Grim is bored of being left alone while Billy and Mandy are not with him. Grim decides to fulfill his dream by working as a swimsuit model, but, as he is a corpse, he is not hired. Subsequently, Billy and Mandy give him a makeover to look more human. In the end, Grim gets the job in a TV ad, but he is only in the commercial for a few seconds and is portrayed as an ugly person.

Billy wanders into a junkyard, where a massive hole in the earth opens up and pulls him down in. Later, Mandy and Grim get pulled in as well. They land at the center of the Earth, which is home of Nergal, a devilish creature. The lonely Nergal, who has been watching Billy and Mandy for some time, wants Grim to hand over the kids to him so they can be his friends forever. Grim happily leaves the kids behind as he returns to the surface; however, he later goes back for them because he can't handle the guilt of abandoning his friends. In the end, Grim is defeated by Nergal's electrified tentacles, but Mandy defeats Nergal merely by kicking him in the shin.

While Spring cleaning in the middle of November, Billy takes an old, cursed lamp from Grim's trunk. When he gives it a rub, he releases the curse Grim had warned them about: his own mother. Having three wishes to make, Billy wastes his wish by wishing to know what to wish for. Mandy wishes Billy and Grim would "shut up", so Grim never gets to make his wish. Then, Mandy decides to make the last wish to whoever makes her the happiest. In the end, Mandy wishes everyone in the world would go away, which she is glad about.

Zombies crave the brownies Billy makes.

Zombies crave the brownies Billy makes.

Mandy visits a haunted house.

Billy and Mandy contend with Nergal Jr.

Billy and Grim switch places for a day.

Nergal attempts to woo Billy's aunt.

When Billy forgets to do his history homework, Grim gives him a universal remote control to alter time and space so he can go back in time and finish his report. Billy and Mandy travel to the American Revolution, to prehistoric times, and even to the future, where they meet an aged Billy who is just finishing the report. After a struggle for the remote, Billy ends up again in the Prehistory and the remote breaks. Fast forward into the present, every person is dumb like he is and shares his characteristic big nose, including Mandy and Irwin.

After Grim's robe comes out of the washing machine, Billy and Mandy find Thromnambular, a talking skull with ruby eyes and a number nine imprinted on his forehead. Grim tells them that the skull is a magical artifact imprisoned on Earth that must grant his nine wishes to be free. When Mandy asks Grim why he has not used any of the wishes, Grim tells her that the skull will corrupt the wishes and end up affecting the wisher.