Encounter map
Where to find ???
Set encounterThis fight is reached on the Chest route. It is a set encounter, so it does not appear in the random floor boss pools.
See the Chest and ??? routeFight guide · Chest
How to fight ???
The Chest boss, ??? (Blue Baby), echoes Isaac's phases at a faster pace and adds flies and homing shots.
Before entering
Expect three phases after reaching the Chest. The boss begins attacking once damaged.
- 1
Opening volleys
Watch for: ??? fires rapid rings, some with homing projectiles, and begins summoning orbiting flies.
Try: Stay mobile, preserve distance, and watch for a curved or homing shot after the first gap passes.
- 2
Orbiting cover
Watch for: Eternal Flies circle the standing boss and can block your tears while homing volleys continue.
Try: Shift your firing angle as the flies rotate, and leave yourself a route around incoming shots.
- 3
Winged phase
Watch for: The boss drifts toward Isaac and can teleport ahead of the player's movement.
Try: Avoid remaining still and change direction when the teleport threatens your current lane.
Completion mark
??? character rewards
Defeating ??? records the ??? (Chest) mark for the character you are playing. Check the clear level beside each reward. Some require Hard mode. The reviewed list has 16 direct reward entries tied to this completion target. These are achievement unlocks, not items dropped by the boss.
Multi-mark and roster-wide achievements appear in the completion tracker.
Game-file referenceRaw data and official artEntity fields, portrait files, and source notes for this boss.
Raw entity values
Health and entity data
- Base HP
- 2000
- Stage HP scaling value
- 0
- Entity ID and variant
- 102.1
- Contact damage field
- 1
These are raw entity fields. Armor, floor scaling, phase transitions, shared health, and scripted waves can make the fight differ from the base HP value.
Asset mapping
Official portrait assets
The ??? versus-screen portrait comes from the supplied game art. The original filenames are retained below.
- Portrait file
- Portrait_102.1_BlueBaby.png
- Boss-name image file
- BossName_102.1_BlueBaby.png
Source notes
How this record is built
Boss identity and portrait metadata come from bossportraits.xml. Random floor membership, weights, and Double Trouble room IDs come from bosspools.xml. Health and entity fields come from entities2.xml. Fixed story locations and route explanations are reviewed editorial context.