Lunatic Cultist

There is no summoning item and no boss spawner. Once Skeletron and Golem are both dead, a small group of robed cultists gathers outside the dungeon entrance around a glowing tablet. Kill all four and the boss forms in their place. Before Skeletron falls, the Old Man occupies that spawn and the cultists never appear at all, and if you strip the ground out from under the entrance they cannot appear either.

It always materializes at the dungeon's original entrance, wherever that was before you built over it. Drag the four cultists elsewhere and kill them there and the boss still spawns back at the entrance, then despawns because you are nowhere near it. It targets every player and gives up when the last one gets too far, so mirroring out mid fight ends the attempt. Losing is not a soft reset either: the cultists take half an in game day to gather again.

It cannot be hurt while the summoning animation plays out. Once the tablet breaks it rises, laughs at you, and blinks into the air above you. From then on it teleports to a fresh position over your head between every attack, so any lock on target you had is dropped each time it jumps. The attacks come out in a fixed order, so the first attempt is the only one where the sequence surprises you.

• Fireballs arrive as a tight burst, home in on you, and explode on contact with you or with terrain, leaving you burning.
• The ice mist ignores walls entirely. It spins toward you and periodically throws out a ring of shards, and each ring locks to the angle it launched at, so the spinning tells you nothing about where they will go.
• The lightning orb parks itself above the boss and drops bolts on whatever spot you currently occupy, but only while it can see you. Break the sightline and the whole channel is wasted.
• The ritual, the only part of this fight that is actually a puzzle.

For the ritual it vanishes and comes back as several identical copies standing around a rune. Hit the real one and every copy it has made disappears immediately. Hit a fake and the ritual ends on the spot but still pays out, dropping a Phantasm Dragon into the middle of the rune, or an Ancient Vision if a dragon is already alive. Ignore it for a few seconds and the ritual finishes by itself and you get the dragon anyway.

Every copy that survives becomes invulnerable, flies in formation with the real one, and adds a homing shadow fireball to each attack in the rotation. They accumulate, up to six, and they all take part in later rituals. Letting them stack is how this fight turns from readable into chaos.

Picking the genuine one out is the whole skill. Its eyes are narrow and hostile where the copies have blank round ones, it has a line across the hood they lack, and it gives off no light of its own, which is easiest to see at night. When the ritual starts it is the copy standing furthest from you, and hovering the cursor over a fake shows a placeholder value instead of real health. Autopause gives you unlimited time to check.

While a ritual runs the health bar hides, and homing weapons and minions refuse to aim at the real one. If you are running lifesteal, attacking a decoy on purpose is defensible, since the dragon it produces is long and full of health to drain.

Below half health its defense drops sharply and the rotation changes. Volleys of ancient lights get added: slow projectiles that drift through terrain, hang in the air, and detonate on contact or after long enough. They have health, so you can shoot them down, and that also means your homing weapons and minions will happily throw themselves at the lights instead of the boss.

In Expert and above, that same threshold introduces a replacement attack. Instead of a normal move it scatters destructible orbs through the open space around you. Ignore one for seven seconds and it fires four heavy projectiles along the cardinal directions, which in Master ends a run outright. The odds of getting this instead of a regular attack climb again at a third health and again at a quarter, and every surviving decoy adds more orbs per cast. They only appear in open space, so a cramped arena spawns fewer but leaves you nowhere to dodge the crosses they make.

Homing weapons are the wrong pick twice over. It takes reduced damage from them by design, and during rituals they will not aim at it at all. Fireballs and lightning both stop at solid blocks, so a stone shelter plus something that reaches through walls, a yoyo being the obvious answer, removes most of the pressure. The ice mist is the one that still finds you in there.

The lunar events begin the instant it drops. Four pillars land across the world and there is no way to send them home short of clearing all four. Do not kill this boss as an experiment. A pillar frequently lands close enough that you are already inside its spawn radius, so if the background changes, grab the drops and mirror out.

It is not worth farming for loot. There are no weapons, accessories or materials in its table, just potions and the Ancient Manipulator, which you need once. The only reason to kill it again is to run the lunar events again. The Clothier also opens up a pair of outfits afterward, one sold by day and one at night.

• No boss in the game is smaller, and none of the others arrive without a warning message first.
• Its music starts before it spawns, which makes farming the music box unusually painless.
• Each attack echoes one of the four pillars: fire for solar, lightning for vortex, the projectile tricks for nebula, the cloning circle for stardust.
• The mask is a plague doctor's beak, and the word lunatic came from the old belief that the moon caused illness, which fits the moon themed events it unleashes.