other hand, you have limitless bombs (enabling you to clear out rocks and get to items and secrets more easily), and enemies and bosses die really easily. This is taken UpToEleven with the Ipecac Syrup in ''Wrath of the Lamb'': it does more damage than bombs and poisons on hit, but its arcing path is very difficult to work with. ''Rebirth'' introduces items like Host Hat and Pyromaniac that block explosive damage or cause it to heal Isaac, making bomb attacks basically always worth using.

* FlunkyBoss: A number of new bosses spawn monsters while fighting them, such as [[ToiletHumor Brownie summoning Corn Dips]] (or Chargers, if you're fighting the Champion version). [[spoiler:Mega Satan]] [[UpToEleven kicks it up a notch]] and can summon bosses in the form of any of the regular Sins [[MyFriendsAndZoidberg and occasionally The Hollow]].

* MadeOGold: The player can find a lot of collectables made of gold, such as hearts, bombs, batteries, and [[UpToEleven even pills!]]

** [[spoiler:''Repentance'' takes this UpToEleven by having a Secret Alternate character for every character in the roster, including the Secret Characters listed above. To get a character's alternate, you need to use the Red Key or Cracked Key in a certain room in Home as that character.]]

* UpToEleven: ''Afterbirth'' has the XXXXXXXXL challenge, which is the "XL" level effect on steroids. All levels have a size which is roughly equal to an XL Womb level.

[[JustForFun/TVTropesWillRuinYourLife Today I died]]. I was killed by this page on [[Wiki/TVTropes some wiki]]. [-(ugly)-]\\

Gameplay follows Isaac as he descends into the labyrinth underneath his house. Isaac wanders the maze that is the basement and beyond, collecting items and trinkets to slowly amass enough power to survive a confrontation with Mom and eventually greater foes beyond. The player visits item rooms to acquire powerful upgrades and faces off against a boss on every floor, heading deeper and deeper downwards with each room cleared. The game relies on a lot of Random Generation to make each playthrough a unique, while additional characters themed after important people from Abrahamic myth can radically change how the game plays. Variety is the name of the game here, and the sheer volume of rooms, bosses, items, characters, secrets, challenges and endings ensures that no two runs through the basement will ever be the same.

** Most [[EliteMooks Champions]] are color-coded (with the exception of the size and "pulsating" variants), based upon the additional abilities they have and what items they drop when they are killed:

*** Green Champions have increased health, leave a damaging trail of creep and drop pills.
*** Pink Champions have increased health and randomly launch projectiles, but don't spawn anything upon death.

*** Transparent and white Champions can move through obstacles that would obstruct it normally, like pits and rocks. They drop golden chests upon death.

*** Black (well, more of a dark green) Champions have increased health, explode when killed and drop bombs.
*** Dark red Champions will turn into a pile of red mush when killed which, if not killed within a short amount of time, [[RevivingEnemy will regenerate and begin attacking Isaac]], similar to a Globin.

* BlackComedy: The entire game is front-to-back and head-to-toe with dark comedy. Power-ups include the severed body parts of beloved pets (which act as damage-ups, given that the game [[AbnormalAmmo weaponises tears]]), a wire coat hanger ([[TruthInTelevision a common home-made abortion tool in real life]] which amps up Isaac's tears), several items that increases Isaac's health and attack power implies his less-than-stellar home life (Breakfast, Dinner, Lunch, Tough Love) and various ([[MindScrew possibly]]) aborted or otherwise dead siblings of Isaac's including Brother Bobby, Sister Maggy, and [[NightmareFuel Harlequin Baby]] (who act as [[{{Familiar}} combat companions]]). Hell, there's even a SecretCharacter [[spoiler:in the form of a cyanotic corpse]].

** Shooting the poop and fires in every room. Most of the time you get nothing, but sometimes you get hearts, money, or even the Petrified Poop trinket (which increases the chance you'll find something in the poop, even super-rare pickups like eternal hearts). When you're low on health, but have plenty of time, shooting the poop can be a life-saver.

