Crimson Key

The Crimson Key is a 1/4000 drop from enemies found in the Crimson after a world has entered Hardmode. It is used to unlock the Crimson Chest found in the Dungeon.

usable farming method: get a pygmy staff, then go farm 1.5 platinum and buy the tiki armor, and pygmy necklace from the witch doctor, then hang from a block ~15 blocks from a platform in the large center cavern as picture below. reliable, semi-safe (you'll only occasionally get hit by the occasional herpling jump). all 6 pygmys and my position in cavern

alternatively; put 50 meteor blocks under you and farm meteor heads. same 6 pygmys but over a platform of meteor