Empousai (singular: Empousa) are winged, bloodsucking monsters under the control of the goddess Hecate. They are known to feed on the blood of men and are the basis for the image of the modern vampire.
Empousai are created by combining together magic, animal, bronze and ghost. They are sent by Hecate to guard roads and devour travelers. According to some records, the Empousai ran and hid, uttering a high-pitched scream at the sound of insults.
The Empousai are best known for their appearance in Aristophanes's The Frogs, in which they scared Dionysus and Xanthias on their way to the Underworld. They originated when Pandora opened the pithos that she was given. When she opened it, the first Empousa was released.
There are two Empousai masquerading as cheerleaders named Tammi and Kelli at Goode High School. Percy manages to kill Tammi with his celestial bronze sword, Riptide, with the assistance of Rachel Dare, a mortal who can see through the Mist and received the power of prophecy from Apollo. Kelli, however, escapes by bursting into flames. The heroes later encounter Kelli in Daedalus' workshop. She brings in the ghost of Minos, Daedalus's arch-enemy, Nico di Angelo, and a few other monsters. She corners Percy after his sword is knocked out of his hand, but she is soon stabbed in the back by Annabeth Chase.
An Empousa holds Prometheus' arm as they approach Percy under a flag of truce. The Empousa mentions that she was one of the spirits released when Pandora opened the pithos containing demons and disease. She later bares her teeth at a Hyperborean giant.
When walking through Tartarus, Annabeth Chase and Percy Jackson spot five Empousai making their way to the Doors of Death. Among the five were Kelli and Serephone. Annabeth tricks Kelli by talking her into killing Serephone. As the empousai are about to kill Percy and Annabeth, Bob the Titan comes and saves them, killing the Empousai with his broom.
The Empousai reappear when Frank Zhang, Hazel Levesque, Jason Grace, Leo Valdez, Nico di Angelo, and Piper McLean are making their way toward the mortal side of the Doors of Death. They are among the countless monsters that attack Frank, Jason, Nico and Piper. The Empousai use their charmspeak to command the other monsters, until Piper is able to use her charmspeak to cause the Empousai to fight one another to the point that they can no longer give commands, allowing the four demigods to destroy them and their army.
Empousai are extremely beautiful and seductive women. However, an empouai's true form is a woman with flaming hair, white skin, red eyes, fangs, one prosthetic celestial bronze leg and one donkey leg, wings, and their eyes glow red . This form is used to drink the blood of the men they enchant.
- True Form: Their true form can paralyze a man just by the sheer sight of them. They use this form to drink blood.
- Mist Manipulation: They can manipulate the Mist.
- Charmspeak: They can charmspeak in order to attract their mortal victims. They have the power to make a man fall under their spell to incapacitate them. In some cases, if the man has enough willpower, like Percy Jackson and Luke Castellan, then he can snap out of the spell.
- Flame Teleportation: Older Empousai apparently have the power to escape in a shower of flames
- Hypnokinesis (limited): Some of them have limited metacognition, as they may know that people are watching them in dreams or visions. This is shown in a scene where Kelli scared Percy out of his dream.
- Shapeshifting: Empousai can shapeshift between their human and true form.
- Seduction: With their stunning looks, they can offer a kiss to the young man in hopes of having him come close to suck on their blood.
The name is said to mean "one-footed." This is because Empousa is one-legged hybrid,
- In myth, the Empousai are the beautiful daughters Hecate and the spirit Mormo. They feast on the blood of seduced men as they slept.
- In the graphic novel, their eyes are fiery yellow, though in The House of Hades and The Battle of the Labyrinth, their eyes glow red.