If Isaac dies in a Sacrifice Room, a puzzle piece will appear on his last will. Dying in Sacrifice Room while holding it unlocks The Lost. If The Lost is unlocked, revives Isaac as The Lost on death then disappears.
Quote
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Effects
- Dying in a Sacrifice Room while holding it will unlock The Lost.
- If Isaac dies while holding this trinket and has already unlocked The Lost, he will be revived in the previous room as The Lost and Missing Poster will be consumed.
- If Tainted Lost dies while holding the trinket, he does not become the normal Lost.