Corrosion Key

The Corrosion Key is a Hardmode item used to open the Corrosion Chest in the Dungeon. Though unusable until Plantera is defeated, it can be dropped at any time during Hardmode. It has a 0.04% (1/2500) chance of dropping from an enemy in The Corrosion.

Any enemy in the biome that will drop coins when killed can drop the key, not just biome-exclusive enemies. Keys cannot be dropped by Meteor Heads (which don't drop coins in Hardmode), enemies spawned by a statue, Critters, or any enemy spawned by a pillar in the Lunar Events. Additionally, enemies in Hybrid Biomes have a chance to drop any key from its composite biomes. The biome is determined by which biome the player currently is in, not the enemy killed.

Any Biome Key dropped prior to defeating Plantera will display the tooltip "It has been cursed by a powerful Jungle creature" and will be unable to open its respective chest until Plantera is defeated. However, cursed keys are usable in worlds where Plantera has already been defeated. The Corrosion Key is consumed upon use.