Mandy is a cynical and arrogant girl with blonde hair with a black hairband, black shoes, and a light pink dress with a yellow flower on it. Mandy, unlike Billy, is smart and loves absolute power, order, chaos, and control, which is something she uses to make Grim her obedient servant and slave. Billy and Mandy are best friends, although sometimes it is hard to tell.
It has been stated many times throughout the show that Mandy never smiles--she always maintains an angry facial expression. Although many times she grins when she's done something mean to someone else.