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 in defending you/themselves.
 * Shooting 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 Cultist's design is inspired by Crowno's Developer Armor. However, according to a profile post of his in the forums, the Cultists were designed before it.
 * The boss' appearence 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 boss without an awakening message, and the only character in the game that speaks (it chants incoherently when summoned, and when summoning a Phantasm Dragon).
 * The word lunatic comes from the Latin luna, because it was believed that people were more likely to exhibit aberrant behavior during a full moon. This may explain why the Lunatic Cultist is involved with the Lunar Events.
 * The Lunatic Cultist seems to drop the "Ancient Cultist Trophy" rather than the expected "Lunatic Cultist Trophy." Likewise, it drops the "Ancient Cultist Mask" instead of a "Lunatic Cultist Mask."
 * The boss' attacks (using ice, fire and lightning attacks as well as summoning monsters) and overall fight is quite similar to numerous boss fights from the CastleVania series, such as Barlowe or Shaft.
 * 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.
 * Many of its attacks are seemingly based on others in the game (e.g. the Lightning Bolts being fired from an object that looks like the Magnet Sphere, or the Ice it fires appearing to be the same as that fired by the Ice Queen).
 * The Lunatic Cultist is one of the only, possibly the only boss that does not drop a Treasure Bag in expert mode (Apart from bosses in events and invasions like the Frost Moon, Pumpkin Moon, Goblin invasion, Pirate Invasion, Martian Invasion, and Celestial Events), however there is a Treasure Bag in the game's code although it currently is not in use it is unknown if it will be added as a drop in a future update.
 * The Lunatic Cultist attacks also resemble the diffrent Celestial Towers, The Fire attack repersents the Solar tower, The Ice represents the cold of the Nebula Tower and its spawn, The Lightning represents the lightning from mobs in the vortex Tower, The Dragon and The clones represent the Summons from the stardust Tower.

History
Cultiste Lunatique Lunar Cultist