Mandy (The Grim Adventures of Billy & Mandy)

"It is not enough that I succeed, others must fail" ~ Mandy

Although one of the main characters in the dark cartoon series known as the Grim Adventures of Billy and Mandy, the titular Mandy is far from your usual protaganist, in fact she is shown to be a very evil individual who never smiles (in fact when Mandy smiles it has cataclysmic effects): she treats everyone around her with contempt, especially Grim and Billy (Billy and Mandy)- though she does seem to see Billy as a friend of sorts.

Mandy appears to be a little girl but is often shown to have an almost supernatural power of her own, it is suggested in some stories she may even be the embodiment of evil itself (though this is never proven), Mandy is capable of terrifying people with a mere glance and tends to display little to no emotion outside her usual contempt.

Mandy seeks to someday rule the world and hates being restrained - in fact trying to restrain Mandy is probably one of the most ill-advised things a person can do as, despite her cold and often emotionless exterior she is more than capable of coming up with plans for revenge on any foolish enough to get on her bad side.

Trivia

 * In the show, Mandy was sometimes called "Mechanical Fiend".