|“||It is not enough that I succeed, others must fail.||„|
Mandy is the deuteragonist of The Grim Adventures of Billy and Mandy series. She is 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 - 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 person foolish enough to get on her bad side.
In history between Grim Adventures of Billy and Mandy and Underfist, due to the lack of president in the United States, elections are held to elect a new president. Mandy is presented and manages to win. After that, she sends transfer the Dome of the White House to her own house in Endsville, turning his home into the New White House. She also changes the design of the Flag of the United States for a style more to her, with pink and yellow stripes and replacing the 50 stars on a blue silhouette of his face and name to Billy and Grim as her mad scientists, building a laboratory under her home. As is shown in the episode "Mandy Merciles" it is known what would happen after.
In said episode, Billy, Mandy, Grim and Irwin decide to look into the future for fun because they are hot and bored. Soon Billy, Grim and Irwin will regret having done so because in the future Mandy rules the world in the dark form of an immortal hybrid half human half worm demon, leads an army of current Mandy-resembling robots and creates mutants for combat resistance. Grim is still her "best friend" but also her right-hand and she has created a complex line Billy's clones. Mandy tells one of that "Billies" that, in the past, she discovered in their research that combining his DNA with a worm she would be immortal. Mandy's source of power is cinnamon and she has enslaved humanity to extract it of her mines. She lies to Billy about cinnamon's only weakness saying it is the frogs. Grim leads Billy into the team of resistance against Mandy, and Billy tells them about the frogs, leading them to attack her with them and getting arrested by Mandy. Mandy sentences Grim to the worst of his systems torture for treason and winks devilishly knowing that current Mandy is seeing her.
- Mandy has a couple of similarities to Gaz from the Nickelodeon series Invader Zim.