The Empusa is a shapeshifting creature of the night, though she also appears at midday. She is an eidolon, an illusory phantom, with an appetite for the flesh of her victims. All of which aligns well with the Titaness Hekate, who is sometimes the mother of Skylla, and often associated with ghosts and haunts.
The Empousa appears in The Frogs by Aristophanes and may have had a role in the Eleusinian Mysteries, which may stem from her association with Hekate. She can appear as a cow, mule, woman, or a dog. With the exception of the mule, Hekate can appear as any of those animals according to lore. In each of these roles, the Empousa is a fearsome creature who resides in the underworld, another connection to Hekate, who is sometimes known as the Queen of that realm. The Frogs puts Empousa in Hekate’s train, a creature bound to Hekate’s will.
Some scholars believe that Hekate and Empousa began as one, with the monstrous creature being an epithet for the Goddess. Yet, Empousa is also described as a vampire-like daimon who will devour her victim. Most surviving stories suggest that the Lamiai, including Empousa, were used as boogy-men, to scare children into following rules.
Hekate and Empousa share an underworldly nature, an association with the Dead, with the same figures of cow, woman, and dog, as well as both wearing bronze sandals, and being an, at times, fearful figure. It is no surprise that scholars believe that they, at the very least, have some common origin.
Who haunts the day and night,
Come forth from the Underworld,
You who attends the sacrifices for the Dead,
Stay your hand from those I love,
And be kind,
And many will be the offerings poured in your honor,