Guide:Farming Biome Keys or Key Molds



Biome Keys are used to open Biome Chests in the Dungeon, which provide access to some powerful post-Plantera weapons, such as the Vampire Knives and Rainbow Gun. But, they drop at the very low rate of 0.04% (1/2500), and are only dropped when the player is in the key's corresponding biome. Thus, it is advisable to set up an efficient farm to obtain them.

In versions, Biome Key Molds drop in place of Biome Keys, which requires additional material from Plantera and Mechanical Bosses in order to be crafted into a Biome Key.

Events
Events are one of the best ways to farm Biome Keys and their Molds. An extremely large amount of Enemies spawn during events, and many of them will have a chance of dropping a Biome Key or Mold, supposing that you are in the biome in which one will drop.

Some events the player may want to consider using to farm:
 * Goblin Army: The enemies that spawn shouldn't be an issue for the player to deal with. However, if you are playing on, you need to take care of the Shadowflame Apparations that the Goblin Summoner may summon.
 * Frost Legion: There are few enemies in this event capable of attacking through walls, but be wary that Snow Ballas may nullify an arena if they aren't dealt with.
 * Pirate Invasion: it's easy to obtain the, and most pirates are limited to attacks that can't penetrate blocks.
 * Solar Eclipse.

Bosses
Some Bosses can be used for farming:
 * King Slime: It can spawn regular Blue Slimes, which can drop any biome-specific drop, which includes Keys;
 * Eater of Worlds: Its segments can drop any biome-specific drops, which includes Keys;

AFK Farm
The time it may take for Keys to drop makes AFK farms an option some players may consider. There are a few items that can kill monsters without player interaction: minions, Accessories, Armor sets, Lava, and Traps. Without player supervision, however, the character should be walled up as protection. The "waiting room" should be off-screen above the ground to avoid enemies that can pass through blocks, and protected by traps to prevent flying enemies from piling up, and increasing spawn rate. The event should also not feature flying enemies that can pass/attack through walls, such as Elf Copters.

Keep in mind that even while AFK-farming, the player is still required to gather loot, so to prevent items to despawn.

Arena tips
If you want to artificially build a biome to farm Key Molds in, there are two ways to do so:
 * Gradually stacking one or more block types of the relevant biome until the amount of blocks calls it forth. The compactness of the stacked blocks allows a relatively small area to create a biome. For further info, see Guide:Artificial biomes.
 * By using 200 blocks of Red Ice, 200 blocks of Purple Ice and 80 blocks of Lihzahrd Brick it will be possible to have 4 biomes overlap and all 4 biome keys to drop. Hallow is unfortunately exclusive with Crimson and Corruption, and will require a separate arena from those two.
 * The Clentaminator is an excellent tool for changing biomes. It's also possible to use Grass Seeds if the player doesn't mind waiting.
 * If you start with a Mud Block-based biome, be sure to farm the Jungle Biome Key first! When you transform it into the Corruption or Crimson, the top block layer will be transformed into Dirt Blocks, on which Jungle cannot be re-applied.
 * Unless you don't mind the Corruption, Crimson, or Hallow spreading, you may want to "quarantine" the area by digging a six blocks wide shaft and tunnel to separate the Key farms from the adjacent land.
 * A Water Candle will increase the number of enemies. This can also be combined with the Battle Potion.
 * Additional info on creating biomes/arenas can be found on:
 * Guide:Base defense and precautions
 * Guide:Maintaining world purity
 * The dungeon has a high spawn rate, so setting up a farm there can help speed up the farming process.
 * Actuators can help with getting in and out of your waiting room while blocking enemies from attacking you.

Corruption Key / Mold

 * The Eater of Worlds's body segments all count towards the drop rate of 1/2500. Since the Eater of Worlds consists of 50 segments there is a higher drop rate for a key mold from the Eater of Worlds. With Hardmode equipment, spam summoning the EoW is quick and reliable.
 * While farming, remember to return to the Dryad if a Blood Moon occurs, as she will sell Vile Powder, which is one of two ingredients in making Worm Food. The other being Rotten Chunks. This prevents the player from having to farm Vile Mushrooms, but they function as an alternative if waiting isn't an option.
 * Another, lesser, method is to kill worm type creatures like the World Feeder with explosives. This will kill multiple segments at once, each dropping their own loot.

Hallowed Key / Mold

 * This may not be the fastest strategy, but standing on a hill in The Hallow and using the Spectre Staff to kill any enemies that come into your field of view is somewhat effective.
 * A more AFK equivalent is to stand on the hill and use a Pygmy Staff along with some sentries to automatically kill the enemies. Turtle Armor can help do damage even if they get to the player, and Campfires and Heart Lanterns help boost regeneration.