In ancient Greek mythology, the Empusa (or Empousa) was a female supernatural monster or demoness. Hecate sent Empusa to harass travelers. It scared to death or ate anybody that traveled along the paths or roads it inhabited. The Empusae are sometimes described as having donkey-like features. They were believed to usually appear with one leg of brass and the other of a donkey. (Aristoph Ran. 294, Eccles. 1094.) Whenever a traveler addressed the Empusa with insulting words, it would flee and utter a shrill sound.
Empusa can be found roaming in packs in Ichigaya field and at night in Ikebukuro. They appear as enemies in Suginami's Diaspora instance and within the Electric Corridor instance as support for Hecate.
Persona 2: Eternal Punishment
"Hecate's servant in Greek lore. Has a donkey's leg and a bronze false leg."
—Persona 2: Eternal Punishment Profile
Known as Empusas, she serves as the first boss encounter of the game along with two Apep. All three can easily be one-shotted using the Earth Rise Fusion Spell.
Persona 3 FES
"A vampire of Greek myth, known to serve the goddess Hecate. She appears as a beautiful woman, but her true form is an evil spirit that drains men`s energy. They feed on human flesh."
