Biome Key Molds

Biome Key Molds are extremely rare Hardmode items used to craft Biome Keys for Biome Chests. When in hardmode every enemy has a 0.04% (1 in 2500) chance of dropping a Biome Key Mold. The type of Biome Key Mold that is dropped depends on the biome you are currently in (Jungle, Corruption, Crimson, Hallow or Snow).

Tips

 * Molds are an extremely rare drop, and can take hours to farm. Note that there is a limit to the number of items that can remain dropped at once, so leaving a farm running for hours unattended can result in molds being dropped and then disappearing due to the limit being reached.
 * Enemy spawn rates are higher during a Blood Moon, even underground, which makes a good time to farm for Molds. The Water Candle and Battle Potion also increase spawn rates.
 * Terraria's server software (or turning off "Autopause" on single player) can help farm for rare drops like Biome Molds by allowing the game to run in the background.