
Amanda "Mandy" is the titular tritagonist of The Grim Adventures of Billy and Mandy series. She is, in fact, shown to be a pretty vile individual who rarely smiles (in fact when Mandy smiles it has cataclysmic effects). She treats everyone around her with contempt, especially Grim and Billy, though she does seem to see Billy as a friend of sorts.
She was voiced by Grey DeLisle, who also voiced other villainesses such as Azula, The High Priestess, and Vicky.