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* WaveMotionGun: After you finish her first face, her head retreats back into the wall before firing a ''huge'' laser at you. Can also be a nasty surprise for ''Antibirth'' vets, as The Witness ''didn't'' do this.
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* WaveMotionGun: After you finish her first face, phase, her head retreats back into the wall before firing a ''huge'' laser at you. Can also be a nasty surprise for ''Antibirth'' vets, as The Witness ''didn't'' do this.
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* WaveMotionGun: After you finish her first face, her head retreats back into the wall before firing a ''huge'' laser at you. Can also be a nasty surprise for ''Antibirth'' vets, as The Witness ''didn't'' do this.
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* KnightOfCerebus: Every enemy encountered in the game so far had been a gross, disgusting monster or a child's interpretation of something from the Bible. Every demon or angel thus so far looked like how a child would likely see them, or just have some slightly funny quirk about them. Dogma is ''neither''. Instead of being another faceless angel like Uriel and Gabriel, it resembles how something like an Ophanim would actually look in the Bible, has music that is barely even music and more insane preachers screaming of sin, and the implications of the impact it has on the story means what it represents has done more to cause the story than almost any other boss in the game.
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** Further averted in ''Repentance'', where you have to beat Hush 3 times to unlock the alternate floors from ''Antibirth''.
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* MeaningfulName: A "dogma" can be described as "a belief or rule that is held onto deeply and fervently despite the lack of basis in its authority". As a representation of televangelism, it represents the fact that many televangelists speak with a false authority on the meaning of God's words.
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[[folder:"Mother"]]
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[[quoteright:194:https://static.tvtropes.org/pmwiki/pub/images/boss_the_beast.png]]
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[[quoteright:194:https://static.tvtropes.org/pmwiki/pub/images/boss_the_beast.png]]
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[[quoteright:110:https://static.tvtropes.org/pmwiki/pub/images/boss_dogma.png]]
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[[quoteright:194:https://static.tvtropes.org/pmwiki/pub/images/boss_the_beast.png]]
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* FeatherFletchette: One of its second form's attacks involves assuming a ring-like form and spinning like a top and passing through a wall. Upon impact, a storm of feathers sprays outward towards your character.
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* FeatherFletchette: FeatherFlechettes: One of its second form's attacks involves assuming a ring-like form and spinning like a top and passing through a wall. Upon impact, a storm of feathers sprays outward towards your character.
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* AnthropomorphicPersonification: It is one of televangelist sermons, and more specifically, the corrupt and fanatical version of religion used by deranged fundamentalists... like what Mom subscribed to. Tellingly, its first form is literally linked to the television it pops out of, and its second form looks like a StarfishAlien of an angel.
* AmbiguousGender: It has no defining features of any kind outside of being composed of TV static, so any gender it has, if at all, is unknown.
* AmbiguousGender: It has no defining features of any kind outside of being composed of TV static, so any gender it has, if at all, is unknown.
* DeliberatelyMonochrome: Applies to both itself (being made of TV static and all) and its boss arena, where the entire screen, barring you, your familiars (if any) and your attacks, is rendered in greyscale.
* FeatherFletchette: One of its second form's attacks involves assuming a ring-like form and spinning like a top and passing through a wall. Upon impact, a storm of feathers sprays outward towards your character.
* FeatherFletchette: One of its second form's attacks involves assuming a ring-like form and spinning like a top and passing through a wall. Upon impact, a storm of feathers sprays outward towards your character.
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* GreaterScopeVillain: Dogma is the personification of the demented fundamentalism which led to Mom's descent into religious madness. It's essentially the source behind all of the negative influence that Christianity had on Isaac, and is thus a significant contributor to Mom's antagonism.
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* FreezeFrameBonus: In its second form, sometimes its sprite gets replaced by what looks like a large, crying Isaac face for a split second.
* GreaterScopeVillain: Dogma is the personification of the demented fundamentalism which led to Mom's descent into religious madness. It's essentially the source behind all of the negative influence that Christianity had on Isaac, and is thus a significant contributor to Mom's antagonism. And yet, it does not appear at all in the game until you reach the Home area.
* HellIsThatNoise: A lot of its sound effects include distorted static noises and buzzes that grate on your ears.
* GreaterScopeVillain: Dogma is the personification of the demented fundamentalism which led to Mom's descent into religious madness. It's essentially the source behind all of the negative influence that Christianity had on Isaac, and is thus a significant contributor to Mom's antagonism. And yet, it does not appear at all in the game until you reach the Home area.
* HellIsThatNoise: A lot of its sound effects include distorted static noises and buzzes that grate on your ears.
* MindScrew: Probably one of the most mind-screwy of bosses, as it's a being that looks like a fetus connected to a television and made of static, then shifting into an eldritch angel form in its second phase while a preacher rants and raves in the background.
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* SmallRoleBigImpact: Is only the subject of one relatively short boss fight, but its influence on Isaac's life is far-reaching.
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* PaintingTheMedium: Its health bar is not the standard blood red that other bosses have. Instead it's composed of the same static that it has as part of its sprite.
* SmallRoleBigImpact: Is only the subject of one relatively short boss fight, but its influence on Isaac's life is far-reaching. In another sense it applies to the fight with the Beast, as the static cross it forms after being killed falls on Isaac and grants him angel wings in order to be on equal footing with the Beast.
* SmallRoleBigImpact: Is only the subject of one relatively short boss fight, but its influence on Isaac's life is far-reaching. In another sense it applies to the fight with the Beast, as the static cross it forms after being killed falls on Isaac and grants him angel wings in order to be on equal footing with the Beast.
* TheLastOfTheseIsNotLikeTheOthers: The majority of the game's bosses and enemies are composed of either BodyHorror, ToiletHumor, NauseaFuel, or some combination. Alternatively they are meant to represent various characters from the Bible, outright demonic creatures, or just thematically appropriate entities based on the area they're in. Dogma... is none of these. Instead it's a being composed of TV static that looks like a fetus connected to the TV it comes out of, and shifts into an AngelicAbomination form after said TV is destroyed. It is truly one of the weirdest monsters in the game, if not THE weirdest.
* OurMonstersAreWeird: Certainly one of the more out-there bosses in this game.
* OurMonstersAreWeird: Certainly one of the more out-there bosses in this game.
* ShowsDamage: As it takes more and more punishment, it starts bleeding, losing teeth, eyes, and its horns.
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* TrueFinalBoss: Of Repentance.
* UnexpectedShmupLevel: Isaac sprouts wings and takes flight to do battle with the Beast and his Horsemen.
* UnexpectedShmupLevel: Isaac sprouts wings and takes flight to do battle with the Beast and his Horsemen.
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* ThirdEye: It has an extra eye, though doesn't seem to do anything with it.
* TrueFinalBoss: OfRepentance.
Repentance, and as of this writing, the entire game itself.
* UnexpectedShmupLevel: Isaac sprouts wings and takes flight to do battle with the Beast andhis Horsemen.its Horsemen.
* VacuumMouth: It does this to draw in fire and try to swallow you, before finishing with a huge laser.
* WaveMotionGun: It uses a humongous version of Brimstone as one of its attacks.
* TrueFinalBoss: Of
* UnexpectedShmupLevel: Isaac sprouts wings and takes flight to do battle with the Beast and
* VacuumMouth: It does this to draw in fire and try to swallow you, before finishing with a huge laser.
* WaveMotionGun: It uses a humongous version of Brimstone as one of its attacks.
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* TookALevelInBadass: Unlike the other bosses from ''Antibirth'', which came over to Revelations relatively unchanged, Mother's actually harder than she was when she was the Witness. To start with, the room is no longer a large 2x2 room, meaning you don't have as much room to maneuver. On top of this, she has a lot of new attacks, and some of her old ones have different properties.
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* TookALevelInBadass: Unlike the other bosses from ''Antibirth'', which came over to Revelations Repentance relatively unchanged, Mother's actually harder than she was when she was the Witness. To start with, the room is no longer a large 2x2 room, meaning you don't have as much room to maneuver. On top of this, she has a lot of new attacks, and some of her old ones have different properties.
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* TookALevelInBadass: Unlike the other bosses from ''Antibirth'', which came over to Revelations relatively unchanged, Mother's actually harder than she was when she was the Witness. To start with, the room is no longer a large 2x2 room, meaning you don't have as much room to maneuver. On top of this, she has a lot of new attacks, and some of her old ones have different properties.
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The Beast of the Apocalypse, heralded by the Four Horsemen. Repentance's TrueFinalBoss (for real this time), The Beast challenges Isaac after his victory over Dogma.
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The Beast of the Apocalypse, the Mother of Harlots, heralded by the Four Horsemen. Repentance's TrueFinalBoss (for real this time), The Beast challenges Isaac after his victory over Dogma.
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* AmbiguousGender: The beast's gender isn't specified, even during the cutscene taking place after the battle.
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* AmbiguousGender: The beast's gender isn't specified, even during the cutscene taking place after the battle. It's possible that it's female, however, as the narrator in the ending refers to it as "the Mother of Harlots".
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* BossBanter: It speaks scripture in a deep voice when performing its laser beam attack. Once it reaches its second form, the music is accompanied by a bombastic hellfire and brimstone preacher speaking the word of God.
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-> Debut: ''Antibirth''[[note: as The Witness]]
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-> Debut: ''Antibirth''[[note: as ''Antibirth''[[note]]as The Witness]]Witness[[/note]]
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-> Debut: ''Repentance''
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-> Debut: ''Repentance''''Antibirth''[[note: as The Witness]]
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* SmallRoleBigImpact: Is only the subject of one relatively short boss fight, but its influence on Isaac's life is far-reaching.
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* ThirdEye: One of its attacks in its first form has it fire a barrage of Godhead bullets. Indeed, Dogma has a third eye while using this attack, just like Isaac does with Godhead.
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* AngelicAbomination: Its secondary form, which resembles an ophanim.
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* AngelicAbomination: Its secondary form, which resembles an ophanim.[[https://en.wikipedia.org/wiki/Ophanim ophanim]].
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One of two bosses of TheVeryDefinitivelyFinalDungeon, Home.
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One of two bosses of TheVeryDefinitivelyFinalDungeon, TheVeryDefinitelyFinalDungeon, Home.
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One of two bosses of TheVeryDefinitiveFinalDungeon, Home.
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One of two bosses of TheVeryDefinitiveFinalDungeon, TheVeryDefinitivelyFinalDungeon, Home.
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One of two bosses of TheVeryDefinitiveFinalDungeon, Home.
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* AmbiguousGender: The beast's gender isn't specified, even during the cutscene taking place after the battle.
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Dogma is easily my favorite boss in Isaac, due to its themes and how important it is to Isaac's story. It's arguably the most important boss in the entire Isaac canon, next to Mom herself. Also I don't know what to do with The Beast, if anybody else wants to help with that I'd love it.
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!!Dogma
-> Debut: ''Repentance''
-> Floor(s): Home
After a flashback sequence where Isaac recalls the fallout between his parents' relationship, he has a nightmare about the televangelist sermons that drove his mother to madness.
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-> Debut: ''Repentance''
-> Floor(s): Home
After a flashback sequence where Isaac recalls the fallout between his parents' relationship, he has a nightmare about the televangelist sermons that drove his mother to madness.
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* GreaterScopeVillain: Dogma is the personification of the demented fundamentalism which led to Mom's descent into religious madness. It's essentially the source behind all of the negative influence that Christianity had on Isaac, and is thus a significant contributor to Mom's antagonism.
* LightIsNotGood: ''Far'' from it. It's the only boss whose versus splash art has a bright white background, as opposed to the darkness of every other boss; it's the only source of light in its arena; and the preacher's ranting about "God's Light" is one of the biggest sources of conflict in Isaac's life.
* LightIsNotGood: ''Far'' from it. It's the only boss whose versus splash art has a bright white background, as opposed to the darkness of every other boss; it's the only source of light in its arena; and the preacher's ranting about "God's Light" is one of the biggest sources of conflict in Isaac's life.
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----
!!The Beast
-> Debut: ''Repentance''
-> Floor(s): Home
The Beast of the Apocalypse, heralded by the Four Horsemen. Repentance's TrueFinalBoss (for real this time), The Beast challenges Isaac after his victory over Dogma.
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!!The Beast
-> Debut: ''Repentance''
-> Floor(s): Home
The Beast of the Apocalypse, heralded by the Four Horsemen. Repentance's TrueFinalBoss (for real this time), The Beast challenges Isaac after his victory over Dogma.
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* FireAndBrimstoneHell: As a stark contrast to Sheol, The Beast's lair is a fiery cavern flooded with lava.
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%%
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%% NOTE TO EDITORS: NEVER put spoiler tags in folder titles or the description of characters above the list of trope examples. Ever. NEVER put the name of a trope at the beginning of a trope entry in spoiler tags. Ever. Don't put spoilers in the descriptions at the beginning of the list of examples at all. If the trope name on its own is a spoiler, either don't add an entry for it at all or embed it as a pothole from another example. Read Administrivia/HandlingSpoilers for further details.
