An optional boss in Terraria, found after defeating Plantera. Resembles an attractive Fairy with a Tiara and Butterfly Wings. Killing the Prismatic Lacewing summons her as revenge for killing the critter. Notably, fighting her during the Day will make her be able to kill you with a single hit, but you do get a unique weapon, the Terraprisma (Terraria), by beating her in that time.
According to the developers, the Empress's attacks and music are directly inspired by Touhou Project and other bullet hell games.