Nergal Jr. is the son of Sis and Nergal, and Billy's paternal first cousin. He has the ability to shapeshift, and has tentacles protruding out of his back and head, not unlike his father. He also possesses the capability to take the appearance of any human beings he chooses in order to impersonate them as well as the ability to freeze them in a state of suspended animation. Furthermore, he is able to take the appearance of any object. He is voiced by Debi Derryberry.