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%% FURTHER NOTE TO EDITORS: Trope entries NEVER get second-level bullets. Ever. Not even below relevant supertropes - many tropes have multiple supertropes anyway. If you are adding a trope entry as a sub-bullet under another trope, stop. Put the trope in its correct place alphabetically, as a FIRST-level bullet. See Administrivia/ExampleIndentationInTropeLists for details.
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%% NOTE TO EDITORS: NEVER put spoiler tags in folder titles or the description of characters above the list of trope examples. Ever. NEVER put the name of a trope at the beginning of a trope entry in spoiler tags. Ever. Don't put spoilers in the descriptions at the beginning of the list of examples at all. If the trope name on its own is a spoiler, either don't add an entry for it at all or embed it as a pothole from another example. Read Administrivia/HandlingSpoilers for further details.
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%% FURTHER NOTE TO EDITORS: Trope entries NEVER get second-level bullets. Ever. Not even below relevant supertropes - many tropes have multiple supertropes anyway. If you are adding a trope entry as a sub-bullet under another trope, stop. Put the trope in its correct place alphabetically, as a FIRST-level bullet. See Administrivia/ExampleIndentationInTropeLists for details.
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[[WMG:[[center: [- ''VideoGame/TheBindingOfIsaac'' '''[[Characters/TheBindingOfIsaac Main Character Index]]'''\\
[[Characters/TheBindingOfIsaacMainCast Main Cast]] | Monsters ([[Characters/TheBindingOfIsaacEnemies Enemies]] | [[Characters/TheBindingOfIsaacBosses Bosses]] | '''Final Bosses''')]] -]]]
[[Characters/TheBindingOfIsaacMainCast Main Cast]] | Monsters ([[Characters/TheBindingOfIsaacEnemies Enemies]] | [[Characters/TheBindingOfIsaacBosses Bosses]] | '''Final Bosses''')]] -]]]
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!!Final Bosses
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!!Final Bosses
Yes, boss''[[SerialEscalation es]]''. Your very first playthrough will end at Depths II with you killing Mom, but as you beat the game repeatedly, you unlock more chapters, each with a FinalBoss bigger and tougher than before.
All spoilers are unmarked from here on out. Proceed at your own caution!
[[folder:Mom]]
!!Mom
[[quoteright:141:https://static.tvtropes.org/pmwiki/pub/images/momleg.png]]
->Debut: ''The Binding of Isaac''
->Floor(s): The Depths, Necroplis, Dank Depths
At the end of the Depths, Isaac finally confronts his mother. As her foot stomps down on Isaac from above, she looks and sends her hands through the doors of the boss room while spawning enemies. But even if Isaac defeats Mom, it's not the end.
----
* AttackOfTheFiftyFootWhatever: Her boss fight.
* AxCrazy: Her goal is to kill her own son, and she doesn't sound too upset about it during the fight, what with the laughing and all.
* BattleThemeMusic:
** The original game had "''[[https://www.youtube.com/watch?v=_q9ZC-UwViM Thine Wrath...]]''", an orchestrated theme that sounds nearly angelic at points while still being dreadful, to symbolize Mom's willingness to kill her own son to appease what she perceives as "God".
** ''Rebirth'' gave her "''[[https://www.youtube.com/watch?v=EBJEHIxHuKE Matricide]]''", which leans more to heavy rock and an oppressive tone backed up by a choir.
* BodyHorror: The way Mom's body parts move throughout the fight (such as both eyes appearing on opposite sides of the room while she tries to stomp on you) suggest an ability to contort herself in rather...impossible ways.
* BossBanter: ''ISAAAAAC!''
* DeathByIrony: Crushed by her own bible!
* DiscOneFinalBoss: Demoted to this on your second playthrough and beyond.
* EvilIsVisceral: Likely the reason her body parts are detailed and somewhat deformed.
* EvilLaugh: She lets out one every time she successfully damages Isaac.
* EvilMatriarch: A monstrous final boss in the form of Isaac's mother.
* TheFaceless: Her entire face is never shown at any point in the main game (the intro and epilogue don't count, as they're Isaac's cartoon drawings). This is [[SubvertedTrope subverted]] after you beat the Chest in ''WOTL'' or ''Rebirth'', but only briefly. In photographs, to be precise.
* FanDisservice: When Isaac uses the Mom's Bra item, a picture of his mother's shirtless torso flashes on the screen. A ''very'' unflattering picture of his mother's less-than-fit shirtless torso.
* FatBastard: As shown by her giant leg and the picture that shows up when using Mom's Bra.
* FinalBoss: In your first playthrough. She's nowhere near the TrueFinalBoss, though.
* FlunkyBoss: She'll summon groups of random enemies to battle Isaac.
* GameplayAndStoryIntegration: Using the Bible instantly defeats her in her boss fight.
* GiantFootOfStomping: Her main method of direct attack.
* {{Gonk}}: See that leg up above? That's all the proof you need.
* GrossUpCloseUp: One of her leg in the boss portrait, and one of her body in the picture that appears when using Mom's Bra.
* HumanoidAbomination: Most of what she does in-game and in a few cutscenes blatantly disregards normal body movements if not physics. She can step on her own eye, generally alter her size, and her arm can fit in a chest inside her heart inside her womb.
* MookMaker: Spawns an array of previous enemies to make her battle harder. She does it from her body fat, which almost pours out of the boss room doors.
* MotherOfAThousandYoung: If you go by the theory that the majority of the enemies are her former children.
* SayMyName: ISAAC!
* SkippableBoss: Provided you have the Bible on you by the time you reach her, and it's fully charged.
* TacticalSuicideBoss: It's not actually mandatory, but making her stomp herself is possible and deals lots of damage.
* VoiceOfTheLegion: Her dialogue consists of her screaming "Isaac" in a demonic voice.
* WombLevel: After defeating her, you will unlock her womb as a playable level.
* YourSizeMayVary: Just how big is she? In the cutscenes, she's a normal-sized human being, but her underwear is the right size to be worn by a child visibly smaller than her, in the boss fight her leg is the length of the screen, and then her womb is big enough to have two entire levels in it, with her heart being larger than Isaac.
[[/folder]]
[[folder:Mom's Heart/It Lives!]]
!!Mom's Heart/It Lives!
[[quoteright:147:https://static.tvtropes.org/pmwiki/pub/images/momsheart.png]]
[[quoteright:103:https://static.tvtropes.org/pmwiki/pub/images/itlives.png]]
->Debut: ''The Binding of Isaac''
->Floor(s): The Womb, Utero, Scarred Womb
Defeating Mom once unlocks the Womb in subsequent playthroughs. At the end of the Womb lies Mom's Heart, which, summons enemies like Mom does. Defeating Mom's Heart reveals a Chest with something special inside. But once it's beaten enough times, it will become "It Lives!", which is Isaac as a fetus for some odd reason.
----
* BattleThemeMusic:
** "''[[https://www.youtube.com/watch?v=Zj9Ck3mNP4o ...Be Done]]''" in the original, completing Mom's theme and serving as a fast-paced theme to match the intensity of the fight.
** "''[[https://www.youtube.com/watch?v=eCW3hHhN8V4 Ventricide]]''" in ''Rebirth'', echoing Mom's theme in leaning more towards darker guitar and pounding drums with a background choir, sounding far more sinister. The term "ventricide" in itself isn't real, but it would roughly signify "death of the womb", and could be seen as a {{Pun}} on "ventricle".
* BossBanter: Has the same voice lines as Mom, only muffled.
* BossRush: It Lives has the ability to spawn {{Degraded Boss}}es such as Monstro, Larry Jr., and Chub to fight you alongside the enemies.
* BulletHell: ''Rebirth''[='=]s version shoots red tears nearly constantly throughout the whole fight, even when retreating to the back of the room.
* TheBusCameBack: The original Mom's Heart form, to an extent, in ''Afterbirth†''. While unlocking It Lives used to make it so that you can no longer fight Mom's Heart, ''Afterbirth†'' lets you fight Mom's Heart again in the Void, likely so that the Bestiary is completable for those who already unlocked It Lives. It also shows up as a possible boss encounter in the Womb stage of Greed mode.
* DamageSpongeBoss: Its lack of mobility is made up for by a big health bar. Its Eternal version in the ''Eternal Edition'' has ''even more''.
* FetusTerrible: It Lives is not just any embryo, it has been confirmed by WordOfGod to be Isaac's embryo.
* FlunkyBoss: Will summon enemies intermittently. It Lives ups the ante by spawning {{Degraded Boss}}es.
* GetBackHereBoss: Despite not moving, it accomplishes this by occasionally retreating above the screen and leaving you to deal with its flunkies for a while.
* MookMaker: Hides at the back of the room while it spawns normal enemies to fight you, then jumps back to the centre to spawn more.
* NotQuiteDead: It seems that Mom survived their fight, or at least her heart did.
* SkippableBoss: Using the Bible instantly kills it like it did with Mom.
* StationaryBoss:
** In the main game, all it can do movement-wise is pull itself upwards to hide from attacks, making bombs very useful against it.
** The Eternal form in the ''Eternal Edition'' averts this greatly; it will pursue you relentlessly around the room until it dies, still spawning enemies.
* TacticalSuicideBoss: In ''Rebirth'', it moves to the top of the screen instead of disappearing entirely. Anything that wanders up there, enemies included, takes damage.
* TrueFinalBoss: Was initially this to Mom's FinalBoss. However, this is subverted by the Halloween update, and further subverted by ''Wrath of the Lamb'' and ''Rebirth'', to the point that it's no longer anywhere ''near'' the real final boss.
[[/folder]]
[[folder:Satan]]
!!Satan
[[quoteright:144:https://static.tvtropes.org/pmwiki/pub/images/satan.png]]
->Debut: ''The Binding of Isaac''
->Floor(s): Sheol
The original TrueFinalBoss (although this isn't true as of ''Wrath of the Lamb'' and ''Rebirth''), Satan himself is the boss of what was originally the game's secret floor. Despite offering [[DealWithTheDevil Deals with the Devil]] throughout the game, he turns on Isaac and tries to kill him. His boss fight is comprised of three phases, detailed below under SequentialBoss.
----
* AttackOfTheFiftyFootWhatever: His final form is him flying far above the screen and stomping on Isaac with giant feet a la the Mom boss fight.
* BattleThemeMusic:
** "''[[https://www.youtube.com/watch?v=PhMj9tMtRs8 Enmity of the Dark Lord]]''" in ''Wrath of the Lamb'', an epic-sounding theme with techno and bells, along with heavy emphasis on bass.
** "''[[https://www.youtube.com/watch?v=Yq01zDqEOec Hericide]]''" in ''Rebirth'', a theme with heavier guitar and OminousLatinChanting, along with a deep voice growling demonically. "Hericide" roughly means "death of the master/teacher/lord".
* BlackSpeech: During the fight with him, he sounds somewhat like this. They are actually Mom's quotes, played backwards and in a much lower tone.
* DealWithTheDevil: He offers them throughout the game before you reach Sheol. Possibly even as you reach Sheol or after, if you have a Joker card on hand.
* EnergyWeapon: His second phase can fire dual Brimstone lasers from his hands (that can curve), or a single one from [[BreathWeapon his mouth]].
* EvilLaugh: Since he uses Mom's voice clips, he can do this.
* FaustianRebellion: Even if you do a ton of deals with him, you can still kill him (and the power ups from said deals can make it all the easier).
* FlunkyBoss: His first form is spawning the Fallen to fight you instead. His third phase continuously spawns Kamikaze Leeches.
* GiantFootOfStomping: His third phase has him attempting to crush Isaac with his giant hooves. They work like Mom's, but he does it much faster.
* LivingStatue: His second form is a unique boss where the statue of Satan comes to life, grows much larger, and attacks Isaac with tears and lasers.
* TheManBehindTheMan: Implied; after all, he did at the very least string Isaac along through the [[DealWithTheDevil Deals]] he makes in the devil rooms earlier on, before turning on Isaac at the last minute.
* {{Nerf}}: Satan's legs in his third phase no longer deal contact damage in ''Rebirth''.
* OneWingedAngel: After defeating his first form, he grows to massive size and attempts to stomp on you.
* PressXToDie: Using the Bible on him, which killed Mom and Mom's Heart instantly, kills ''you'' instantly instead.
* {{Satan}}: It's in his name, and he looks the part as well.
* SayMyName: Satan's battle cry when you defeat his first phase is Mom's BossBanter, only lower pitched and in reverse.
* SequentialBoss: Three phases: first a fight with The Fallen, then a fight with Satan himself on the ground with you, and finally a fight against his giant stomping legs.
* TacticalSuicideBoss: Those leeches he spawns don't just hurt Isaac.
* ThemeMusicPowerUp: When you fight the Fallen, his first phase, the regular boss theme plays. When Satan actually starts fighting, however, Hericide kicks in.
* TrueFinalBoss: He was the final boss of the game in the Halloween update, but this was trumped by ''Wrath of the Lamb'' and has just gotten further and further from the truth as more content has been added.
