Penny is short, with a round face, stubby legs, and no toes. She has short red hair and, like most characters on the show, black dots for eyes. Penny has various bruises, scrapes and dirt smudges on her chubby, round face, which may be the mark of a thief. She is short and is almost as tall as Jake. She wears tattered and torn clothes. She looks as though she is poor, but has many stolen treasures; her deceiving appearance probably helps when tricking others. She may actually be older than she appears, as suggested when she said, "I haven't felt like this since I was young!" after Finn and Jake purified her. Her skin color is officially referred to as peach.
On the outside, she is a cute, harmless baby girl, but on the inside, she's a thief and a trickster. She uses this to her own advantage to trick and steal from other people. Her defense is a sharp, black kris dagger, and a shotgun was seen in her old tent.
She lives inside a battered tent in the middle of the City of Thieves, and her tent is where she keeps all of her stolen treasures. It is also invaded by Finn and Jake when they come to "purify" Penny. At the end of the episode, Finn and Jake give her a bath and vigorously wash off the muck and filth that marks her as a thief with soap. However, she becomes a thief again when she steals Finn's clothes, and she doesn't really change her ways.
- Pendleton Ward has stated that Penny is not human, due to her having huge cheeks, and that she is actually a "peach-colored mutant."
- She hides a black kris dagger in her raggedy gray cloak.
- She was originally intended to return in "I Am a Sword" as shown in concept art, but this was scrapped as she was replaced by Bandit Princess, most likely because Penny's voice actress was unavailable.
- She seems to have stolen a double-barreled shotgun, as seen in her tent.