The Key of Light is a craftable item which spawns a Hallowed Mimic when placed in any slot of any empty Chest. The world must be in Hardmode and the only item inside the Chest must be a single Key of Light. The Hallowed Mimic is spawned as soon as the Chest is closed, consuming both the Key of Light and the Chest.

What drops from the hallowed mimic?

It is said to be the most useful Mimic in the game, dropping the famous and widely used Daedalus Stormbow, which is used in fighting some hardmode bosses, most notably The Destroyer.

How do you spawn a crimson mimic?

The Crimson Mimic is a miniboss that spawns rarely in the Underground Crimson. They can also be spawned by putting a Key of Night into any empty chest. The chest will then turn into a Crimson Mimic in a hardmode world that contains the Crimson.