[[/folder]]
[[folder:Isaac]]
!!Isaac
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/isaacboss.png]]
->Debut: ''Wrath of the Lamb''
->Floor(s): Cathedral
After beating It Lives, the Cathedral is unlocked. At the end of the Cathedral resides Isaac himself.
----
* AscendToAHigherPlaneOfExistence: Appears to do this upon his defeat.
* BaldOfEvil: Justified, being a young child and all.
* BattleThemeMusic:
** The original game had "''[[https://www.youtube.com/watch?v=H4noeZx9W6s My Innermost Apocalypse]]''", a techno-rock theme that involves a [[BossRemix sad reprise of the title screen music]].
** ''Rebirth'' gave him "''[[https://www.youtube.com/watch?v=Fr2BzEgwBwM Infanticide]]''", which is entirely centered around an OminousLatinChanting and heavy guitar, with the version in-game adding a OneWomanWail.
* BeamSpam: One of his attacks in ''Rebirth'' has him covering most of the room with beams of light, except for a couple safe spots in the corners. His third phase in old versions of ''Wrath of the Lamb'' had no attacks other than rapidly dropping the beams on random spots in the room.
* BoltOfDivineRetribution: Like Conquest, he can summon several pillars of light. The safe spot is in either corner of the room perpendicular to the direction the pillars are spawning.
* BulletHell: Fires bullets in all directions, and fires at you if you hit him. Having a high-fire rate can backfire horribly.
* ChildrenForcedToKill: A subtle example. While it's easy to miss, Isaac doesn't attack at all until he takes damage.
* CounterAttack: In addition to the projectiles he fires periodically, he also fires at you whenever you damage him. In ''Rebirth'', he constantly fires in your general direction when not using another attack, instead of only doing so when hit.
* DamageSpongeBoss: Later updates in ''Wrath of the Lamb'' made him this. ''Rebirth'' instead adds more BulletHell, and makes him mobile in his third form.
* EnemyWithout: Maybe.
* [[EvilCounterpart Evil Counterpart/Good Counterpart]]:
** He seems to be the latter to Satan. He appears in a Cathedral instead of Sheol, summons angels instead of demons, and has an angelic appearance.
** He could qualify as either to the PlayerCharacter. The fight against him is most likely more symbolic than literal anyway.
* FlunkyBoss: Spawns Angelic Babies, which is fitting.
* GoOutWithASmile: Well, he is smiling in his third phase.
* HolyHandGrenade: He can cover the screen in rays of deadly light.
* MessianicArchetype: His OneWingedAngel.
* MirrorMatch: He ''is'' Isaac. Note that he's not a MirrorBoss, as he can do things you'll never be able to pull off.
* PowerGivesYouWings: In his final form. An item called Fate can be unlocked, allowing the player to have those same wings.
* PurposefullyOverpowered: You know how almost all the items added to ''Wrath of the Lamb'' are much more powerful than the ones in the base game? ''There's a reason for that.''
* SequentialBoss: Three phases: one lying in the fetal position, one standing up, and one with wings and teleportation.
* StationaryBoss: For the original game and the first two phases in ''Rebirth''.
* TroubledFetalPosition: The first part of the fight.
[[/folder]]
[[folder:???]]
!!???
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/bluebabyboss.png]]
->Debut: ''Wrath of the Lamb''
->Floor(s): The Chest
Completing the Cathedral with the Polaroid item allows Isaac to enter The Chest. At the end of this super-secret stage lies...the Blue Baby?
----
* BackFromTheDead: Is a post-mortem version of Isaac, naturally.
* BattleThemeMusic: While the original version of the fight in ''Wrath of the Lamb'' shared "''My Innermost Apocalypse''" with Isaac, ''Rebirth'' gave him a proper, original theme called "''[[https://www.youtube.com/watch?v=FT3sXT9x9CU Ascension]]''", which has discernible Latin lyrics and an aggressive rock beat with odd, creepy noises in the background at certain points.
* TheCameo: From Creator/EdmundMcMillen's flash series ''Dead Babies''.
* DivergentCharacterEvolution: In ''Wrath of the Lamb'', ??? was mostly an Isaac clone right down to having the same boss theme, with the only real differences being his ability to spawn flies and periodically shoot homing tears. ''Rebirth'' reworked both bosses, and ??? was thus given a more distinctive pattern, most noticeably removing the beams of light in favor of increasing the rate at which he spawns flies, and a unique boss theme. The distinction is most obvious in their reworked final phases: Isaac prefers to [[GetBackHereBoss fly away from the player]] at high speed while periodically teleporting away to saturate the room with beams of light, while ??? slowly flies towards the player while spawning flies and Pooters and occasionally teleporting into the player's face.
* FlunkyBoss: One way he varies from the previous boss is that he summons flies in addition to his other attacks.
* InvincibleMinorMinion: In ''Rebirth'', he gets a halo of flies, which block your tears.
* OrbitingParticleShield: ''Rebirth'' gives him two Eternal Flies to block tears partway through the fight. He also gains the ability to summon Pooters, which orbit him at high speed and can thus serve as shields in addition to attacking the player.
* PaletteSwap: He is very similar to the previous boss, Isaac, so most of the tropes above apply to him too. This resemblance is downplayed in ''Rebirth'' by giving him different attack patterns from Isaac.
* TeleportSpam: Utilized in his third phase in ''Rebirth'', with a tendency to reappear [[TeleFrag right on top of the player]].
* TrueFinalBoss: Of ''Wrath of the Lamb'', being the boss of the only sixth chapter in the game, and since beating him unlocked the game's real ending. Subverted in ''Rebirth''.
* WeaponizedTeleportation: Tries to teleport into the player during his third phase in ''Rebirth''.
[[/folder]]
[[folder:The Lamb]]
!!The Lamb
[[quoteright:169:https://static.tvtropes.org/pmwiki/pub/images/lamb.png]]
->Debut: ''Rebirth''
->Floor(s): Dark Room
Defeating Satan and completing Sheol with the Negative item allows Isaac to enter The Dark Room, a dark reflection of The Chest. The skeletal demon known as the Lamb is the boss of this stage, and it fights with powerful attacks.
----
* AllYourPowersCombined: The Lamb's volleys of shots mirror those of previous bosses. This, combined with how it switches the type of bullet with each volley, and that all of its bullets are the same colour, make it a very difficult opponent to predict.
* TheAntiChrist: In the Bible, the Lamb was a symbolic reference to Jesus. In this game, however, the Lamb is an undead demonic creature fought after Satan. The implication is that this Lamb is an alternate, [[SatanicArchetype demonic interpretation]] of Jesus.
* BattleThemeMusic: "''[[https://www.youtube.com/watch?v=DWo3PQjxogQ&t=107s The Fallen Angel]]''", a dark, creepy, fast-paced song with an ominous choir and wail.
* BlackoutBasement: When the body on his second phase is defeated, the room will darken for a brief time.
* CreepyCoolCrosses: Specifically, an upside-down one on his forehead.
* DemBones: The Lamb is essentially a demonic skeletal child with curved horns.
* DetachmentCombat: His second form involves his head floating around the room attacking you while his body lies limply on the ground spawning flies and sometimes tossing out Monstro-style shots.
* DualBoss: His second form, in which his head floats around the arena and his body stays on the ground to summon Flies and fire off a burst of tears.
* EnergyWeapon: His second form gains the ability to shoot four-way Brimstone in the cardinal directions. He can also start rotating the beams like Mom's Heart/It Lives.
* FlashStep: One of his attacks qualifies as this.
* HornedHumanoid SkullForAHead: He looks like an undead demon.
* LosingYourHead: During the second phase of the battle.
* MythologyGag: His name is a reference to the expansion for the original Isaac, named ''Wrath of the Lamb''. He is also visually similar to ''Wrath of the Lamb's'' horned skull logo. Given that Edmund had more planned for the original ''Isaac'', it's possible he was always intended to be the last boss of the expansion, but Flash's limitations meant he couldn't add him in.
* NightmareFace: Its skeletal face isn't pleasing to look at, especially in the vs. screen.
* OffModel: The Lamb's portrait in the versus screen is dark in color, but in-game and in the ''Afterbirth†'' trailer, The Lamb is coloured white.
* SequentialBoss: Has two forms, first as one entity then split into a DualBoss with its head and body.
* ShadowArchetype: In addition to mirroring other bosses, The Lamb's attacks also resemble combinations that can be used by Isaac -- for example, Monstro's Lung plus Homing Tears. Its DetachmentCombat is a lot like the Pinking Shears. It even begins the battle in Isaac's crying position!
[[/folder]]
[[folder:Mega Satan]]
!!Mega Satan
[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/theres_two_of_them.png]]
->Debut: ''Rebirth''
->Floor(s): The Chest, Dark Room
In ''Rebirth'', a giant golden door appears in the Chest and Dark Room stages. This door can be unlocked with a special item, which leads to ''Rebirth''[='=]s ultimate boss battle.
----
* AttackOfTheFiftyFootWhatever: Although the name probably gave it away.
* BattleThemeMusic: Shares "''Hericide''" with his own original form.
* BossRush: He summons bosses as he takes damage, and more if you don't do enough damage fast enough.
* BraggingRightsReward: Besides unlocking the final and definitive ending, there is no reason to fight him other than to boast you did it. The only thing you get out of winning is a new picture for your save file. There are no associated items or character unlocks, not even a mark on the character file to indicate that character beat him. This has since been [[AvertedTrope averted]] with ''Afterbirth'', as he now has his own completion mark with unlocks tied to it, in addition to counting towards the co-op baby (or Godhead, in The Lost's case) unlocked by getting all completion marks for a character on hard mode, '''and''' beating him once with every character unlocks the Mega Blast item. ''Afterbirth†'' adds another with Booster Pack 5, where defeating him once now unlocks Apollyon.
* BulletHell: What some of his attacks delve into. In his second phase, it's his ''only'' form of attack, albeit in several varieties.
* CognizantLimbs: His hands.
* DamageSpongeBoss: He's just shy of Hush in terms of overall health, and his individual forms have as much or more health than any other boss save Ultra Greed. He could actually be considered to have more health than any boss if you include the health of the mandatory boss fights. However, Mega Satan doesn't have the same damage-scaling property of those two, so he's functionally a whole lot weaker than they are.
* DemBones: Transitions from flesh and bone to just bone once he's in his second phase.
* FinalBossPreview: Regular Satan's third phase can be considered this. In Sheol, you only fight his lower half. In the Chest/Dark Room's secret room, you face the much more difficult upper half.
* FlunkyBoss: Summons The Harbingers, the Super Sins, and fallen versions of the Angels. If you take too long on one of his phases, he starts summoning regular Sins... [[TheLastOfTheseIsNotLikeTheOthers and The Hollow]].
* GiantHandsOfDoom: Accompanied by a giant head. The hands serve mainly to [[ShieldedCoreBoss block shots aimed at the head]], which is treated as the main boss. Destroying the hands will cause a set amount of damage to be dealt to the main head, and the hands [[DidntNeedThoseAnyway disappear once the second phase begins]].
* GuideDangIt: The only in-game hint you have to his existence is "The Angels await!" You're supposed to bomb the Angel statues in the Angel Rooms, prompting them to engage you; both will drop a piece of a Golden Key on defeat, and getting both pieces opens a Golden Door in the Chest/Dark Room that leads to Mega Satan.[[note]]The Golden Door also only appears once you have completed the key for the first time, which is a GuideDangIt in and of itself.[[/note]] Fortunately, completing the key also unlocks "Dad's Key" as a regular item, which can also be used on the Golden Door for future playthroughs [[note]]The "Get Out of Jail Free" card also works[[/note]].
* InterfaceScrew: The only boss [[note]]Besides the Mask Of Infamy in the original[[/note]] who doesn't have a health bar, in either form. Averted if you have the Spider Mod item, which gives him a Spider Mod health bar.
* MarathonBoss: He has two forms, each of which has as much if not more health than every other boss excluding Hush and Ultra Greed. This is on top of all the other bosses he summons. Winning takes several minutes at least, and that's if you have a good enough run.
* RedEyesTakeWarning: Considering he was the TrueFinalBoss of the game before the title was being uplifted by Delirium, you ''will'' want to take warning.
* SealedEvilInACan: Heavily implied to be sealed by the beings in the Angel Rooms.
* SequentialBoss: Including his summons, he has ''twelve'' phases.
* ShowsDamage: While not present in the first phase, cracks will start to form across Mega Satan's skull; starting with a few cracks after some damage has been done and several more appearing once some serious damage has been dealt.
* SoundtrackDissonance: Due to a bug, doing too much damage to any form will cause the calm, somber "boss defeated" music to start playing. This was eventually patched.
* TrueFinalBoss: The second to last True Final Boss of the game (which is saying something, considering there have been ''seven other candidates'' before it), hidden at the final stage and having an extra unlock process required each run. Delirium took over the role in ''Afterbirth†'', but even then it is the final boss of an alternate route that also has a 50% chance of being available from Mega Satan.
