True Eye of Cthulhu

Not much is known about this creature. It is summoned by the Moon Lord, who is considered to be the 'final boss' of the game.

Attack
The True Eye of Cthulhu will appear after either hand of the Moon Lord has been slain. They will orbit the Moon Lord and pursue the player, generating white balls of energy which they then fling at the player frequently. They also have a miniature beam similar to the Moon Lord's eyebeam that generates from his head, though the beam generated by the True Eye of Cthulhu is far easier to avoid.

Trivia
The name of this enemy tells that the Eye of Cthulhu boss fought earlier in the game isn't actually Cthulhu's eye, and judging by the fact that the eye originates from the Moon Lord, it is highly likely that the Moon Lord is in fact Cthulhu, or at least directly related to Cthulhu somehow.