|“||You don’t even know what’s happening, do you? Soon, your pretty little camp in flames, your friends made slaves to the Lord of Time, and there’s nothing you can do to stop it. It would be merciful to end your life now, before you have to see that.||”|
In Percy's dreams, Kelli always sensed that he was watching. She tries to bite him every time, causing Percy to wake up.
Kelli and a group of other empousai are walking towards the Doors of Death. Kelli talks about how when they get to the mortal world she wants to personally kill Percy. Eventually, Percy and Annabeth defeat Kelli and the empousai, with the help of the former Titan Lord of the Underworld, Iapetus (now known as Bob).
While pretending to be a normal cheerleader, Kelli is an alluring valley girl, but is cruel and merciless in her true form.
Kelli is an empousa, who are the servants of the goddess Hecate. In true form, she has completely white skin, flaming hair, fangs, one bronze leg and one donkey leg, and red eyes. When in human form she appears as a pretty African American girl with curly hair. Percy describes the hair as "curly hair like Medusa's".
As an empousa, she can put men under her spell so she can feast on their blood. She can also charmspeak, change shape, and manipulate the Mist, as stated by Annabeth in The House of Hades. She can change from her human form to her true form. She is also able to sense demigods watching her in their dreams as she scared Percy out of his.