??? (Boss)
??? is the boss of 
Chest, accessed by defeating 
Isaac in the 
Cathedral while holding 
The Polaroid, which is always dropped by 
Mom after defeating Isaac five times. He is a posthumous version of Isaac, and the final boss of Ending 14.
Behavior
??? lies on the ground in the middle of the room and does not begin attacking until he takes damage.
During all three of ???'s phases, he performs similar attacks to Isaac, but at a faster pace. He also shoots multiple projectiles in the player’s direction at fixed intervals. After taking enough damage, he begins to shoot double and triple projectiles.
- Each projectile has a chance of having a homing effect.
Phase 1
??? remains stationary on the ground and performs the following attacks:
- Shoots 7-8 rapid-fire lines of projectiles in all directions that expand outwards. After taking enough damage, these lines curve while travelling.
- Shoots 8 lines of 2 projectiles in all directions that expand outwards. Each line consists of one normal projectile and one homing projectile. After taking enough damage, these lines curve while travelling.
- After taking enough damage, ??? summons
Attack Flies, 
Moters, or 
Pooters that orbit around himself.
- Pooters have a farther orbit than the other flies.
- Attack Flies spawned from Moters chase Isaac instead of orbiting ???.
Phase 2
2 
Eternal Flies that can block tears begin to circle ???, who stands up but remains stationary and performs the following attacks:
- Continues to spawn orbiting flies.
- Fires 4 homing projectiles in a lop-sided X pattern.
- Fires 8 homing projectiles in all directions.
Phase 3
??? grows a pair of angelic wings and is no longer stationary, slowly drifting towards Isaac and performing the following attacks:
- Spawning orbiting eternal flies (with increasing frequency compared to the previous phase).
- Teleporting to a position in front of the player - predicting their movements and attempting to cut them off. ??? will teleport directly on top of the player if the player is stationary.
- Shooting 2 projectile patterns from the first phase.
Gallery
??? in-game.
??? in his second phase.
??? in his third phase.
??? as one of
Delirium's forms.
???'s boss portrait in the GFVELLLL seed as well as the G Fuel themed daily challenge.
??? as a can of G Fuel.
Trophy spawned after defeating G Fuel ??? in the daily challenge.
???'s old boss portrait prior to Repentance.
Unlockable Achievements
I RULE! - 
Defeat ??? or The Lamb, defeat Satan as 
Isaac, and unlock 
The Negative
Defeat ??? or The Lamb, and defeat Satan as Isaac
Defeat Mega Satan and unlock The Negative.
Ultra Hard - Defeat ??? or The Lamb. Possession of The Polaroid / The Negative is required, barring getting to 
Dark Room through a 
Sacrifice Room. Defeat Mega Satan and unlock The Negative.
5 / 
9 / 
Notes
- ??? cannot teleport during his third phase if he is slowed (e.g. using
Stop Watch).
Trivia
- ??? was added in the Wrath of the Lamb DLC for the original The Binding of Isaac.
- The music that plays during this boss fight is titled Ascension.[1] The term "ascend" is typically used in religion as the act of one's soul rising to Heaven.
- ???, along with Isaac, flies away upon defeat and does not "die".
- ??? is commonly referred to as the 'blue baby' by the Binding of Isaac community, as well as Steam Achievements.
- ??? is fought as the first phase of
Hush with identical behavior and music, only using a different sprite. The Hush version also has half the HP. - Delirium's ??? form is one of its only forms that don't have any melted features, along with both of the Angels.
-
Blighted Ovum, 
Big Horn, 
Triachnid, Isaac, and ??? are the only bosses whose portraits were completely changed in Repentance (beyond simply adding more detail). Of these, only Triachnid, Isaac, and ??? didn't receive new sprites.
- Isaac and ???'s portraits were changed to match their appearances on the transition screen between levels. This was also the case in the original Flash game.
-
- ??? has a unique sprite when encountered in the GFVELLLL seed as well as the limited time G Fuel themed daily challenge.
- This sprite was added in celebration of the release of "Isaac's Tears" flavored G Fuel.
- ??? Is also a reference to BlueBaby, Edmund's Newgrounds name.
References
 Isaac (Boss) Unlocks
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 ??? (Boss) Unlocks
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 The Binding of Isaac: Rebirth
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