In Greek mythology, Empusa is one of the spectres of Hecate, goddess of the ways. It was believed that Hecate wandered the earth at night, accompanied by her retinue of spectres, seen only by dogs, whose barks indicated her approach.
Some say that the Empusas are daughters of Hecate and Mormo. Spirits so wicked and demonic that they came out of Pandora's box along with all the evils to scare humanity.
The demons functioned as Hecate's soldiers, being sent to solve "special missions". Their way of acting was simple and practical, with their metamorphosed form, they deceived their victims also with their convincingly magical voice.
According to Pierre Grimal, Empusa could metamorphose into a beautiful young woman in order to attract her victims and thus feed herself. Also according to the author, it belongs to the Underworld and inhabits the nights of terrors. She can appear to women and children in various forms to frighten them.
They may also have inspired the legend about vampires, since they fed on humans (more precisely young men who were lured into their beds) with their fangs.