Crystal Key is an unlockable trinket in The Binding of Isaac, added in the Repentance DLC.

Clearing a room has a 33% chance to open a neighboring Red Room.

The chance is reduced to 12.5% if already inside a Red Room.

For more info about red rooms, check the Red Key page.

This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this trinket for the previous Repentance version, check this page instead.

Defeat Mother as Tainted Lost.

Crystal Key can be found in the following item pools:

The following tags are applied to this trinket:

The following special synergies and interactions for Crystal Key have been documented.

* Note that not all possible synergies and interactions are listed here.

Below is the Internal Item Description as shown in-game.
Note that some stat changes are not displayed here. Please see the main description for the full effects.

Crystal Key

• 33% chance of opening a door to a red room on room clear
• Golden Trinket (without Mom's Box): 50% chance of opening a door to a red room on room clear
• Mom's Box: 50% chance of opening a door to a red room on room clear
• Mom's Box + Golden Trinket: 100% chance of opening a door to a red room on room clear
• Chances are reduced if the cleared room is a red room

• Check out the trinket description on the external Isaac Wiki.