frown, although her expression will change in rare occasions when she is afraid or disgusted. Her outfit consists of a pink dress with a picture of a yellow flower on it. She rarely smiles and is quick to deny it when she does. She is not above taking advantage of the stupid (usually Billy) and on several occasions has been described as pure evil; Grim refers to her as a "horrible demon child".
She can easily intimidate inferior people into doing anything for her (with the possible exception of Billy's Mom), and even her parents fear her. While she treats Grim and Billy horribly, there have been indications that she does care about them and does consider them her friends. She is shown as almost completely fearless, rarely even flinching when facing monsters and other creatures. The only thing that she is shown running from in a vague sort of fear is an enraged Billy. However, in one episode Billy comments about her "fear" of professional figure skaters, in which she retaliates, "That's not a fear, I just don't trust the way they spin, is all."
- The first smile Mandy made was in the ending of the first episode.
- In the comic book Grim Tales, Mandy became Grim's wife and became immortal.
- In an episode, Mandy's smile appears to have some effect to reality.