Mechanical Eye

The Mechanical Eye is used to summon The Twins, the Hardmode version of the Eye of Cthulhu. It can only be used at night. Using another Mechanical Eye while The Twins are already spawned will result in instant death. It can also be used in a world without hardmode activated. If you have not defeated The Twins before dawn, they will float up to the top of the screen and you will have to try again a different night.

If you have not defeated The Twins yet and are already in hardmode, all enemies (with the exception of statue-spawned monsters and meteor heads) have a 1 in 2500 chance of dropping this item.

Trivia

 * The Mechanical Eye is the only mechanical item with no visible winder.

History
Œil Mécanique 기계식 눈