*** Yellow Champions are faster than their non-colored counterparts, and drop a battery.

** You're guaranteed some of these in one of the last secret floots, [[spoiler:The Chest]], as long as you have keys -- four golden chests are guaranteed in the starting room and every chest in the level has an item in it.

** The v1.03 update to ''Rebirth'' has a nasty one (that some people initially thought was an intentional change just to make the game harder). You can not bomb into special rooms (Treasure Room, Shop, Sacrifice Room, etc.) from Secret Rooms. This can lead to {{Unwinnable}} situations where you can use The Moon or Telepills to enter the Secret Room and find out that it ''only'' borders special rooms, giving you no way out.

* KillEnemiesToOpen: Every room containing enemies will automatically shut itself down until you kill them all. It's possible to force your way out of a room containing enemies by hitting the door with an explosion, either yours or one from an enemy. This tactic must be used sparingly because bombs are a precious commodity most of time unless your have an item that replicates them, and doing so doesn't take care of the enemies inside the room, so if you walk back into it, you'll either have to deal with the enemies or use another bomb to escape once again. Also, this tactic doesn't work in boss/mini-boss battles, because their doors are blast-proof. [[spoiler:It also doesn't work on doors in the Chest or Dark Room.]]

** The Spindown Dice added in ''Repentance'' rerolls all items in a room to the previous item in the list (in other words, one item ID lower). Assuming you know what items will reroll into (or look it up), you can reroll some very powerful items from common things. For example, if you donate enough to a Blood Bank to spwan a Blood Bag item, it can be rerolled into a free and guaranteed Brimstone, since Brimstone's item ID is one below Blood Bag.

** Every single playthrough, due to the randomized nature of the game. You can never guess if items will complement each other, or if they'll even be useful, including boss drops and shop inventory. Key and bomb drops can either leave you with a surplus or lock you out of chests and treasure rooms if you fall short. The good stuff in the shop costs just enough that you probably won't be able to pay for it until you've gone down three or four levels, when Greed loves to lay its ambushes. Pills are always random, and are just as often bad as good (unless you have the Lucky Foot or [=PhD=]). Slot machines and the like won't pay out half the time without good luck. There is always a chance that you will reach the end of the game with a much more or less powered up character than you expected through no fault of your own. On the extreme, it's possible to get absolutely no useful upgrades, all bonuses being activated items that you do not want, or things your character doesn't benefit from at all. On the other hand, it's possible to get an item combination that absolutely dominates everything. That said, due to the way items are unlocked, each successful playthrough means it is more likely items will be useful, and the fact that the game gets longer means more items to find. The first playthrough is often the toughest.

** Bosses also contribute to the luck-based nature of the game. Not all of them are equally difficult, and depending on which character you choose and which powerups you get, some might be a cake-walk (Larry Jr., Loki) and some an endless source of frustration (Gurdy for a slow-moving character, Monstro II for people who dislike close-range combat, or The Bloat for pretty much everyone). Since not getting hit (which is more difficult if you get a boss you are faring poorly against) is almost a requirement for getting access to the devil room, which often allows one to balance the odds, [[UnstableEquilibrium the difficulty snowballs depending on how much]] the RandomNumberGod loves or hates you.

* NintendoHard: Much like the {{Roguelike}}s it's based on, ''The Binding of Isaac'' has no continues. You start with one life and additional lives are very, very unlikely to show up once along multiple playthroughs, much less a single one. If you die, you start all over again. The configurations of rooms and upgrades are randomized, and in some situations damage will be nearly unavoidable. Survival depends on reflexes and calculated risk. Each expansion to either the Flash original or ''Rebirth'' tends to turn the difficulty up a few notches.

** The Beelzebub transformation gives you flight, and makes all enemy flies into friendly blue flies. Unlike Guppy, it doesn't let you create flies by attacking, so its main effect dries up once fly enemies become uncommon on later floors. The upside is that it's much more likely to get three fly-related items than three Guppy items (and most Guppy items require hunting for red chests and devil deals), so it's a more common transformation to get.

