Billy and Grim mistakenly deduce that Mandy is a cannibal and has eaten everyone in the neighborhood! Billy decides to confront Mandy before she eats him! Billy's mom returns, bent on taking vengeance on Grim.
In "Big Trouble in Billy's Basement" Billy steals Grim's "bad book" and starts an apocalypse, which Mandy, Grim, and Hoss Delgado must stop. In "Tickle Me Mandy" Mandy goes away for a day, so Grim makes Billy a new Mandy to play with.