Keys are one of the primary items in the player's inventory, displayed below bombs on the HUD.
You can carry up to 99 keys at a time, any additional keys collected will not be counted.
Keys can be found in chests, x marks the spot rocks, slot machines, beggars, shops, the shell game, champion enemies and sometimes in extinguished fires.
Each key can only be used once before it is depleted and will unlock any one door, chest or key stone when used.
Keys in shops cost 5 coins, 3 when on sale.
Keys are required to open:
The Treasure Room
Contains a random free treasure. Always unlocked in the Basement/Cellar 1.
Contains a selection of items for sale with at least one treasure.
Contains two free Book Items, appears identical to the shop outside but is marked differenty on the mini map. Available in the Wrath of the Lamb DLC.
Contains a random selection of loot, possibly a treasure or another chest.
Blocks access to a dungeon feature, may drop a random pickup on rare occasion. Found in the Depths or the Necropolis.
Added in Wrath of the Lamb. A golden key will rarely replace a normal key when one is dropped. This key, when held, will open any and all locked doors and keystones for the current floor without reducing the number of keys carried. This effect wears off when you leave that floor. Picking up multiple golden keys on one floor will not have any effect. Owning a golden key is visible on the map, since it alters the icon for the amount of keys.
The Skeleton Key This item maxes out your keys to 99 when picked up!
Flat Penny Added in Wrath of Lamb. This Trinket gives a 50% chance of spawning a key when collecting a coin. A golden key can be occasionally spawned under the same circumstances.
Rusted Key Added in Wrath of Lamb. This trinket increases the chance of keys/Golden Keys spawning after clearing a room.