Lunatic Cultist

The  is a boss that spawns after killing the four Ancient Cultists that spawn at the entrance to the Dungeon after killing the Golem, but if you have removed the top of the dungeon, it will not spawn. Defeating the Lunatic Cultist triggers the Celestial Event. After you defeat the Lunatic Cultist, the Clothier will sell the Solar Cultist Hood and Solar Cultist Robe during the day, and the Lunar Cultist Hood and Lunar Cultist Robe during the night.

Behavior
The cultist starts off by warping to a new location and then unleashing one of three attacks: A burst of three homing fire balls which will explode on impact, an ice ball wich emits ice shards in six directions as it flies, and an energy orb wich fires bolts of lightning to player. These are Lunatic Cultist's direct form attacks.

As Lunatic Cultist gets damaged, it will begin attacking with two spreads of five destructible ancient light projectiles as part of his previous cycle.

Occasionally, Lunatic Cultist will attempt to spawn illusionary duplicates of itself. Unless the summoning ritual is interrupted by attacking the Lunatic Cultist and not one of the illusions. These phantoms will stay, flying in formation and adding their homing Shadowflame attacks to Lunatic Cultist's. This will also result in the summoning of a Wyvern-like Phantasm Dragon, and if there is already a Phantasm Dragon inbound, an Ancient Vision, which looks like a miniature version of the Moon Lord's head. These phantom duplicates can be eliminated by interrupting the ritual again, but if not, the Lunatic Cultist can amass a large quantity of phantoms, making the fight much more difficult.

The Lunatic Cultist will go through an attack cycle between each summoning ritual, performing four or five attacks before proceeding. This cycle is repeated throughout the battle, and can become chaotic unless the Lunatic Cultist's summoning rituals are properly interrupted.

Also, in Expert Mode, the Lunatic Cultist will spawn ancient devices which shoot 4 purple projectiles after a while.