As her name states, she is a very muscular princess. She is green skinned and wears dark blue boots with yellow hearts on them. Although, in the episode, "What is Life?," she is depicted with yellow stars on her boots, and a blue dress. She has a small, yellow crown on her head. She usually carries a dumbbell and works out her arms. In the episode "To Cut a Woman's Hair," it is revealed she has a deep masculine voice. Her hair is short with two heart-shaped buns on each side of her head; she claims her hair looks bad so people will notice her muscles. Her crown, skirt, hairstyle, boots, and lips were redesigned after her cameo in "What is Life?" and she no longer has visible veins which were part of her original design.
In the episode, "Princess Monster Wife," the hearts on Muscle Princess's boots were changed from light blue to yellow and the heart on her crown changed from gold to red. The blue skirt was also lightened to a lighter blue.
In the episode "To Cut a Woman's Hair" Finn called her "Princess Muscles" so she may probably be formaly known as both "Muscle Princess" and "Princess Muscles."