Crimson Key Mold

The Crimson Key Mold is a rare drop used to craft the Crimson Key, which is in turn used to unlock the Crimson Chest in the Dungeon. The mold can be found from any monster in the Crimson biome with a 1/2500 drop rate, or a 0.04% chance after the world have entered hard mode (i.e. you must kill the wall of flesh before you can farm for the mold).

Farming

 * A good way to farm for the key mold is to farm the Brain of Cthulhu because the Creepers count as kills.