Mandy started off as the boss of her own 'friend'/slave, Grim, after winning a bet involving a Limbo competition. She has a cold-hearted and evil personality, yet later on, she starts to develop a strong bond with Grim. She is one of the most intelligent, if not the most intelligent being the series' universe. She was the one who reminded Grim who he really is; The "Grim Reaper", and out of graditude for not killing her when they first met, Mandy freed Grim from their deal. As she grew older she became beautiful, deadly, and rich. Grim lets her live as a temporary inmortal being and she becomes the mayor of the city called Megaville and a very tough assassin. This later on results in Grim asking her hand in marriage. She agrees and becomes an eternal being. Then she becomes Queen of the Underworld and is the most feared character in the Grim Tales Universe. She and have Grim have two children: Grim Junior and Minniemandy (Minnie for short). Both children are very unlike their mother. Their adventures are similar to what she and Billy had in the past.
Mandy is still as bossy, mean and demanding as she ever was and she has earned the nickname The Queen Bitch. As revealed in the Powerpuff Girls Doujinshi, Mandy attended school with the Power Puff Girls, but did not help Blossom when Him came to destory Megaville. Even Grim commented that she should have helped her old friend, but Mandy reminded him that she has no friends. When the daughter of Blossom and Him, Mimi, intruded into her personal volt, Mandy attacked and sucked the evil right out of Mimi. She also forced Mimi into reliving her worst nightmare, the day her father came for her and destroyed almost everyone she loved. Ever since the intrusion of volt, Mandy has been planning to go to war with Him and has been seething with anger at Him ever since.