Her cruel nickname supposedly comes from smelling like recycled water used to cook hot dogs, and is allergic to gluten. Her brown hair is usually very curly-loose-waves-messy.
Originally she was very competitive with Velma Dinkley and they had a strong mutual dislike. This may have changed, however, when they bonded after both working for Mr. E. The issue is still open because Marcy reported to Mr. E. that she had Velma "right where I want her." She is good with computers, and a brilliant amateur chemist. She's First appeared in Meeting Gumball and Darwin.