The Binding of Isaac: Rebirth — How to Unlock Tainted Characters

Tainted characters are alternate versions of Isaac's roster with radically different mechanics — Tainted Lost sees only quality 4 items, Tainted Isaac rerolls items on hit, and Tainted Keeper uses coins as health. Unlocking any Tainted character requires completing Repentance's Ascent path at least once and reaching the Home floor. This is the single most searched onboarding topic in Repentance and the gateway to 17 additional characters.

Phase 1: Unlock the Alternate Path and Defeat Mother

First defeat Hush three times to earn the "A Secret Exit" achievement, which enables alternate floor doors. On future runs, use a key on Basement I/II to enter Downpour, two bombs on Caves II for Mines, and two hearts on Depths II for Mausoleum. Collect Knife Piece 1 in Downpour II (mirror world puzzle) and Knife Piece 2 in Mines II (minecart button puzzle). Assemble the knife at Mausoleum II to open the Corpse door and defeat Mother. See our alternate path guide for floor-by-floor details.

Phase 2: Open the Strange Door in Depths II

After defeating Mother once, a Strange Door appears in Depths II on subsequent runs. Defeat Mom, take The Polaroid or The Negative, then exit the boss room using The Fool card from the marked skull (always spawns on Depths II). Insert the photo into the Strange Door to enter a special Mausoleum floor. The boss room contains only Dad's Note — picking it up starts the Ascent, reversing through modified floors back toward Home.

Phase 3: Home, Red Key, and the Secret Closet

On your first Home visit, Mom's bedroom chest always contains the Red Key. Use the Red Key on the faint red outline in the hallway outside Mom's room to create a door to a secret closet containing the Tainted version of your current character. Touch the Tainted character to unlock them permanently. On repeat Home visits, drop a trinket in any item or boss room before grabbing Dad's Note — the trinket transforms into a Cracked Key during Ascent, which works identically to the Red Key for closet access.

Each Tainted character unlocks individually — replay Home as each character you want to unlock. Tainted unlocks do not require Hard mode. Cross-reference Tainted characters overview and Red Key vs Cracked Key guide for item-specific mechanics.