This article is about the boss at the end of The Chest. For the playable character, see Blue Baby. For the floor, see Blue Womb. For the pill effect, see Pills. For other uses, see ??? (Disambiguation).
??? is the final boss of The Chest, accessed by defeating Isaac in the Cathedral while holding 
The Polaroid. He is a posthumous version of Isaac.
Behavior
During all three of ???'s phases, he will always shoot multiple tears in the player's direction at fixed intervals. These tears can be double tears and have a small chance to be homing tears.
??? will not begin attacking the player until he takes damage.
Phase 1
- Shoots rapid-fire lines of tears that curve as they move.
- Shoots rapid-fire lines of tears in eight directions with varying intensity and speed.
Phase 2
- Two Eternal Flies begin to circle ???, occasionally blocking tears.
- Summons Attack Flies, Moters, Pooters, or Super Pooters to orbit around himself.
- Fires 4 homing tears in a lop-sided X pattern.
- Fires 8 homing tears in every direction.
Phase 3
- Spawns flies more aggressively.
- ??? will teleport at a distance in front of the player, either in the last direction he was moving or directly onto the player if he didn't move at all. ??? will not teleport if he is slowed (e.g. with a
Stop Watch). - Shoots rapid-fire lines of tears that curve as they move.
Gallery
- Boss BlueBaby1.png
First phase of ???.
Second phase of ???.
Third phase of ???.
??? as one of Delirium's forms.
Unlockable Items
- 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.
Defeat ??? or 
Defeat ??? or 
Defeat 
Defeat ??? or - 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.
- Golden God! - Defeat ??? and The Lamb.
- Celtic Cross - Defeat ??? asMagdalene.
- Cain's Eye - Defeat ??? asCain.
- Sacrificial Dagger - Defeat ??? asEve.
- Blood Penny - Defeat ??? asSamson.
- Store Credit - Defeat ??? asLazarus.
- Mysterious Paper - Defeat ??? asEden.
5 / 
9 (except In addition, beating ??? with a particular character for the first time will place a Polaroid Completion Mark on that character's post-it note.
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, are the only two bosses who do not "die" upon losing all their health. Instead, ??? teleports away and the battle ends.
- ??? is commonly referred to as the 'blue baby' by the Binding of Isaac community, as well as Steam Achievements.
- An identical ??? fight, with identical behavior and music, is used as the first phase of Hush, using a different sprite. The Hush version also has half the HP.
- ??? is one of the only bosses who's one of Delirium's forms that doesn't have any melted features, along with both of the angels.
References
 The Binding of Isaac: Rebirth
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