Biome Keys

Biome Keys are Hardmode, pre-Plantera items used to open Biome Chests. Each key has a 0.04% (1/2500) chance of dropping from a monster in the key's respective biome. Biome Keys are consumed upon use. In the 1.3.0.1 update, key molds are no longer dropped, but instead the key itself. (like before the 1.2.1 update) The Biome Keys are "cursed by a powerful Jungle creature" which refers to Plantera and until this boss is defeated the keys remain unusable to open any of their respective chests.