Lunatic Cultist

The Lunatic Cultist is a Hardmode, post-Plantera boss summoned by killing all four Cultists that spawn at the Dungeon's entrance after Golem is defeated. Beating the Lunatic Cultist initiates the Lunar Events.

The boss only has one defined stage, but its attacks become progressively stronger as it loses health. During the fight, the boss will fly around seemingly at random, firing lightning, fireballs, shadowflames and exploding packed ice at the player. It also repeatedly summons the Phantasm Dragon, a Wyvern-like enemy, to attack the player if you attack an illusion of him. In addition, it will often project duplicates of itself, only one of which can be attacked to deplete the boss's health.

Trivia

 * Its lightning attack seems to be fired from a giant and immobile Magnet Sphere.
 * The packed ice it fires is similar to that of the Ice Queen.