The Mechanical Eye is a Hardmode boss-summoning item used to summon The Twins, the Hardmode version of the Eye of Cthulhu. It can only be used at night; attempting to use this item during the day will not spawn the Twins nor consume the item. The Mechanical Eye is also unusable while the Twins are already alive. If the Twins have not been defeated yet in a Hardmode world, all enemies have a 1/2500 (0.04%) chance of dropping a Mechanical Eye, with the exception of statue-spawned enemies, Meteor Heads, and Old One's Army enemies.
- (Desktop, Console and Mobile versions) In the get fixed boi secret world seed, the Mechanical Eye is not consumable and is instead a crafting material for the Ocram's Razor, an item used to summon Mechdusa.
- Like other mechanical boss-summoning items, the Mechanical Eye can be brought to pre-Hardmode worlds and will successfully summon The Twins there.
- As with several items, the Mechanical Eye has multiple crafting recipes (two in total) due to some items in the recipe allowing substitutes.
- The Mechanical Eye is the only mechanical item with no visible winder.
- Desktop 1.2.1: Drop chance now reduced from 1 in 1000 to 1 in 2500.