* TurnsRed: Has two full health bars, and when you take down one of them, he really cranks up the BulletHell.
* WaveMotionGun: If you stand in front of him for too long, he'll charge up a gigantic blood laser for a long time, making his head nigh-impossible to shoot.
[[/folder]]
[[folder:Hush]]
!!Hush
[[quoteright:185:https://static.tvtropes.org/pmwiki/pub/images/hush.png]]
->Debut: ''Afterbirth''
->Floor(s): ???
Defeating Mom's Heart or It Lives in under thirty minutes of total play time unlocks a short, hidden area[[note]]displayed as ??? in-game but generally called the Blue Womb or Dead Womb[[/note]]. This area only has one enemy: Hush, which appears to be another PaletteSwap of the Isaac and ??? bosses. Then he enters his ''second'' form, which is soundly described below.
----
* AttackOfTheFiftyFootWhatever: According to Edmund, it's a giant ??? pushing through the floor.
* BattleThemeMusic: Its first phase shares "''Ascension''" with ??? (because according to Edmund, it ''is'' ???), before it transitions to the heavier and oppressive "''[[https://www.youtube.com/watch?v=rbflsmpA69c Morituros]]''" when Hush's true form emerges.
* BodyHorror: Hush represents Isaac suffocating inside the chest; unsurprisingly, its "face" looks like it's being asphyxiated inside a bag.
* BonusBoss: Hush is sort of the "Isaac" counterpart to Mega Satan. While beating it does grant you a new ending, it doesn't require you to end the game. Instead, you can opt to go to Sheol/Cathedral once the fight is over. This was later patched out; defeating Hush now plays the ending and ends the run, but only the first time you beat it.
** Averted as of ''Afterbirth†''; beating Hush is the only guaranteed way to reach the Void and fight [[TrueFinalBoss Delirium]], and is required to actually unlock the Void.
* BulletHell: Its attack patterns during its second form. They even resemble the dense ring-patterns found in ''danmaku'' shooters like the ''Franchise/TouhouProject'' games; fortunately, the projectiles fired by these attacks are some of the slowest in the game.
* DamageSpongeBoss: Has the second highest health of all bosses in the game. Furthermore, its defenses scale with your damage output, so no matter what items you have, it'll take a long time to wear down. Combine this with its numerous BulletHell attacks and absurd enemy spawns, and you have a brutal boss fight.
* EldritchAbomination: As an embodiment of impending death by suffocation that looks like a giant face molded from blue flesh.
* FlunkyBoss: Begins spawning hordes and hordes of minions as the battle goes on.
* MarathonBoss: Hush has 6666 health and has a damage resistance mechanic which hardcaps how much damage you can do at once. Even an overpowered build will still take ten minutes to kill this thing.
* MeaningfulName: To hush is "to put at rest", and seeing as this boss represents Isaac slowly suffocating in the Chest, the name is ''quite'' appropriate.
* NumberOfTheBeast: Its base HP is 6666.
* OcularGushers: When low on health, Hush will fire out geyser-like streams of tears from its eyes that track you like a pair of KillSat [[EnergyWeapon lasers]].
* SequentialBoss: Fights like Isaac and ??? at first, but then it teleports away and its huge face comes out of the floor, firing loads of bullets.
* StationaryBoss: Mostly. It begins laying on the ground, as a variant of Isaac and ???, then turns into a large bullet-spewing head. The head can move around, but generally, it stays still when attacking.
* SuspiciousVideoGameGenerosity: Before the fight, the game gives you two item rooms, four golden chests, and a shop. Needless to say, ''you will need them''.
* ThemeMusicPowerUp: The first phase of the fight has ''Ascension'' playing in the background. Once the second phase begins, the music changes to Hush's own theme, ''Morituros''.
* TrickBoss: Shares a boss theme with ??? and fights like him, with a health bar that goes all the way down to zero, so you'd think that's all there is to him. Nope.
* WrapAround: It fires shots that go out of the room and then come back from the other side. Notably, these shots actually get ''faster'' after the wrap-around.
* ZergRush: Easily spawns more enemies than any other boss in the game, throwing entire floors' worth of flies, Gapers, and Boils at you throughout the fight.
[[/folder]]
[[folder:Ultra Greed/Ultra Greedier]]
!!Ultra Greed/Ultra Greedier
[[quoteright:161:https://static.tvtropes.org/pmwiki/pub/images/ultra_greed.png]]
[[quoteright:160:https://static.tvtropes.org/pmwiki/pub/images/ultra_greedier.png]]
->Debut: ''Afterbirth'' (Ultra Greed)\\
''Afterbirth†'' (Ultra Greedier)
The final boss of Greed Mode fought in a stage named after him. A giant version of Greed that uses coins to attack, summon minions or heal. ''And he still makes you drop money when hit''.
----
* AnimationBump: Ultra Greed moves around a ''lot'', and the animations are ''extremely'' smooth and detailed.
* AttackOfTheFiftyFootWhatever: A massive variant of Greed.
* BanditMook: Like his smaller versions, his attacks will cause you to drop money. Unlike the others, however, he will actively pick up the money you drop, which heals him slightly.
* BossRemix: "''[[https://www.youtube.com/watch?v=mhdlLlRMH_c Chorus Mortis]]''". It incorporates elements of the shop and arcade themes, the latter of which is, itself, a remix of the title screen.
* CripplingOverspecialization: Ultra Greedier uses almost nothing but explosive attacks. With Pyromaniac or the Host Hat, he is literally incapable of harming you outside of contact damage and highly telegraphed lasers.
* DamageSpongeBoss: His health is slightly higher than that of Mega Satan's first form, making him third overall, and the damage scaling means he'll last a whole lot longer.
* DefendCommand: One of his abilities is to shield himself with his arms, reducing all damage dealt to him, which he usually uses when he has flunkies or bomb coins active.
* EnergyWeapon: In his second form, the doors shoot gold Brimstone beams whenever he pounds the ground.
* FanDisservice: [[https://bindingofisaacrebirth.gamepedia.com/File:Boss_Ultra_Greed_back.png Has a large, visible, and well-detailed butt]]. He's also a massive corpse-like monster that ultimately has a little boy as the base of his design, and might even ''be'' an alternate version of a little boy.
* FinalBoss: Of Greed Mode.
* FlunkyBoss: Can spawn Keepers close to himself, call more minions from the arena's doors, and drop a bunch of large coins that will cast buffs on him if they're not destroyed.
* TheGambler: His primary attack depends on the outcome of a slot machine. Although it's not ''that'' much of a gamble since every outcome is pretty terrible for you. You're just hoping that he gets one of the ''less'' terrible ones.
* KingMook: To Greed and all of his mook counterparts.
* MadBomber: One of his slot machine attacks is to drop giant bomb coins all over the arena. Ultra Greedier gains an explosive effect on all of his attacks.
* MarathonBoss: His health is about half that of Hush, but he shares the same damage reduction mechanic to prevent you from winning too fast. Furthermore, he has the ability to heal during the fight, though not by much. Greedier Mode is even worse, as there's the second half to his fight.
* MoneyToThrowAway: Uses large coins as projectiles. At times, huge ones fall from above. They can explode, heal Ultra Greed, or allow him to summon minions if you don't get rid of them.
* NoCureForEvil: A notable aversion. He's unique in his ability to heal through heart coins, though it isn't very much. He'll also heal a little if he picks up the coins you drop.
* NooseNecktie: Like all other versions of Greed. The main difference being that you get to see Ultra Greed snap it loose himself.
* PaletteSwap: Ultra Greedier, Ultra Greed's gold-colored form.
* SequentialBoss: In ''Afterbirth†'', he becomes this in Greedier Mode. After beating his first form, his statue (now called Ultra Greedier) will start attacking.
* SpinAttack: Does spinning lariats when you're close.
* StoneWall: His attacks, unlike most other final bosses, don't employ BulletHell and are comparatively easy to avoid. He makes up for this by being able to tank attacks that only Hush could withstand, with his damage reduction ensuring that he will always last for a few minutes. The challenge comes not from dodging him, but from ''outlasting'' him.
* TacticalSuicideBoss: Downplayed compared to most examples, but his bomb coins can damage him as well. He uses his DefendCommand to block most of the damage. His second form is even worse in this regard since all of his attacks have explosive properties and he no longer defends. Half of the time you won't land the final hit that kills him.
* TakenForGranite: Ultra Greed turns into a solid gold statue when killed. Midas' Touch (touched enemies temporarily turn into gold) applies a penalty to his damage scaling property, letting you deal greatly increased damage. In Greedier Mode, he keeps attacking as a statue and explodes into a fine gold dust on death.
* TurnsRed: As he loses health, his attacks become faster and he spawns more giant coins, which also take effect more quickly. He also visually becomes redder as an indication of this. He also does this whenever heals via the Heart Coins from his slot machine or by picking up coins; the more he heals, the redder he gets. This is only temporary, however.
* YourPrincessIsInAnotherCastle: On your first run through Greedier Mode. So you've beaten Ultra Greed, he's turned to a statue, and you wait for the Greed Machine to spawn... but it doesn't, and after a long pause, Ultra Greed's statue starts attacking you. This new form is appropriately called Ultra Greedier. He doesn't bother with the pretense on subsequent runs and will begin attacking in his statue form almost immediately.
[[/folder]]
[[folder:Delirium]]
!!Delirium
[[quoteright:192:https://static.tvtropes.org/pmwiki/pub/images/portrait_delirium.png]]
->Debut: ''Afterbirth†''
->Floor(s): The Void
The penultimate final boss of the entire game, added in ''Afterbirth†''. Beating Hush will unlock The Void, made up of various different environments from the game, with this as the boss of one of its several boss rooms. It first appears to be a giant, melting skull, but will shift forms to white variations of the previous bosses.
----
* AmbiguousGender: Being less of a "person" and more of a manifestation of a mental breakdown that can change into almost any other boss from the game that takes the form of a gigantic skull, it's difficult to tell if Delirium even has a gender in the first place. A Tweet from Edmund [=McMillen=] during the promotion of ''Four Souls'' refers to Delirium with "him", however.
* AllYourPowersCombined: This is the boss' primary attack method. It will randomly transform into almost any other boss found throughout the game (including some of the other final bosses!) and take on the transformed boss' attack patterns, all while still firing off its own bullet rings. Once it TurnsRed, it will shift through bosses much faster, and each form attacks far more quickly.
* BattleThemeMusic: The eponymous track, "''[[https://www.youtube.com/watch?v=8mp3gNFN61Y Delirium]]''", which perfectly matches the increasingly fast pace of the battle, at one point sounding like it's skipping like a scratched CD.
* BerserkButton: Attempting to use the [[OneHitKill Chaos Card]] on it will not only [[NoSell fail]], but also make it temporarily [[TurnsRed turn red]] and attack much faster.
* BonusBoss: In ''Four Souls'', Delirium is the only boss who doesn't grant a soul upon defeat, instead allowing the victor to gain two teasure cards. He is also one of the harder bosses despite being considered a "normal" one, having stats on par with with a Mega Boss (Satan, The Lamb, etc.) and giving other monsters a higher dice roll.
* BulletHell: Despite them being more simple, Delirium's bullet patterns manage to be worse than Hush's because it shifts into random bosses you've encountred in the run to change the pattern around, plus [[TeleportSpam it never sits still]]. This is on top of Delirium's own unique bullet patterns being fired from the bosses along with their modified patterns. By the time you've got it down to 1/4 health, it'll be firing off a new pattern before the last one even finishes.
* ContractualBossImmunity: The single enemy who isn't harmed at all by the [[OneHitKill Chaos Card]]. In fact, all it does is piss Delirium off. Plan C (kill everything then yourself three seconds later) ''does'' technically kill Delirium, but its death animation is so long that Isaac will die before Delirium does. Lazarus is the only one who can get around this thanks to his ability to resurrect in the current room (Lazarus' Rags on another character will work, but Lazarus still gets the credit).
* DamageSpongeBoss: Clocks in at a whopping '''10,000 HP''', though it mercifully doesn't have the same damage scaling that Hush and Ultra Greed do.[[note]]Well, technically, it ''does'', but the scaling resets every time it transforms, so its {{damage reduction}} is hardly even noticeable.[[/note]] Even so, it teleports all over the place, so expect to spend a ''long'' time trying to kill this thing.
* DefeatMeansFriendship: [[MindScrew It's not clear whether or not they're the same entity]], but upon defeating Delirium for the first time, the player unlocks Delirious (spawns friendly bosses on their Delirium form to fight for Isaac) and Lil' Delirium (shapeshifts into one of a handful of different familiars and wins its effects).
* DyingDream: This creature, its environment, and the ending you get for defeating it drive home the point that most of what is seen during the game was Isaac's dying hallucinations.
* EldritchAbomination: A physical manifestation of a complete mental breakdown? Yeah, it qualifies.
