While trinkets are fairly common, there is always a chance one doesn't appear naturally.After starting the Ascent by collecting Dad's Note, the trinket left behind will have become a Cracked Key in the corresponding room. To create a Cracked Key (once unlocked), drop any trinket in a Boss Room or a Treasure Room on any floor before acquiring Dad's Note, including the floor Dad's Note is in.

Cracked Key's main purpose is to allow unlocking Tainted characters in Home without having to rely on finding the Red Key.The red rooms can be connected to the floor's Ultra Secret Room. These rooms are most commonly normal rooms, but have a chance to be various special rooms instead, including Devil Rooms, Angel Rooms, Shops, Treasure Rooms, etc.This is indicated by walls that have red door outlines on them. Acts as a single-use Red Key, allowing Isaac to create new rooms by using the key next to a wall where there would be no conditions that could prevent a (secret) room from appearing there.Cracked Key is a consumable item added in The Binding of Isaac: Repentance.

Skull key cracker