The Grim Adventures of Billy and Mandy (2001) : 7x2

When Grim leaves the house to meet someone he met on the internet, Billy looks inside Grim's trunk for something to entertain himself. Billy finds a magical talking Rubik's Cube, which releases the demon Pinface, who has bowling pins in his head. Pinface proceeds to call his minions to conquer Earth, but the minions are more interested in throwing a house party. It is revealed that Grim and Pinface already know each other, and Grim even broke up with Pinface's sister. Billy's father ends up cheating and solves the magical cube by rearranging the stickers, trapping Pinface and his minions inside it again.