* EyesDoNotBelongThere: When transformed into The Husk or Conquest, Delirium will have a single eye or a pair of eyes respectively inside its mouth. Its Teratoma form also has an eye inside.
* FinalExamBoss: It's only able to transform into bosses you've previously encountered during your run; thus, learning how each boss attacks is vital for surviving the fight with Delirium.
* FlunkyBoss: Can spawn minions depending on what form it is in. Bizarrely, when it becomes the Haunt, it will often transform into a single Lil' Haunt instead, the only instance of Delirium assuming the form of a regular enemy rather than a boss. A bug also causes its health bar to disappear when this happens, but he can still be damaged in this form.
* GetBackHereBoss: With a 2x2 arena to fight in, you'll spend a fair portion of the fight trying to figure out where it teleported to. This isn't helped by it transforming into wall-hugging bosses like Mama Gurdy or extremely small ones like Isaac.
* GlowingEyelightsOfUndeath: Has yellow pinprick eyes.
* InterfaceScrew: Will occasionally cause the arena to glitch and shift from one tileset to another, causing static to briefly fill the screen in the transition. This can happen ''anywhere'' in the Void, but is far more likely to happen when fighting Delirium. It is a guarantee when Delirium is dying, but by that point, there is little in the room that can harm you.
* MarathonBoss: With its high health, constant teleporting, and shifting into whatever boss it feels like, you'll spend a large amount of time chipping this thing down to nothing.
* MeaningfulName: "Delirium" is a disturbed state of mind. The battle plays out in a deranged and bizarre way, almost like some sort of hallucination.
* MindScrew: It's a giant, melting skull that turns into the other bosses wildly and at random (many of which are considerably smaller than it), and it's encountered in an area made of all of the past floors and fails to keep a consistent theme. Considering the name, nature, and location of this boss, it's implied that the fight is Isaac's mind breaking down.
* MorphicResonance: Delirium retains its coloring and often its facial features regardless of what form it takes, allowing you to tell it apart if it happens to spawn another boss monster.
* MyLifeFlashedBeforeMyEyes: Delirium is a physical representation of the phenomenon, illustrated by its ability to shapeshift into bosses that you've encountered this run and its death animation, which plays back several moments from the current run.
* NightmareFace: A ''melting skull'' certainly isn't pleasant by any stretch of the imagination. And since its features are retained when it transforms, this can result in similar faces appearing on ''any boss in the game''.
* OminousVisualGlitch: Its level may cloak the screen with static, changing the setting of the room where that happened. After beating Delirium itself, the screen will flash with static and various images from earlier in the run for an extended period of time. In this case, the "ominous" is because it represents Isaac's mind breaking down.
* {{Shapeshifter}}: It can shapeshift into any other boss, taking on their attack patterns.
* ShapeShifterSwanSong:
** The less health it has, the more often it changes forms. At critical health, it can't stand still nor stay in a form for more than a few seconds!
** Interestingly, the ''arena'' suffers this too. During Delirium's death animation, the arena glitches and shifts between several different appearances, finally stopping as he dies. Just after beating Delirium[[note]]it changes if one leaves and re-enters the boss room[[/note]], the end result is always the Chest, as that is closest to the "reality" of where Isaac is at that moment.
* TeleportSpam: Can teleport around in any of its forms. As it loses health, this becomes more frequent, to the point that Delirium barely spends more than five seconds without doing it.
* TheThingThatWouldNotLeave: In ''The Binding Of Isaac: Four Souls'', most of the final bosses from the main game are worth 2 souls, but [[BonusBoss Delirium is worth none]]; instead, it has the gimmick that when it dies, it goes back into the monster deck, four cards down from the top. This means that once Delirium shows up, it will constantly keep returning, no matter how many times it dies, unless extremely specific measures are taken to bury it deep in the deck again.
* TimedMission: Played with. If you want to guarantee access to the Void and thus to Delirium, you have to beat Hush, which means you need to beat It Lives before the 30 minute mark (or have Mama Mega! on that floor). That said, the portal to the Void has a chance to spawn after beating Mom or any subsequent boss, increasing as you go further. Mega Satan has a 50% chance at best. He's also the only boss for whom completion is tracked even on victory laps, however, so one valid strategy is to take your time gathering items on the first run, defeat The Lamb, and then [[CurbStompBattle speedrun through the victory lap with your items]] to reach Hush.
* TrueFinalBoss: Of ''Afterbirth†''. Defeating it earns you the final ending to the game. Oddly enough, however, you can encounter it way before Mega Satan thanks to how its requirements and the level progression are set up.
** In ''Repentance'', it supposedly([[MindScrew ?]]) loses this role to Dogma and The Beast. Though if a player is skilled enough, it may be possible to defeat both of those bosses before Delirium.
* TurnsRed: The lower its health, the faster it shifts between forms and teleports.
* WeaponizedTeleportation: Even more than the ??? boss; Delirium ''loves'' [[TeleFrag to teleport directly onto you]].
[[/folder]]
[[folder:"Mother"]]
----
!!Mother
[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/400px_boss_the_witness.png]]
-> Debut: ''Repentance''
-> Floor(s): The Corpse
The [[spoiler: Disc One]] Final Boss of Repentance. Formerly known as the Witness in the ''Antibirth'' mod, she's a huge, grotesque form of Mom.
----
* AttackOfTheFiftyFootWhatever: Not as huge as she was when she was the Witness, but still quite big.
* BackFromTheDead: It's the rotting corpse of Mom, grey from time.
* BodyHorror: ''Oh yes''. Not only is she a decayed version of Mom, but when her head detaches, it exposes two more skulls where its shoulders would be.
* BulletHell: As expected of a ''Binding of Isaac'' endboss, but Mother takes this to a whole new level that would only be rivaled by Hush.
* DiscOneFinalBoss: Of ''Repentance''. She must be defeated in order to unlock the TrueFinalBoss.
* EvilOverlooker: Its boss portrait has Mother looming over Isaac in this fashion, instead of the "facing Isaac from the side" view of every single other boss.
* HellIsThatNoise: She greets you by shouting Isaac's name, much like Mom did, but with an ''extremely'' distorted voice.
* KnifeNut: One of its attacks has it pulling out and throwing a gigantic knife.
* MarathonBoss: She has a ''lot'' of health, and it isn't helped by the fact that, like Mega Satan, she doesn't have a health bar. ''Un''like Mega Satan, there's no way to tell how close you are to defeating her.
* TurnsRed: After you deal enough damage to her, her arms explode, and her head bursts out out of her body to keep attacking.
* TwoFaced: Half of her face has rotted down to the skull.
[[/folder]]
[[folder:Dogma]]
----
* AngelicAbomination: Its secondary form, which resembles an ophanim.
* FetusTerrible: It's first form is a fetus monster made of static and having an umbilical cord connected to a TV.
* OminousVisualGlitch: It's made entirely of white noise, and its first form glitches out any time it faces a new direction.
* OneWingedAngel: After the TV's destroyed, Dogma morphs from a fetus into an angelic monster.
* SnowyScreenOfDeath: A more literal example than most, as it appears to be made of TV static and is trying to murder Isaac.
[[/folder]]
[[folder:The Beast]]
* BeastOfTheApocalypse: It's in the name, and it controls the classic Four Horsemen of the Apocalypse.
* ThePawnsGoFirst: Isaac must defeat its minions, the Harbingers (sans Headless Horseman and Conquest), before he can take on the Beast itself.
* TrueFinalBoss: Of Repentance.
* UnexpectedShmupLevel: Isaac sprouts wings and takes flight to do battle with the Beast and his Horsemen.
[[/folder]]
Yes, boss''[[SerialEscalation es]]''. Your very first playthrough will end at Depths II with you killing Mom, but as you beat the game repeatedly, you unlock more chapters, each with a FinalBoss bigger and tougher than before.
All spoilers are unmarked from here on out. Proceed at your own caution!
[[folder:Mom]]
!!Mom
[[quoteright:141:https://static.tvtropes.org/pmwiki/pub/images/momleg.png]]
->Debut: ''The Binding of Isaac''
->Floor(s): The Depths, Necroplis, Dank Depths
At the end of the Depths, Isaac finally confronts his mother. As her foot stomps down on Isaac from above, she looks and sends her hands through the doors of the boss room while spawning enemies. But even if Isaac defeats Mom, it's not the end.
----
* AttackOfTheFiftyFootWhatever: Her boss fight.
* AxCrazy: Her goal is to kill her own son, and she doesn't sound too upset about it during the fight, what with the laughing and all.
* BattleThemeMusic:
** The original game had "''[[https://www.youtube.com/watch?v=_q9ZC-UwViM Thine Wrath...]]''", an orchestrated theme that sounds nearly angelic at points while still being dreadful, to symbolize Mom's willingness to kill her own son to appease what she perceives as "God".
** ''Rebirth'' gave her "''[[https://www.youtube.com/watch?v=EBJEHIxHuKE Matricide]]''", which leans more to heavy rock and an oppressive tone backed up by a choir.
* BodyHorror: The way Mom's body parts move throughout the fight (such as both eyes appearing on opposite sides of the room while she tries to stomp on you) suggest an ability to contort herself in rather...impossible ways.
* BossBanter: ''ISAAAAAC!''
* DeathByIrony: Crushed by her own bible!
* DiscOneFinalBoss: Demoted to this on your second playthrough and beyond.
* EvilIsVisceral: Likely the reason her body parts are detailed and somewhat deformed.
* EvilLaugh: She lets out one every time she successfully damages Isaac.
* EvilMatriarch: A monstrous final boss in the form of Isaac's mother.
* TheFaceless: Her entire face is never shown at any point in the main game (the intro and epilogue don't count, as they're Isaac's cartoon drawings). This is [[SubvertedTrope subverted]] after you beat the Chest in ''WOTL'' or ''Rebirth'', but only briefly. In photographs, to be precise.
* FanDisservice: When Isaac uses the Mom's Bra item, a picture of his mother's shirtless torso flashes on the screen. A ''very'' unflattering picture of his mother's less-than-fit shirtless torso.
* FatBastard: As shown by her giant leg and the picture that shows up when using Mom's Bra.
* FinalBoss: In your first playthrough. She's nowhere near the TrueFinalBoss, though.
* FlunkyBoss: She'll summon groups of random enemies to battle Isaac.
* GameplayAndStoryIntegration: Using the Bible instantly defeats her in her boss fight.
* GiantFootOfStomping: Her main method of direct attack.
* {{Gonk}}: See that leg up above? That's all the proof you need.
* GrossUpCloseUp: One of her leg in the boss portrait, and one of her body in the picture that appears when using Mom's Bra.
* HumanoidAbomination: Most of what she does in-game and in a few cutscenes blatantly disregards normal body movements if not physics. She can step on her own eye, generally alter her size, and her arm can fit in a chest inside her heart inside her womb.
* MookMaker: Spawns an array of previous enemies to make her battle harder. She does it from her body fat, which almost pours out of the boss room doors.
* MotherOfAThousandYoung: If you go by the theory that the majority of the enemies are her former children.
* SayMyName: ISAAC!
* SkippableBoss: Provided you have the Bible on you by the time you reach her, and it's fully charged.
* TacticalSuicideBoss: It's not actually mandatory, but making her stomp herself is possible and deals lots of damage.
* VoiceOfTheLegion: Her dialogue consists of her screaming "Isaac" in a demonic voice.
* WombLevel: After defeating her, you will unlock her womb as a playable level.
* YourSizeMayVary: Just how big is she? In the cutscenes, she's a normal-sized human being, but her underwear is the right size to be worn by a child visibly smaller than her, in the boss fight her leg is the length of the screen, and then her womb is big enough to have two entire levels in it, with her heart being larger than Isaac.
[[/folder]]
[[folder:Mom's Heart/It Lives!]]
!!Mom's Heart/It Lives!
[[quoteright:147:https://static.tvtropes.org/pmwiki/pub/images/momsheart.png]]
[[quoteright:103:https://static.tvtropes.org/pmwiki/pub/images/itlives.png]]
->Debut: ''The Binding of Isaac''
->Floor(s): The Womb, Utero, Scarred Womb
Defeating Mom once unlocks the Womb in subsequent playthroughs. At the end of the Womb lies Mom's Heart, which, summons enemies like Mom does. Defeating Mom's Heart reveals a Chest with something special inside. But once it's beaten enough times, it will become "It Lives!", which is Isaac as a fetus for some odd reason.
----
* BattleThemeMusic:
** "''[[https://www.youtube.com/watch?v=Zj9Ck3mNP4o ...Be Done]]''" in the original, completing Mom's theme and serving as a fast-paced theme to match the intensity of the fight.
** "''[[https://www.youtube.com/watch?v=eCW3hHhN8V4 Ventricide]]''" in ''Rebirth'', echoing Mom's theme in leaning more towards darker guitar and pounding drums with a background choir, sounding far more sinister. The term "ventricide" in itself isn't real, but it would roughly signify "death of the womb", and could be seen as a {{Pun}} on "ventricle".
* BossBanter: Has the same voice lines as Mom, only muffled.
