Nergal Junior (Junior), is the son of Nergal and Billy's aunt Sis, and Billy's maternal first cousin. He has the ability to shape-shift, and has tentacles protruding out of his back, not unlike his father. He also possesses the capability to take the appearance of human beings he chooses in order to impersonate them as well as the ability to freeze them in a state of suspended animation. Junior, is referred to as a Nergal, which is a shapeshifting demon from the center of the earth. His mother, however, is human, making him a hybrid of sorts. It is never clear what exactly his true form is, for it has never shown on screen, but it can be assumed it is not pretty as it is said to be the most horrible thing seen by humans. Because of his natural appearance he assumes the form of a little boy (nameless) he ran into in "Son of Nergal", it can be assumed that the little boy is still frozen in ice near the campgrounds to this day. When he takes another shape, he keeps his lime eyes, glasses, green tongue, and sharp, yellow teeth, and when speaking in a disguise it sounds like him, and the person he is shaped as talking at the same time. Junior has an introverted personality. He has become used to people avoiding him and usually assumes the worst of other people, despite this, he, like his father, wants to have friends, though he can't seem to keep them longer than an episode. Because of his desperation, he developed evil tendencies and terrorizes everyone who stands in his way, except for Billy and Mandy. An example of this is the fact that he captures Sperg and made him his "pet", and sticking his teacher to the ceiling. Junior's only friends are Billy, Mandy, and Irwin. Billy was his first friend, but after seeing Jr.'s true form was frightened and briefly frozen for an episode. His only natural enemy is Sperg, the school bully who picks on him despite the obvious fact that he could send Sperg into a swirling vortex of doom for eternity. Junior can shapeshift into any shape and form he desires at will, and electrify enemies by ensnaring them in his snake-like tentacles.