* SerialEscalation: Every successive expansion (or installment in the case of ''Rebirth'') ups the amount of powerful items, synergies, bosses, floors, and rooms.

* SpikesOfDoom: Floor spikes appear in later levels in some of the rooms, and deal a full heart of damage no matter where they're found.

** The 3 Dollar Bill's name comes from an old saying that something is "as queer as a three dollar bill", back when "queer" meant "strange" and not "homosexual". The Bill also makes Isaac happy, or to use another term, ''gay'', back when the word meant "happy, of good cheer" and not its modern meaning. But keeping with the more modern definition of "gay", it gives Isaac a random tears effect every three seconds, which the game describes as "Rainbow Tears". The ''Afterbirth'' challenge themed around it is even called Pride Day.

** Your reusable item can only be replaced with a different one, though depending on the character, you might start out empty-handed. Likewise, you can only drop a one time use item by picking up a different one, which can be stressful if you end up holding one you know would be detrimental to your health if you accidentally used it.

** The alternate path in ''Repentance'' features a sidequest that unlocks its exclusive final floors and boss, [[spoiler:Mother]]. Defeating it once allows another secret to be reached on any path[[note]]or, rather, before the branching point that locks in the route[[/note]], whichs leads to a floor containing two more final bosses, [[spoiler:Dogma]] and [[spoiler:The Beast]]. These are considered the definite true final bosses of the game (so long as no more expansions get added), and beating them unlocks one last ending.

** In general, having better items means doing better overall and and allows the player to take more risks, which in turn may improve the player's position. Doing well on the first floors greatly increases your chances of getting through the entire game. On the other hand, it's not as easy to turn things around if the first floors treat you especially badly.

* AnimationBump: The game is a slightly pixellated {{Retraux}} style. The endings, however, are very fluidly animated.

** To access [[spoiler:Home]], you need to get either the Polaroid or the Negative to unlock the door to a special version of Mausoleum/Gehenna II. To get them, you must defeat Mom, and her room has no exit door; therefore, you need a way to teleport out of it. For that purpose, there's a guaranteed way to obtain a a Fool card (or a Telepills pill if you happen to have Little Baggy, which overwrites card spawns): [[spoiler:break the marked skull on Depths II/XL or its alternate versions. This doesn't work in Mausoleum or Gehenna because there is no special door at the beginning there]].
** To unlock [[spoiler:the Tainted version of a character]], you need to use either the Red Key or a Cracked Key in a certain spot the final chapter. The first time you reach that final chapter, you are guaranteed to find the former right before the SequentialBoss. Alternatively, you can spawn the latter by [[spoiler:leaving a trinket in a treasure room or a boss room. After you go through the special door and climb back back to that particular floor, re-enter that room and you'll find a Cracked Key on the ground]].

** In order to obtain [[spoiler:Godhead]], you need to collect collect all the completion marks on Hard mode for a bonafide JokeCharacter, one of the hardest tasks in the game. It's a fantastic item that ranks among the best in the game, with tons of positive synergies, but if you can perform that well you may not need it when it does show up.

** ''Afterbirth+'' has another fine example in the form of [[spoiler:Delirium, the new TrueFinalBoss. He combines complex bullet patterns with impredictable shapeshifting and erratic TeleportSpam. Add his massive amount of [=HP=] and you have a pretty challenging boss on your hands]].

** Spood Bender plus Technology 1 or 2. The laser beam actually curves itself around to hit enemies.

** [[{{Denouement}} While needing to be pieced together from multiple different endings]], the endings added by the expansions [[spoiler: (as well as the an ending in ''The Legend of Bum-bo'' and [[https://twitter.com/edmundmcmillen/status/1385112195772473348 Word of God]])]] make it clear. [[spoiler:[[TheHeroDies Isaac suffocates to death]] inside the chest trying to hide from his abusive mother. He is [[DyingDream hallucinating the entire game]] due to asphyxiation fuelled delirium and his father encouraging him to use his imagination as a coping mechanism. His mother believes him to be missing and after an indeterminate period of time she finds his remains and mourns his death. Isaac's fate in the afterlife, however, is ultimately unknown and is left up to interpretation]].