* BossRush: It Lives has the ability to spawn {{Degraded Boss}}es such as Monstro, Larry Jr., and Chub to fight you alongside the enemies.
* BulletHell: ''Rebirth''[='=]s version shoots red tears nearly constantly throughout the whole fight, even when retreating to the back of the room.
* TheBusCameBack: The original Mom's Heart form, to an extent, in ''Afterbirth†''. While unlocking It Lives used to make it so that you can no longer fight Mom's Heart, ''Afterbirth†'' lets you fight Mom's Heart again in the Void, likely so that the Bestiary is completable for those who already unlocked It Lives. It also shows up as a possible boss encounter in the Womb stage of Greed mode.
* DamageSpongeBoss: Its lack of mobility is made up for by a big health bar. Its Eternal version in the ''Eternal Edition'' has ''even more''.
* FetusTerrible: It Lives is not just any embryo, it has been confirmed by WordOfGod to be Isaac's embryo.
* FlunkyBoss: Will summon enemies intermittently. It Lives ups the ante by spawning {{Degraded Boss}}es.
* GetBackHereBoss: Despite not moving, it accomplishes this by occasionally retreating above the screen and leaving you to deal with its flunkies for a while.
* MookMaker: Hides at the back of the room while it spawns normal enemies to fight you, then jumps back to the centre to spawn more.
* NotQuiteDead: It seems that Mom survived their fight, or at least her heart did.
* SkippableBoss: Using the Bible instantly kills it like it did with Mom.
* StationaryBoss:
** In the main game, all it can do movement-wise is pull itself upwards to hide from attacks, making bombs very useful against it.
** The Eternal form in the ''Eternal Edition'' averts this greatly; it will pursue you relentlessly around the room until it dies, still spawning enemies.
* TacticalSuicideBoss: In ''Rebirth'', it moves to the top of the screen instead of disappearing entirely. Anything that wanders up there, enemies included, takes damage.
* TrueFinalBoss: Was initially this to Mom's FinalBoss. However, this is subverted by the Halloween update, and further subverted by ''Wrath of the Lamb'' and ''Rebirth'', to the point that it's no longer anywhere ''near'' the real final boss.
[[/folder]]
[[folder:Satan]]
!!Satan
[[quoteright:144:https://static.tvtropes.org/pmwiki/pub/images/satan.png]]
->Debut: ''The Binding of Isaac''
->Floor(s): Sheol
The original TrueFinalBoss (although this isn't true as of ''Wrath of the Lamb'' and ''Rebirth''), Satan himself is the boss of what was originally the game's secret floor. Despite offering [[DealWithTheDevil Deals with the Devil]] throughout the game, he turns on Isaac and tries to kill him. His boss fight is comprised of three phases, detailed below under SequentialBoss.
----
* AttackOfTheFiftyFootWhatever: His final form is him flying far above the screen and stomping on Isaac with giant feet a la the Mom boss fight.
* BattleThemeMusic:
** "''[[https://www.youtube.com/watch?v=PhMj9tMtRs8 Enmity of the Dark Lord]]''" in ''Wrath of the Lamb'', an epic-sounding theme with techno and bells, along with heavy emphasis on bass.
** "''[[https://www.youtube.com/watch?v=Yq01zDqEOec Hericide]]''" in ''Rebirth'', a theme with heavier guitar and OminousLatinChanting, along with a deep voice growling demonically. "Hericide" roughly means "death of the master/teacher/lord".
* BlackSpeech: During the fight with him, he sounds somewhat like this. They are actually Mom's quotes, played backwards and in a much lower tone.
* DealWithTheDevil: He offers them throughout the game before you reach Sheol. Possibly even as you reach Sheol or after, if you have a Joker card on hand.
* EnergyWeapon: His second phase can fire dual Brimstone lasers from his hands (that can curve), or a single one from [[BreathWeapon his mouth]].
* EvilLaugh: Since he uses Mom's voice clips, he can do this.
* FaustianRebellion: Even if you do a ton of deals with him, you can still kill him (and the power ups from said deals can make it all the easier).
* FlunkyBoss: His first form is spawning the Fallen to fight you instead. His third phase continuously spawns Kamikaze Leeches.
* GiantFootOfStomping: His third phase has him attempting to crush Isaac with his giant hooves. They work like Mom's, but he does it much faster.
* LivingStatue: His second form is a unique boss where the statue of Satan comes to life, grows much larger, and attacks Isaac with tears and lasers.
* TheManBehindTheMan: Implied; after all, he did at the very least string Isaac along through the [[DealWithTheDevil Deals]] he makes in the devil rooms earlier on, before turning on Isaac at the last minute.
* {{Nerf}}: Satan's legs in his third phase no longer deal contact damage in ''Rebirth''.
* OneWingedAngel: After defeating his first form, he grows to massive size and attempts to stomp on you.
* PressXToDie: Using the Bible on him, which killed Mom and Mom's Heart instantly, kills ''you'' instantly instead.
* {{Satan}}: It's in his name, and he looks the part as well.
* SayMyName: Satan's battle cry when you defeat his first phase is Mom's BossBanter, only lower pitched and in reverse.
* SequentialBoss: Three phases: first a fight with The Fallen, then a fight with Satan himself on the ground with you, and finally a fight against his giant stomping legs.
* TacticalSuicideBoss: Those leeches he spawns don't just hurt Isaac.
* ThemeMusicPowerUp: When you fight the Fallen, his first phase, the regular boss theme plays. When Satan actually starts fighting, however, Hericide kicks in.
* TrueFinalBoss: He was the final boss of the game in the Halloween update, but this was trumped by ''Wrath of the Lamb'' and has just gotten further and further from the truth as more content has been added.
[[/folder]]
[[folder:Isaac]]
!!Isaac
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/isaacboss.png]]
->Debut: ''Wrath of the Lamb''
->Floor(s): Cathedral
After beating It Lives, the Cathedral is unlocked. At the end of the Cathedral resides Isaac himself.
----
* AscendToAHigherPlaneOfExistence: Appears to do this upon his defeat.
* BaldOfEvil: Justified, being a young child and all.
* BattleThemeMusic:
** The original game had "''[[https://www.youtube.com/watch?v=H4noeZx9W6s My Innermost Apocalypse]]''", a techno-rock theme that involves a [[BossRemix sad reprise of the title screen music]].
** ''Rebirth'' gave him "''[[https://www.youtube.com/watch?v=Fr2BzEgwBwM Infanticide]]''", which is entirely centered around an OminousLatinChanting and heavy guitar, with the version in-game adding a OneWomanWail.
* BeamSpam: One of his attacks in ''Rebirth'' has him covering most of the room with beams of light, except for a couple safe spots in the corners. His third phase in old versions of ''Wrath of the Lamb'' had no attacks other than rapidly dropping the beams on random spots in the room.
* BoltOfDivineRetribution: Like Conquest, he can summon several pillars of light. The safe spot is in either corner of the room perpendicular to the direction the pillars are spawning.
* BulletHell: Fires bullets in all directions, and fires at you if you hit him. Having a high-fire rate can backfire horribly.
* ChildrenForcedToKill: A subtle example. While it's easy to miss, Isaac doesn't attack at all until he takes damage.
* CounterAttack: In addition to the projectiles he fires periodically, he also fires at you whenever you damage him. In ''Rebirth'', he constantly fires in your general direction when not using another attack, instead of only doing so when hit.
* DamageSpongeBoss: Later updates in ''Wrath of the Lamb'' made him this. ''Rebirth'' instead adds more BulletHell, and makes him mobile in his third form.
* EnemyWithout: Maybe.
* [[EvilCounterpart Evil Counterpart/Good Counterpart]]:
** He seems to be the latter to Satan. He appears in a Cathedral instead of Sheol, summons angels instead of demons, and has an angelic appearance.
** He could qualify as either to the PlayerCharacter. The fight against him is most likely more symbolic than literal anyway.
* FlunkyBoss: Spawns Angelic Babies, which is fitting.
* GoOutWithASmile: Well, he is smiling in his third phase.
* HolyHandGrenade: He can cover the screen in rays of deadly light.
* MessianicArchetype: His OneWingedAngel.
* MirrorMatch: He ''is'' Isaac. Note that he's not a MirrorBoss, as he can do things you'll never be able to pull off.
* PowerGivesYouWings: In his final form. An item called Fate can be unlocked, allowing the player to have those same wings.
* PurposefullyOverpowered: You know how almost all the items added to ''Wrath of the Lamb'' are much more powerful than the ones in the base game? ''There's a reason for that.''
* SequentialBoss: Three phases: one lying in the fetal position, one standing up, and one with wings and teleportation.
* StationaryBoss: For the original game and the first two phases in ''Rebirth''.
* TroubledFetalPosition: The first part of the fight.
[[/folder]]
[[folder:???]]
!!???
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/bluebabyboss.png]]
->Debut: ''Wrath of the Lamb''
->Floor(s): The Chest
Completing the Cathedral with the Polaroid item allows Isaac to enter The Chest. At the end of this super-secret stage lies...the Blue Baby?
----
* BackFromTheDead: Is a post-mortem version of Isaac, naturally.
* BattleThemeMusic: While the original version of the fight in ''Wrath of the Lamb'' shared "''My Innermost Apocalypse''" with Isaac, ''Rebirth'' gave him a proper, original theme called "''[[https://www.youtube.com/watch?v=FT3sXT9x9CU Ascension]]''", which has discernible Latin lyrics and an aggressive rock beat with odd, creepy noises in the background at certain points.
* TheCameo: From Creator/EdmundMcMillen's flash series ''Dead Babies''.
* DivergentCharacterEvolution: In ''Wrath of the Lamb'', ??? was mostly an Isaac clone right down to having the same boss theme, with the only real differences being his ability to spawn flies and periodically shoot homing tears. ''Rebirth'' reworked both bosses, and ??? was thus given a more distinctive pattern, most noticeably removing the beams of light in favor of increasing the rate at which he spawns flies, and a unique boss theme. The distinction is most obvious in their reworked final phases: Isaac prefers to [[GetBackHereBoss fly away from the player]] at high speed while periodically teleporting away to saturate the room with beams of light, while ??? slowly flies towards the player while spawning flies and Pooters and occasionally teleporting into the player's face.
* FlunkyBoss: One way he varies from the previous boss is that he summons flies in addition to his other attacks.
* InvincibleMinorMinion: In ''Rebirth'', he gets a halo of flies, which block your tears.
* OrbitingParticleShield: ''Rebirth'' gives him two Eternal Flies to block tears partway through the fight. He also gains the ability to summon Pooters, which orbit him at high speed and can thus serve as shields in addition to attacking the player.
* PaletteSwap: He is very similar to the previous boss, Isaac, so most of the tropes above apply to him too. This resemblance is downplayed in ''Rebirth'' by giving him different attack patterns from Isaac.
* TeleportSpam: Utilized in his third phase in ''Rebirth'', with a tendency to reappear [[TeleFrag right on top of the player]].
* TrueFinalBoss: Of ''Wrath of the Lamb'', being the boss of the only sixth chapter in the game, and since beating him unlocked the game's real ending. Subverted in ''Rebirth''.
* WeaponizedTeleportation: Tries to teleport into the player during his third phase in ''Rebirth''.
[[/folder]]
[[folder:The Lamb]]
!!The Lamb
[[quoteright:169:https://static.tvtropes.org/pmwiki/pub/images/lamb.png]]
->Debut: ''Rebirth''
->Floor(s): Dark Room
Defeating Satan and completing Sheol with the Negative item allows Isaac to enter The Dark Room, a dark reflection of The Chest. The skeletal demon known as the Lamb is the boss of this stage, and it fights with powerful attacks.
----
* AllYourPowersCombined: The Lamb's volleys of shots mirror those of previous bosses. This, combined with how it switches the type of bullet with each volley, and that all of its bullets are the same colour, make it a very difficult opponent to predict.
* TheAntiChrist: In the Bible, the Lamb was a symbolic reference to Jesus. In this game, however, the Lamb is an undead demonic creature fought after Satan. The implication is that this Lamb is an alternate, [[SatanicArchetype demonic interpretation]] of Jesus.
* BattleThemeMusic: "''[[https://www.youtube.com/watch?v=DWo3PQjxogQ&t=107s The Fallen Angel]]''", a dark, creepy, fast-paced song with an ominous choir and wail.
* BlackoutBasement: When the body on his second phase is defeated, the room will darken for a brief time.
* CreepyCoolCrosses: Specifically, an upside-down one on his forehead.
* DemBones: The Lamb is essentially a demonic skeletal child with curved horns.
* DetachmentCombat: His second form involves his head floating around the room attacking you while his body lies limply on the ground spawning flies and sometimes tossing out Monstro-style shots.
* DualBoss: His second form, in which his head floats around the arena and his body stays on the ground to summon Flies and fire off a burst of tears.
* EnergyWeapon: His second form gains the ability to shoot four-way Brimstone in the cardinal directions. He can also start rotating the beams like Mom's Heart/It Lives.
