Empress of Light

There is no summon item you craft for her. She arrives when you kill a Prismatic Lacewing, a critter that only turns up on the surface of the Hallow between dusk and midnight, and only after Plantera is dead. Killing one where you find it means fighting her there, at night, on ground you did not prepare. Net it with a Bug Net and walk it to an arena you built instead.

Released outside the Hallow it vanishes in a second or two, faster than most people can swing. Drop it into something already dealing damage in place, a Clinger Staff flame pillar or a Rainbow Gun beam, and the summon lands every time.

She has no progression gate of her own. Only the lacewing needs to exist, which is why a jar of captured ones can be carried into a fresh world and used to fight her absurdly early. That cuts both ways: clip a butterfly you were not looking at while working the Hallow, and she shows up anyway. A Guide to Critter Companionship in your inventory blocks damage to critters entirely and is the simplest insurance against that.

If she has taken no damage during the night, she gives up and leaves once evening comes around. If she has, she simply drops out of her enraged state at sundown and the fight carries on. That rule shapes the entire Terraprisma attempt, because the sword only drops when every point of damage you dealt landed in daylight. One stray hit before dawn and the run is spent. Summoning her in the last few minutes before dusk is worse still: she despawns on arrival and the lacewing is wasted.

• Homing bolts. She dumps a spread around herself, either scattered or wound out in a spiral, and they turn toward you after a short delay. Their tracking is imperfect, so a hard change of direction as they close makes them overshoot. Running away in a straight line does not.
• The dash. She lines up level with you on one side, flickers with spinning colored afterimages, then crosses horizontally. The telegraph is generous and she is briefly untouchable while it plays, so stop attacking and start moving.
• Sun Dance. She hangs above you and puts out heavy projectiles that rotate slowly around her in overlapping sets. They do not chase, they occupy space, so leave the space rather than trying to out-dodge them.
• Everlasting Rainbow. A ring that spirals outward then curls back inward along the same path, trailing light that hurts as much as the ring does. The return leg catches people who relaxed once it passed them.
• Ethereal Lances. These are what actually kill you. They materialize around you behind colored beams and do nothing until they fire. Some variants spawn behind your direction of travel, so the punishment is aimed where you were going. Others sweep the screen in waves from alternating sides. Read the beams, never the lances.

Her damage ignores the invincibility window you get after a hit, so two things landing together both land in full.

At half health she vanishes, reappears above wherever you were heading, and comes back with tendrils on her back and a much harder shell. Nothing in her toolkit is new. What changes is the schedule: a different running order, less pause after each attack and a shorter gap between them, so the recovery you had been using to reposition is gone. Expert trims the gaps further, and the harshest world seeds cut them roughly in half again.

She improvises nothing. Each phase runs a set list in a set order on a fixed interval and repeats until one of you is dead, which is the only reason a bullet hell this dense is survivable. Spend the first loop learning what follows what and the fight becomes recall rather than reaction. The one wrinkle is the switch between her ordinary and enraged move sets in the second phase, which can repeat a move or drop you elsewhere in the order.

Fought during the day she is enraged, her projectiles turn yellow, and everything she has kills you outright regardless of defense. Dodge effects do not save you either: Holy Protection, the Black Belt line and the Brain of Confusion are all bypassed, so the defensive half of your loadout is dead weight. She also runs her Expert patterns while enraged no matter which difficulty you are playing.

Swap all of it for damage and movement: hovering wings or a Jetpack, a dash from the Shield of Cthulhu, and the Rod of Discord used without hesitation, since the health Chaos State takes is health you were never going to spend. Campfires, heart lanterns and defensive statues are pointless for the same reason. Nothing here is a survivable hit.

Build long and flat, floored with Asphalt Block and layered with platforms, because you spend the fight moving horizontally at speed. Keep level with her or below her. She repositions above you after nearly every attack, so drifting upward walks you into her body at the exact moment you were dodging something else. She has no useful debuff immunities, so Ichor is real added damage, and homing or long range weapons matter more than raw numbers, since you rarely get to stand still and aim.

• She was described during development as a beautiful bullet hell, and the influence is Touhou and the games around it.
• She is the only boss that enrages by daylight and calms down at nightfall.
• Her gore has blue blood, a joke on noble birth that fits the title. Duke Fishron shares it, along with the critter summon and the themed wings.
• Her internal name is HallowBoss.
• She is optional. Beating her is not required for progression and does not count toward the achievement for killing every boss.