Penny Fitzgerald is a supporting character in The Amazing World of Gumbal and the main protagonist in The Amazing World of Gumball: The Movie and The Powerpuff Girls Crossover. She is an antlered peanut who is in Miss Simian's class at Elmore Junior High. Gumball and Penny have massive crushes on each other, but the two of them struggle to express their feelings. She was part of the treehouse girls' club before it disbanded due to the tree being cut down.
Penny was an anthropomorphic peanut. Like the rest of her family, she has a set of antlers growing out of her head. In season 3, episode The Shell, it is revealed that Penny is a shape-shifting rainbow fairy-like creature. She can transform into any animal, and every time the animal has a set of antlers.
In Season 2, the design of Penny's shell has been altered. Previously, it was straighter and shaped more like her father's shell, but now, it is curved to resemble her sister's and her mother's. Her antlers are also darker and smaller.
Penny does not normally wear much clothing, aside from a pair of orange sneakers, and some red and white arm bands. However, she is often seen carrying white pom-poms.
In "The Shell," the contents of her shell are revealed. She can shapeshift into any creature, depending on her emotions, but her default form seems to be an orange, fairy-like creature with antlers. Her body takes on the shape of her shell, and the upper half of her body gets progressively lighter shades of orange in coloration. She also has wings, which she can use to hover above the ground. According to story writer Guillaume Cassuto, Penny will no longer be in her shell and will remain in her fairy-like form.
Penny is very nice and friendly. She sticks up for her friends often, implying she has a strong sense of integrity.
She is one of the few people to understand Gumball, whom she has a crush on. The feeling is mutual, but neither of them have ever had a chance to properly express their feelings, despite that it is clearly evident, that is until "The Shell".
She has represented independent signs of getting annoyed on occasion, like becoming angered (even resorting to deception) to her father in the episode "The Knights," when he forbid her from seeing the Wattersons, and tiring of the conflict between Gumball and Tobias in the same episode. But, she is exceedingly grateful and ecstatic when Gumball saves her from accidentally getting hit by her father's vehicle, and relieved when she realizes her father is okay as well, showing that she is self-sufficiently forgiving and caring.
She also seems to be athletic, as she is a very good cheerleader, and was/is part of the synchronized swimming club. Also, in "The Dress," she was one of the first people to finish running around the track.
Without her shell, she is very self-conscious, running away at the first sign that someone believes her to be a monster. Even worse, she transforms into said monster as she runs away, fulfilling their expectations.