6x19 - The Grim Adventures of Billy and Mandy

When Mandy says even a trained monkey is more competent to do cleaning chores than Grim, and would complain less, Grim makes Dickie Galoot, a monkey appearing in a Japanese-styled animation, come to life to prove her wrong. As Dickie turns out to be extremely good at cleaning Mandy's house, Grim decides to leave the kids for good. Due to his friendship contract, Grim is unable to break free, and he is forced to battle Dickie to recover his place as the "cleaning monkey" of the group. Grim successfully defeats Dickie at cleaning Billy's house, but this all turns out to be an ingenious plan devised by Mandy to win a bet against Billy.