Demon Eye

The Demon Eye is a common flying enemy which spawns only at night, and most likely is one of the first enemies encountered by a new player. It moves in an arc-like pattern, ricocheting off of walls, and will be knocked back when struck by anything. It will follow a player until it is killed, the player moves too far off screen, or the player dies.

When killed a Demon Eye will commonly drop a lens. If your mana is not at full strength it'll also occasionally drop a Mana Crystal.

Related to Eye of Cthulhu (boss) and Servant of Cthulhu.