Empusa or Empousa (ɛm'pjuːsə; Ἔμπουσα; plural: Ἔμπουσαι Empousai) is a shape-shifting female being in Greek mythology, said to possess a single leg of copper, commanded by Hecate, whose precise nature is obscure. In Late Antiquity, the empousai have been described as a category of phantoms or spectres, equated with the lamiai and mormolykeia, thought to seduce and feed on young men. The primary sources for the empousa in Antiquity are Aristophanes's plays (The Frogs and Ecclesiazusae) and Philostratus's Life of Apollonius of Tyana. The Empusa has been defined in the Sudas and by Crates of Mallus as a "demonic phantom" with shape-shifting abilities. Thus in Aristophane's plays she is said to change appearance from various beasts to a woman. The Empusa is also said to be one-legged, namely, having one brass leg, or a donkey's leg, thus being known by the epithets Onokole (Ὀνοκώλη) and Onoskelis (Ὀνοσκελίς) which they mean "Donkey-footed". A folk etymology construes the name to mean "one-footed" (from Greek *έμπούς, *empous: en-, one + pous, foot). In Aristophanes's comedy The Frogs, an Empusa appears before Dionysus and his slave Xanthias on their way to the underworld, although this may be the slave's practical joke to frighten his master. Xanthius thus sees (or pretends to see) the empousa transform into a bull, a mule, a beautiful woman, and a dog. The slave also reassures that the being indeed had one brass (copper) leg, and another leg of cow dung besides. The Empusa was a being sent by Hecate (as one scholiast noted), or, was Hecate herself, according to a fragment of Aristophanes's lost play Tagenistae ("Men of the Frying-pan"), as preserved in the Venetus. By the Late Antiquity in Greece, this became a category of beings, designated as empusai (Lat. empusae) in the plural. It came to be believed that the spectre preyed on young men for seduction and for food. According to 1st century Life of Apollonius of Tyana, the empousa is a phantom (phasma) that took on the appearance of an attractive woman and seduced a young philosophy student in order eventually to devour him.