Buddy Baby

AchievementAfterbirthUnlock unknown

Achievement details

Achievement number: 253
Description: Unlocked a new co-player baby.
Requirement: Earn all Hard mode Completion Marks as Isaac

How do you unlock Buddy Baby?

In The Binding of Isaac, Buddy Baby is unlocked by earning every hard-mode completion mark as Isaac (Character).

Structured pathSource-backed requirements are mapped into trackable steps.

Unlocked a new co-player baby.

See the full unlock path for Buddy Baby — 13 steps

All of
- Isaac (Character) → Mom's Heart or It Lives! (hard)
  - Isaac (Character)
- Isaac (Character) → Isaac (hard)
  - Isaac (Character)
- Isaac (Character) → ??? (hard)
  - Isaac (Character)
- Isaac (Character) → Satan (hard)
  - Isaac (Character)
- Isaac (Character) → The Lamb (hard)
  1. Defeat Satan 5 times to unlock The Negative. source
  2. The Negative is a guaranteed drop from Mom; take it, then defeat Satan in Sheol and touch the chest to enter Dark Room. source
  3. Find and defeat The Lamb in Dark Room. source
  - Isaac (Character)
- Isaac (Character) → Mega Satan (hard)
  1. ??? or The Lamb must be defeated once for the Golden Gate to spawn. source
  2. Open the Golden Gate by combining Key Piece 1 and Key Piece 2 into the Golden Key, or by using Dad's Key or another gate-opening effect. source
  3. Reach the starting room of Chest or Dark Room, pass through the Golden Gate, and defeat Mega Satan. source
  - Isaac (Character)
- Isaac (Character) → Boss Rush (hard)
  - Isaac (Character)
- Isaac (Character) → Hush (hard)
  1. Defeat Mom's Heart for the 10th time to unlock Blue Womb. source
  2. Defeat Mom's Heart or It Lives! within 30 minutes and enter the door to Blue Womb. source
  3. Defeat Hush in Blue Womb. source
  - Isaac (Character)
- Isaac (Character) → Ultra Greedier (hard)
  - Isaac (Character)
- Isaac (Character) → Delirium (hard)
  1. Defeat Hush to unlock The Void. source
  2. A Void portal can appear after a major boss; defeating Hush guarantees one. source
  3. Defeat Delirium, the main boss of The Void. source
  - Isaac (Character)
- Isaac (Character) → Mother (hard)
  1. Defeat Hush 3 times to unlock A Secret Exit. source
  2. After A Secret Exit is unlocked, a locked door to Downpour appears after completing Basement/Cellar/Burning Basement I or II. source
  3. Collect Knife Piece 1 in Downpour/Dross II. source
  4. Collect Knife Piece 2 in Mines/Ashpit II. source
  5. After defeating Mom in Mausoleum/Gehenna II, stab the flesh door that appears with the knife familiar to open it. source
  6. Defeat the Mausoleum version of Mom's Heart behind the flesh door, then reach Corpse II and defeat Mother. source
  - Isaac (Character)
- Isaac (Character) → The Beast (hard)
  1. A Strange Door is unlocked by beating Mother for the first time. source
  2. Take The Polaroid or The Negative after Mom, escape the boss room, then use it to open A Strange Door. source
  3. Find Dad's Note, complete the Ascent to Home, then defeat Dogma, the Ultra Harbingers, and The Beast. source
  - Isaac (Character)

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What unlocking Buddy Baby leads to

Dead God

Source: bindingofisaacrebirth.wiki.gg

Imported 2026-09-13