* FlashStep: One of his attacks qualifies as this.
* HornedHumanoid SkullForAHead: He looks like an undead demon.
* LosingYourHead: During the second phase of the battle.
* MythologyGag: His name is a reference to the expansion for the original Isaac, named ''Wrath of the Lamb''. He is also visually similar to ''Wrath of the Lamb's'' horned skull logo. Given that Edmund had more planned for the original ''Isaac'', it's possible he was always intended to be the last boss of the expansion, but Flash's limitations meant he couldn't add him in.
* NightmareFace: Its skeletal face isn't pleasing to look at, especially in the vs. screen.
* OffModel: The Lamb's portrait in the versus screen is dark in color, but in-game and in the ''Afterbirth†'' trailer, The Lamb is coloured white.
* SequentialBoss: Has two forms, first as one entity then split into a DualBoss with its head and body.
* ShadowArchetype: In addition to mirroring other bosses, The Lamb's attacks also resemble combinations that can be used by Isaac -- for example, Monstro's Lung plus Homing Tears. Its DetachmentCombat is a lot like the Pinking Shears. It even begins the battle in Isaac's crying position!
[[/folder]]
[[folder:Mega Satan]]
!!Mega Satan
[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/theres_two_of_them.png]]
->Debut: ''Rebirth''
->Floor(s): The Chest, Dark Room
In ''Rebirth'', a giant golden door appears in the Chest and Dark Room stages. This door can be unlocked with a special item, which leads to ''Rebirth''[='=]s ultimate boss battle.
----
* AttackOfTheFiftyFootWhatever: Although the name probably gave it away.
* BattleThemeMusic: Shares "''Hericide''" with his own original form.
* BossRush: He summons bosses as he takes damage, and more if you don't do enough damage fast enough.
* BraggingRightsReward: Besides unlocking the final and definitive ending, there is no reason to fight him other than to boast you did it. The only thing you get out of winning is a new picture for your save file. There are no associated items or character unlocks, not even a mark on the character file to indicate that character beat him. This has since been [[AvertedTrope averted]] with ''Afterbirth'', as he now has his own completion mark with unlocks tied to it, in addition to counting towards the co-op baby (or Godhead, in The Lost's case) unlocked by getting all completion marks for a character on hard mode, '''and''' beating him once with every character unlocks the Mega Blast item. ''Afterbirth†'' adds another with Booster Pack 5, where defeating him once now unlocks Apollyon.
* BulletHell: What some of his attacks delve into. In his second phase, it's his ''only'' form of attack, albeit in several varieties.
* CognizantLimbs: His hands.
* DamageSpongeBoss: He's just shy of Hush in terms of overall health, and his individual forms have as much or more health than any other boss save Ultra Greed. He could actually be considered to have more health than any boss if you include the health of the mandatory boss fights. However, Mega Satan doesn't have the same damage-scaling property of those two, so he's functionally a whole lot weaker than they are.
* DemBones: Transitions from flesh and bone to just bone once he's in his second phase.
* FinalBossPreview: Regular Satan's third phase can be considered this. In Sheol, you only fight his lower half. In the Chest/Dark Room's secret room, you face the much more difficult upper half.
* FlunkyBoss: Summons The Harbingers, the Super Sins, and fallen versions of the Angels. If you take too long on one of his phases, he starts summoning regular Sins... [[TheLastOfTheseIsNotLikeTheOthers and The Hollow]].
* GiantHandsOfDoom: Accompanied by a giant head. The hands serve mainly to [[ShieldedCoreBoss block shots aimed at the head]], which is treated as the main boss. Destroying the hands will cause a set amount of damage to be dealt to the main head, and the hands [[DidntNeedThoseAnyway disappear once the second phase begins]].
* GuideDangIt: The only in-game hint you have to his existence is "The Angels await!" You're supposed to bomb the Angel statues in the Angel Rooms, prompting them to engage you; both will drop a piece of a Golden Key on defeat, and getting both pieces opens a Golden Door in the Chest/Dark Room that leads to Mega Satan.[[note]]The Golden Door also only appears once you have completed the key for the first time, which is a GuideDangIt in and of itself.[[/note]] Fortunately, completing the key also unlocks "Dad's Key" as a regular item, which can also be used on the Golden Door for future playthroughs [[note]]The "Get Out of Jail Free" card also works[[/note]].
* InterfaceScrew: The only boss [[note]]Besides the Mask Of Infamy in the original[[/note]] who doesn't have a health bar, in either form. Averted if you have the Spider Mod item, which gives him a Spider Mod health bar.
* MarathonBoss: He has two forms, each of which has as much if not more health than every other boss excluding Hush and Ultra Greed. This is on top of all the other bosses he summons. Winning takes several minutes at least, and that's if you have a good enough run.
* RedEyesTakeWarning: Considering he was the TrueFinalBoss of the game before the title was being uplifted by Delirium, you ''will'' want to take warning.
* SealedEvilInACan: Heavily implied to be sealed by the beings in the Angel Rooms.
* SequentialBoss: Including his summons, he has ''twelve'' phases.
* ShowsDamage: While not present in the first phase, cracks will start to form across Mega Satan's skull; starting with a few cracks after some damage has been done and several more appearing once some serious damage has been dealt.
* SoundtrackDissonance: Due to a bug, doing too much damage to any form will cause the calm, somber "boss defeated" music to start playing. This was eventually patched.
* TrueFinalBoss: The second to last True Final Boss of the game (which is saying something, considering there have been ''seven other candidates'' before it), hidden at the final stage and having an extra unlock process required each run. Delirium took over the role in ''Afterbirth†'', but even then it is the final boss of an alternate route that also has a 50% chance of being available from Mega Satan.
* TurnsRed: Has two full health bars, and when you take down one of them, he really cranks up the BulletHell.
* WaveMotionGun: If you stand in front of him for too long, he'll charge up a gigantic blood laser for a long time, making his head nigh-impossible to shoot.
[[/folder]]
[[folder:Hush]]
!!Hush
[[quoteright:185:https://static.tvtropes.org/pmwiki/pub/images/hush.png]]
->Debut: ''Afterbirth''
->Floor(s): ???
Defeating Mom's Heart or It Lives in under thirty minutes of total play time unlocks a short, hidden area[[note]]displayed as ??? in-game but generally called the Blue Womb or Dead Womb[[/note]]. This area only has one enemy: Hush, which appears to be another PaletteSwap of the Isaac and ??? bosses. Then he enters his ''second'' form, which is soundly described below.
----
* AttackOfTheFiftyFootWhatever: According to Edmund, it's a giant ??? pushing through the floor.
* BattleThemeMusic: Its first phase shares "''Ascension''" with ??? (because according to Edmund, it ''is'' ???), before it transitions to the heavier and oppressive "''[[https://www.youtube.com/watch?v=rbflsmpA69c Morituros]]''" when Hush's true form emerges.
* BodyHorror: Hush represents Isaac suffocating inside the chest; unsurprisingly, its "face" looks like it's being asphyxiated inside a bag.
* BonusBoss: Hush is sort of the "Isaac" counterpart to Mega Satan. While beating it does grant you a new ending, it doesn't require you to end the game. Instead, you can opt to go to Sheol/Cathedral once the fight is over. This was later patched out; defeating Hush now plays the ending and ends the run, but only the first time you beat it.
** Averted as of ''Afterbirth†''; beating Hush is the only guaranteed way to reach the Void and fight [[TrueFinalBoss Delirium]], and is required to actually unlock the Void.
* BulletHell: Its attack patterns during its second form. They even resemble the dense ring-patterns found in ''danmaku'' shooters like the ''Franchise/TouhouProject'' games; fortunately, the projectiles fired by these attacks are some of the slowest in the game.
* DamageSpongeBoss: Has the second highest health of all bosses in the game. Furthermore, its defenses scale with your damage output, so no matter what items you have, it'll take a long time to wear down. Combine this with its numerous BulletHell attacks and absurd enemy spawns, and you have a brutal boss fight.
* EldritchAbomination: As an embodiment of impending death by suffocation that looks like a giant face molded from blue flesh.
* FlunkyBoss: Begins spawning hordes and hordes of minions as the battle goes on.
* MarathonBoss: Hush has 6666 health and has a damage resistance mechanic which hardcaps how much damage you can do at once. Even an overpowered build will still take ten minutes to kill this thing.
* MeaningfulName: To hush is "to put at rest", and seeing as this boss represents Isaac slowly suffocating in the Chest, the name is ''quite'' appropriate.
* NumberOfTheBeast: Its base HP is 6666.
* OcularGushers: When low on health, Hush will fire out geyser-like streams of tears from its eyes that track you like a pair of KillSat [[EnergyWeapon lasers]].
* SequentialBoss: Fights like Isaac and ??? at first, but then it teleports away and its huge face comes out of the floor, firing loads of bullets.
* StationaryBoss: Mostly. It begins laying on the ground, as a variant of Isaac and ???, then turns into a large bullet-spewing head. The head can move around, but generally, it stays still when attacking.
* SuspiciousVideoGameGenerosity: Before the fight, the game gives you two item rooms, four golden chests, and a shop. Needless to say, ''you will need them''.
* ThemeMusicPowerUp: The first phase of the fight has ''Ascension'' playing in the background. Once the second phase begins, the music changes to Hush's own theme, ''Morituros''.
* TrickBoss: Shares a boss theme with ??? and fights like him, with a health bar that goes all the way down to zero, so you'd think that's all there is to him. Nope.
* WrapAround: It fires shots that go out of the room and then come back from the other side. Notably, these shots actually get ''faster'' after the wrap-around.
* ZergRush: Easily spawns more enemies than any other boss in the game, throwing entire floors' worth of flies, Gapers, and Boils at you throughout the fight.
[[/folder]]
[[folder:Ultra Greed/Ultra Greedier]]
!!Ultra Greed/Ultra Greedier
[[quoteright:161:https://static.tvtropes.org/pmwiki/pub/images/ultra_greed.png]]
[[quoteright:160:https://static.tvtropes.org/pmwiki/pub/images/ultra_greedier.png]]
->Debut: ''Afterbirth'' (Ultra Greed)\\
''Afterbirth†'' (Ultra Greedier)
The final boss of Greed Mode fought in a stage named after him. A giant version of Greed that uses coins to attack, summon minions or heal. ''And he still makes you drop money when hit''.
----
* AnimationBump: Ultra Greed moves around a ''lot'', and the animations are ''extremely'' smooth and detailed.
* AttackOfTheFiftyFootWhatever: A massive variant of Greed.
* BanditMook: Like his smaller versions, his attacks will cause you to drop money. Unlike the others, however, he will actively pick up the money you drop, which heals him slightly.
* BossRemix: "''[[https://www.youtube.com/watch?v=mhdlLlRMH_c Chorus Mortis]]''". It incorporates elements of the shop and arcade themes, the latter of which is, itself, a remix of the title screen.
* CripplingOverspecialization: Ultra Greedier uses almost nothing but explosive attacks. With Pyromaniac or the Host Hat, he is literally incapable of harming you outside of contact damage and highly telegraphed lasers.
* DamageSpongeBoss: His health is slightly higher than that of Mega Satan's first form, making him third overall, and the damage scaling means he'll last a whole lot longer.
* DefendCommand: One of his abilities is to shield himself with his arms, reducing all damage dealt to him, which he usually uses when he has flunkies or bomb coins active.
* EnergyWeapon: In his second form, the doors shoot gold Brimstone beams whenever he pounds the ground.
* FanDisservice: [[https://bindingofisaacrebirth.gamepedia.com/File:Boss_Ultra_Greed_back.png Has a large, visible, and well-detailed butt]]. He's also a massive corpse-like monster that ultimately has a little boy as the base of his design, and might even ''be'' an alternate version of a little boy.
* FinalBoss: Of Greed Mode.
* FlunkyBoss: Can spawn Keepers close to himself, call more minions from the arena's doors, and drop a bunch of large coins that will cast buffs on him if they're not destroyed.
* TheGambler: His primary attack depends on the outcome of a slot machine. Although it's not ''that'' much of a gamble since every outcome is pretty terrible for you. You're just hoping that he gets one of the ''less'' terrible ones.
* KingMook: To Greed and all of his mook counterparts.
* MadBomber: One of his slot machine attacks is to drop giant bomb coins all over the arena. Ultra Greedier gains an explosive effect on all of his attacks.
* MarathonBoss: His health is about half that of Hush, but he shares the same damage reduction mechanic to prevent you from winning too fast. Furthermore, he has the ability to heal during the fight, though not by much. Greedier Mode is even worse, as there's the second half to his fight.
* MoneyToThrowAway: Uses large coins as projectiles. At times, huge ones fall from above. They can explode, heal Ultra Greed, or allow him to summon minions if you don't get rid of them.
* NoCureForEvil: A notable aversion. He's unique in his ability to heal through heart coins, though it isn't very much. He'll also heal a little if he picks up the coins you drop.
* NooseNecktie: Like all other versions of Greed. The main difference being that you get to see Ultra Greed snap it loose himself.
