- For information on the character, see ???.
Official artwork by Edmund McMillen
???, a.k.a. The Blue Baby, is the boss of The Chest and is the game's final boss in the Wrath of the Lamb expansion. His encounter is very similar to Isaac, except he is more powerful in that he fires more tears in retaliation.
Phase 1??? will appear lying down in the center of the room, crying on the floor. He shoots 12 high-velocity tears in a radial burst, some of them being purple and slightly homing, and will retaliate with streams of tears when hit, some of which may also be homing. He will also spawn Flies continuously.
Phase 2At 66% of his health, a light will shine on ???, and he jumps from the ground. He will then periodically shoot 4 large purple homing tears in all directions. He will still retaliate with tears when hit and will continue to spawn Flies.
Phase 3Triggered near 33% of ???'s health. ??? will grow angel wings, smile, and start floating. White beams will be randomly shot down from the sky (similar to Crack The Sky and White Pony), Angel Babies will start spawning frequently (up to a maximum of 6), and the same homing projectiles from before will be shot in six directions at the same time. At this point ??? will no longer retaliate with tears when hit, and will spawn Flies less frequently.
- Using The Bible during or after the fight will instantly kill the player (similar to Isaac and Satan) unless they have The Wafer item.
- Like in the Isaac fight, using items with a high fire rate (such as Technology 2) is dangerous in this fight, as ??? will retaliate with a large amount of tears upon each hit. This also applies to effects which apply damage rapidly, such as Mom's Knife.
- Applying slow effects such as Little Gish or Spider Bite to ??? will not affect the speed of his homing tears, but will slow all normal tears.
- Activating Mom's Bra or triggering the special effect of Mom's Contacts will prevent ??? from spawning enemies or attacking at all—including when damaged—for the duration of the effect.
- ??? cannot be damaged by the Crack The Sky light beams, or by his own. However, any Angel Babies in the fight can take a small amount of damage from the light beams.
- This boss is a reference to Ending 10, where Isaac finds ??? in the giant chest.
- ??? is technically an alternative version of Isaac (as a boss), having the same attacks only with some variants.
- ??? Is also a reference to BlueBaby, Edmund's Newgrounds name.
- The music for this fight is the same as the Isaac fight, My Innermost Apocalypse.
- In the second phase, ???'s tears are incorrectly shaped on his sprite, while in the third phase, his tears are falling down correctly.
- Whenever he is curling up while in his third form, he might turn into Isaac for a single frame.
- If you die after you beat him but have revive, entering the boss room will have both the boss and the chest present, but you can get to the chest to activate the ending.