** ''Every'' boss (with the exception of end-of-chapter bosses and minibosses) can become this with ''Repenance's'' "Vanishing Twin" item, which spawns a familiar that then turns into a copy of the floor's boss when you enter the boss room. To compensate, the health of each boss is reduced to 75%, their attack and movement patterns are slowed down slightly, and you receive an additional item from the boss copy when you defeat it.

** [[spoiler:Delirium]] is meant to be completely immune to the [[OneHitKill Chaos Card]]. but when it gain multiple hitboxes, it becomes vulnerable, which isn't supposed to happen and causes a game crash.

** The TMTRAINER item added in ''Repentance'' turns all items found from that point on into "glitch items" that have completely random effects. But while ''most'' of the essential items are protected from being glitched, [[spoiler:Dad's Note]] is not, which can cause the game to softlock when you enter the room it's contained in. The November 2021 update fixed this by making it and other"quest" items immune to TMTRAINER's effect.

** Two stats are not shown on the stats screen, or elaborated upon at all. You have "Evil / Faith", which is a sliding scale determining what kind of special deal (Devil Room or Angel Room) you get when you qualify for one, and Shot Height, which is used as an alternative to range in some items that claim to increase it (notably, increasing Shot Height as Azazel is a bad thing and makes his range shorter). ''Afterbirth+'' added a Found HUD option that displays the former among other stats, but not the latter.

** The Dice Rooms in ''Afterbirth'' have their effects determined by the number of pips on the floor, and can reroll things from your current load out to all the pedestal items on the floor to the floor itself. The game doesn't tell you what these effects are or which ones correspond to which rooms. You'll have to find out by using them or looking it up. Downplayed in ''Afterbirth+'' where the Dice Rooms now have markings that hint at what they do (for example, an image of a D4, D6, or Forget Me Now for the aforementioned three). Of course, if you're new to the game you probably won't know what those markings actually mean.

** The Void item added in ''Afterbirth+'' has two properties. This first, which is moderately useful, allows it to destroy any passive items in a room and covert them into random stat boosts, with a chance for a slight range reduction. The second, which applies to this trope, allows it to destroy any spacebar items and permanently copy their effects. There is no limit to how many items can be absorbed this way, and all of them will trigger each time Void is used. This can include generating Soul Hearts, Black Hearts, Eternal Hearts, mapping a floor, using Blank Card and its combos, Placebo and its combos (most importantly, infinite charge), four-way Brimstone from Krampus, and so forth. The only things it can't copy are spacebar items that are consumed upon use.

* NintendoHard: A "hard" difficulty level has been added, which significantly dials up the amount of enemies and [[EliteMook champions]] while giving you less powerful items, and in ''Repentance'' it allows low-tier shops to spawn regardless of the Donation Machine's coin count. ''Afterbirth+'' does this for Greed Mode, which is called Greedier Mode.

** Normally, range upgrades are very underwhelming compared to damage or tears upgrades due to to most characters already having adequate range. Azazel inverts this by having high damage output right out of the gate but very low range. Downplayed in that range upgrades only affect his mini-Brimstone to a small degree, but stacking more than one of them is still hugely helpful for the lategame bosses.

** The R Key allows you to start the run over from the very beginning, keeping items in tact. This allows you to basically do a [[NewGamePlus Victory Lap]] without any of the downsides.

* NiceHat: The Host Hat, an item introduced in ''Afterbirth''. It's a [[ExactlyWhatItSaysOnTheTin Host that Isaac wears on his head]]. It protects Isaac from explosions, falling rocks from above, and has a chance to block incoming shots and counter with the Hosts' signature three-bullet spread. The item's in-game description is even "Nice hat!"