* PaletteSwap: Ultra Greedier, Ultra Greed's gold-colored form.
* SequentialBoss: In ''Afterbirth†'', he becomes this in Greedier Mode. After beating his first form, his statue (now called Ultra Greedier) will start attacking.
* SpinAttack: Does spinning lariats when you're close.
* StoneWall: His attacks, unlike most other final bosses, don't employ BulletHell and are comparatively easy to avoid. He makes up for this by being able to tank attacks that only Hush could withstand, with his damage reduction ensuring that he will always last for a few minutes. The challenge comes not from dodging him, but from ''outlasting'' him.
* TacticalSuicideBoss: Downplayed compared to most examples, but his bomb coins can damage him as well. He uses his DefendCommand to block most of the damage. His second form is even worse in this regard since all of his attacks have explosive properties and he no longer defends. Half of the time you won't land the final hit that kills him.
* TakenForGranite: Ultra Greed turns into a solid gold statue when killed. Midas' Touch (touched enemies temporarily turn into gold) applies a penalty to his damage scaling property, letting you deal greatly increased damage. In Greedier Mode, he keeps attacking as a statue and explodes into a fine gold dust on death.
* TurnsRed: As he loses health, his attacks become faster and he spawns more giant coins, which also take effect more quickly. He also visually becomes redder as an indication of this. He also does this whenever heals via the Heart Coins from his slot machine or by picking up coins; the more he heals, the redder he gets. This is only temporary, however.
* YourPrincessIsInAnotherCastle: On your first run through Greedier Mode. So you've beaten Ultra Greed, he's turned to a statue, and you wait for the Greed Machine to spawn... but it doesn't, and after a long pause, Ultra Greed's statue starts attacking you. This new form is appropriately called Ultra Greedier. He doesn't bother with the pretense on subsequent runs and will begin attacking in his statue form almost immediately.
[[/folder]]
[[folder:Delirium]]
!!Delirium
[[quoteright:192:https://static.tvtropes.org/pmwiki/pub/images/portrait_delirium.png]]
->Debut: ''Afterbirth†''
->Floor(s): The Void
The penultimate final boss of the entire game, added in ''Afterbirth†''. Beating Hush will unlock The Void, made up of various different environments from the game, with this as the boss of one of its several boss rooms. It first appears to be a giant, melting skull, but will shift forms to white variations of the previous bosses.
----
* AmbiguousGender: Being less of a "person" and more of a manifestation of a mental breakdown that can change into almost any other boss from the game that takes the form of a gigantic skull, it's difficult to tell if Delirium even has a gender in the first place. A Tweet from Edmund [=McMillen=] during the promotion of ''Four Souls'' refers to Delirium with "him", however.
* AllYourPowersCombined: This is the boss' primary attack method. It will randomly transform into almost any other boss found throughout the game (including some of the other final bosses!) and take on the transformed boss' attack patterns, all while still firing off its own bullet rings. Once it TurnsRed, it will shift through bosses much faster, and each form attacks far more quickly.
* BattleThemeMusic: The eponymous track, "''[[https://www.youtube.com/watch?v=8mp3gNFN61Y Delirium]]''", which perfectly matches the increasingly fast pace of the battle, at one point sounding like it's skipping like a scratched CD.
* BerserkButton: Attempting to use the [[OneHitKill Chaos Card]] on it will not only [[NoSell fail]], but also make it temporarily [[TurnsRed turn red]] and attack much faster.
* BonusBoss: In ''Four Souls'', Delirium is the only boss who doesn't grant a soul upon defeat, instead allowing the victor to gain two teasure cards. He is also one of the harder bosses despite being considered a "normal" one, having stats on par with with a Mega Boss (Satan, The Lamb, etc.) and giving other monsters a higher dice roll.
* BulletHell: Despite them being more simple, Delirium's bullet patterns manage to be worse than Hush's because it shifts into random bosses you've encountred in the run to change the pattern around, plus [[TeleportSpam it never sits still]]. This is on top of Delirium's own unique bullet patterns being fired from the bosses along with their modified patterns. By the time you've got it down to 1/4 health, it'll be firing off a new pattern before the last one even finishes.
* ContractualBossImmunity: The single enemy who isn't harmed at all by the [[OneHitKill Chaos Card]]. In fact, all it does is piss Delirium off. Plan C (kill everything then yourself three seconds later) ''does'' technically kill Delirium, but its death animation is so long that Isaac will die before Delirium does. Lazarus is the only one who can get around this thanks to his ability to resurrect in the current room (Lazarus' Rags on another character will work, but Lazarus still gets the credit).
* DamageSpongeBoss: Clocks in at a whopping '''10,000 HP''', though it mercifully doesn't have the same damage scaling that Hush and Ultra Greed do.[[note]]Well, technically, it ''does'', but the scaling resets every time it transforms, so its {{damage reduction}} is hardly even noticeable.[[/note]] Even so, it teleports all over the place, so expect to spend a ''long'' time trying to kill this thing.
* DefeatMeansFriendship: [[MindScrew It's not clear whether or not they're the same entity]], but upon defeating Delirium for the first time, the player unlocks Delirious (spawns friendly bosses on their Delirium form to fight for Isaac) and Lil' Delirium (shapeshifts into one of a handful of different familiars and wins its effects).
* DyingDream: This creature, its environment, and the ending you get for defeating it drive home the point that most of what is seen during the game was Isaac's dying hallucinations.
* EldritchAbomination: A physical manifestation of a complete mental breakdown? Yeah, it qualifies.
* EyesDoNotBelongThere: When transformed into The Husk or Conquest, Delirium will have a single eye or a pair of eyes respectively inside its mouth. Its Teratoma form also has an eye inside.
* FinalExamBoss: It's only able to transform into bosses you've previously encountered during your run; thus, learning how each boss attacks is vital for surviving the fight with Delirium.
* FlunkyBoss: Can spawn minions depending on what form it is in. Bizarrely, when it becomes the Haunt, it will often transform into a single Lil' Haunt instead, the only instance of Delirium assuming the form of a regular enemy rather than a boss. A bug also causes its health bar to disappear when this happens, but he can still be damaged in this form.
* GetBackHereBoss: With a 2x2 arena to fight in, you'll spend a fair portion of the fight trying to figure out where it teleported to. This isn't helped by it transforming into wall-hugging bosses like Mama Gurdy or extremely small ones like Isaac.
* GlowingEyelightsOfUndeath: Has yellow pinprick eyes.
* InterfaceScrew: Will occasionally cause the arena to glitch and shift from one tileset to another, causing static to briefly fill the screen in the transition. This can happen ''anywhere'' in the Void, but is far more likely to happen when fighting Delirium. It is a guarantee when Delirium is dying, but by that point, there is little in the room that can harm you.
* MarathonBoss: With its high health, constant teleporting, and shifting into whatever boss it feels like, you'll spend a large amount of time chipping this thing down to nothing.
* MeaningfulName: "Delirium" is a disturbed state of mind. The battle plays out in a deranged and bizarre way, almost like some sort of hallucination.
* MindScrew: It's a giant, melting skull that turns into the other bosses wildly and at random (many of which are considerably smaller than it), and it's encountered in an area made of all of the past floors and fails to keep a consistent theme. Considering the name, nature, and location of this boss, it's implied that the fight is Isaac's mind breaking down.
* MorphicResonance: Delirium retains its coloring and often its facial features regardless of what form it takes, allowing you to tell it apart if it happens to spawn another boss monster.
* MyLifeFlashedBeforeMyEyes: Delirium is a physical representation of the phenomenon, illustrated by its ability to shapeshift into bosses that you've encountered this run and its death animation, which plays back several moments from the current run.
* NightmareFace: A ''melting skull'' certainly isn't pleasant by any stretch of the imagination. And since its features are retained when it transforms, this can result in similar faces appearing on ''any boss in the game''.
* OminousVisualGlitch: Its level may cloak the screen with static, changing the setting of the room where that happened. After beating Delirium itself, the screen will flash with static and various images from earlier in the run for an extended period of time. In this case, the "ominous" is because it represents Isaac's mind breaking down.
* {{Shapeshifter}}: It can shapeshift into any other boss, taking on their attack patterns.
* ShapeShifterSwanSong:
** The less health it has, the more often it changes forms. At critical health, it can't stand still nor stay in a form for more than a few seconds!
** Interestingly, the ''arena'' suffers this too. During Delirium's death animation, the arena glitches and shifts between several different appearances, finally stopping as he dies. Just after beating Delirium[[note]]it changes if one leaves and re-enters the boss room[[/note]], the end result is always the Chest, as that is closest to the "reality" of where Isaac is at that moment.
* TeleportSpam: Can teleport around in any of its forms. As it loses health, this becomes more frequent, to the point that Delirium barely spends more than five seconds without doing it.
* TheThingThatWouldNotLeave: In ''The Binding Of Isaac: Four Souls'', most of the final bosses from the main game are worth 2 souls, but [[BonusBoss Delirium is worth none]]; instead, it has the gimmick that when it dies, it goes back into the monster deck, four cards down from the top. This means that once Delirium shows up, it will constantly keep returning, no matter how many times it dies, unless extremely specific measures are taken to bury it deep in the deck again.
* TimedMission: Played with. If you want to guarantee access to the Void and thus to Delirium, you have to beat Hush, which means you need to beat It Lives before the 30 minute mark (or have Mama Mega! on that floor). That said, the portal to the Void has a chance to spawn after beating Mom or any subsequent boss, increasing as you go further. Mega Satan has a 50% chance at best. He's also the only boss for whom completion is tracked even on victory laps, however, so one valid strategy is to take your time gathering items on the first run, defeat The Lamb, and then [[CurbStompBattle speedrun through the victory lap with your items]] to reach Hush.
* TrueFinalBoss: Of ''Afterbirth†''. Defeating it earns you the final ending to the game. Oddly enough, however, you can encounter it way before Mega Satan thanks to how its requirements and the level progression are set up.
** In ''Repentance'', it supposedly([[MindScrew ?]]) loses this role to Dogma and The Beast. Though if a player is skilled enough, it may be possible to defeat both of those bosses before Delirium.
* TurnsRed: The lower its health, the faster it shifts between forms and teleports.
* WeaponizedTeleportation: Even more than the ??? boss; Delirium ''loves'' [[TeleFrag to teleport directly onto you]].
[[/folder]]
[[folder:"Mother"]]
----
!!Mother
[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/400px_boss_the_witness.png]]
-> Debut: ''Repentance''
-> Floor(s): The Corpse
The [[spoiler: Disc One]] Final Boss of Repentance. Formerly known as the Witness in the ''Antibirth'' mod, she's a huge, grotesque form of Mom.
----
* AttackOfTheFiftyFootWhatever: Not as huge as she was when she was the Witness, but still quite big.
* BackFromTheDead: It's the rotting corpse of Mom, grey from time.
* BodyHorror: ''Oh yes''. Not only is she a decayed version of Mom, but when her head detaches, it exposes two more skulls where its shoulders would be.
* BulletHell: As expected of a ''Binding of Isaac'' endboss, but Mother takes this to a whole new level that would only be rivaled by Hush.
* DiscOneFinalBoss: Of ''Repentance''. She must be defeated in order to unlock the TrueFinalBoss.
* EvilOverlooker: Its boss portrait has Mother looming over Isaac in this fashion, instead of the "facing Isaac from the side" view of every single other boss.
* HellIsThatNoise: She greets you by shouting Isaac's name, much like Mom did, but with an ''extremely'' distorted voice.
* KnifeNut: One of its attacks has it pulling out and throwing a gigantic knife.
* MarathonBoss: She has a ''lot'' of health, and it isn't helped by the fact that, like Mega Satan, she doesn't have a health bar. ''Un''like Mega Satan, there's no way to tell how close you are to defeating her.
* TurnsRed: After you deal enough damage to her, her arms explode, and her head bursts out out of her body to keep attacking.
* TwoFaced: Half of her face has rotted down to the skull.
[[/folder]]
[[folder:Dogma]]
----
* AngelicAbomination: Its secondary form, which resembles an ophanim.
* FetusTerrible: It's first form is a fetus monster made of static and having an umbilical cord connected to a TV.
* OminousVisualGlitch: It's made entirely of white noise, and its first form glitches out any time it faces a new direction.
* OneWingedAngel: After the TV's destroyed, Dogma morphs from a fetus into an angelic monster.
* SnowyScreenOfDeath: A more literal example than most, as it appears to be made of TV static and is trying to murder Isaac.
[[/folder]]
[[folder:The Beast]]
* BeastOfTheApocalypse: It's in the name, and it controls the classic Four Horsemen of the Apocalypse.
* ThePawnsGoFirst: Isaac must defeat its minions, the Harbingers (sans Headless Horseman and Conquest), before he can take on the Beast itself.
* TrueFinalBoss: Of Repentance.
* UnexpectedShmupLevel: Isaac sprouts wings and takes flight to do battle with the Beast and his Horsemen.
[[/folder]]
