Grim & Evil (2001)

Little Rock of Horror / Dream a Little Dream - S1-E13

Continuity mistake: In Dream a Little Dream when it shows Grim, Billy and Mandy eating the pizza, the box is empty. But when they wake up, there is one slice left.

Hoss Delgado: Give it to us straight, Goodburger. Is our little Remus.
Mandy: Billy.
Hoss Delgado: ...Billy, on the bullet train to Smartsville, or is he riding the slow pony to the rubber forest?

A Grim Surprise / Beast and Barbarians - S1-E9

Trivia: In "A Grim Surprise" when Billy and Grim are in the closet, and Billy is telling Grim about throwing Mandy a surprise birthday party, if you look closely at the boxes behind them, one of them has the word "die" written on it. (00:09:20)