The Killer Eye debuted in Kid Icarus: Uprising. It sets up when used by the player, and it behaves like a turret, attacking foes in its vicinity.
In Super Smash Bros. 4
It initially appears in its inactive state, when it can be picked up by a player. When the holder throws it down, it activates, then launches pink energy in the direction it faces. It can be attacked by opposing fighters; if knocked on its back it will continue firing straight up, while if knocked on its front it will right itself by shooting. Despite being attacked, it will remain under the ownership of the original thrower. Any opponents within its range of vision will cause it to fire more frequently. If thrown into a wall or ceiling, it will stick there and begin shooting. If attacked enough, it will drop off.