Lunatic Cultist

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

Behavior
The Lunatic Cultist starts off by warping to a new location and then unleashing one of three attacks: a burst of three homing fire balls which explode on impact, an ice attack which emits ice shards in six directions as it flies, and an energy orb which fires large bolts of lightning at the player. This is the Lunatic Cultist's direct form of attack. As the Lunatic Cultist becomes damaged, he will begin attacking with two spreads of five destructible ancient light projectiles as part of his previous cycle.

In Expert mode The cultist may spawn numerous Ancient devices which will shoot 4 Purple projectiles In a Plus sign after a while.

Occasionally, the Lunatic Cultist will attempt to spawn illusionary duplicates of himself. Unless the summoning ritual is interrupted by attacking the Lunatic Cultist and not one of the illusions, these phantom duplicates will stay, flying in formation and adding their homing shadowflame attacks to the 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.

Tips

 * Avoid defeating the Lunatic Cultist if you are not yet ready for the Lunar Events, as after beating the Cultist the Lunar Events begin immediately, and there is no way to de-summon them (aside from defeating them). Take care that any minions/NPC's in the area don't kill the Cultist inadvertently.
 * Attacking the decoy cultist is not a bad idea if you have Vampire Knives. The Phantasm Dragon is very long and you can easily regain some life by hitting the Dragon with a wide barrage of knives.

Trivia

 * It is a common belief that the Cultists' design was inspired by Crowno's clothes. However, according to Crowno, the Cultists were designed before it.
 * The boss' appearance resembles a plague doctor costume, which was a garment worn by physicians who treated the Black Plague in 14th century Europe.
 * It is the smallest boss, and the only one without an awakening message.
 * The Lunatic Cultist's mask and trophy are named "Ancient Cultist" rather than "Lunatic Cultist", as they are still using an early development name. Several other enemy drops from 1.3 also retained their early development names until later patches.
 * If Skeletron isn't defeated in a world but Plantera and Golem are, then it is possible that the cultists won't spawn making it impossible to spawn the lunatic cultist.
 * The Lunatic Cultist has an Expert Mode Treasure Bag in Terraria's game files, but it is currently unobtainable as he does not actually drop it.