|Series||The Grim Adventures of Billy & Mandy|
|Cartoon Network US Premiere||October 1, 2004|
|Paired with||Super Zero|
Sick of Mandy's bossy and domanering attitude, Grim and Billy place "The Mask of the Beast" on Mandy's face. Those who wear the mask must be kind and nice, or else every act of unkindness will cause the mask to transform the wearer into a monster, step-by-step. When Mandy is informed that she must be 'friendly', 'kind' and 'courteous' to eveyone, or else the mask won't come off, what chance does she have to be returned to normal...
- Story by: Maxwell Atoms
- Storyboard by: Celia Weiss
- Art direction: Rae McCarson
- Directed by: Robert Alvarez, Phil Cummings
- The "monster" Mandy turns into is a combination of a hippopotamus, crocodile/alligator, bear, donkey and iguana. At the end of the episode, she moos like a cow.
- On the TV, a reference to Codename: Kids Next Door is heard when you hear a Australian kid (Numbuh 4) asking Numbuh 3 to go to the treehouse, and clean Numbuh 2's room before Numbuh 1 gets back