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Crystal Key

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How do you unlock Crystal Key?

In The Binding of Isaac, Crystal Key is unlocked by earning the Mother completion mark as Tainted Lost.

Structured pathSource-backed requirements are mapped into trackable steps.

Whenever Isaac clears a room, has a chance to open a neighboring Red Room.

Crystal Key (Achievement)
- Tainted Lost → Mother (normal)
  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
  - Tainted Lost

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What unlocking Crystal Key leads to

Nothing depends on this yet.

Source: bindingofisaacrebirth.wiki.gg

Imported 2026-09-13