Keystone is a trinket in Fiend Folio, a mod for The Binding of Isaac.

On pickupSpawns a Key.

While heldGrants the following stat boosts for every key used on the floor:
+0.1 speed.
+0.09 tears.

The stat increases last only for the current floor.

The following special synergies and interactions for Keystone have been documented.

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

• Check out the trinket description on the mod's external Wiki.
• Download Fiend Folio from the Steam Workshop.