Heloise is a super-intelligent and destructive 14-year-old (turns to 15 in season 2) girl. Her mad scientist mind and penchant for chaos is hidden behind a facade of a diminutive sweetness. She is one of only two human characters and works for Lucius by creating weapons of mass destruction.
Heloise has green hair and dark teal eyes. She usually wears a red dress that terminates in a curled point. She does not appear to possess legs, they are always hidden. In one episode, Jimmy makes a reference to her "nonexistent feet", but in Something About Herman, when she dressed like her cousin, she was wearing pants, which shows that she does have feet.
Heloise shows that she is intelligent, confident, selfish, crafty and brutal
. She enjoys her position as the Head of R&D (research and development) at Misery Inc. where she makes products to cause misery. Even though Heloise seems like she's brutal, crafty, and a bit of prankmaster, Heloise has shown a good side to her personality as she can be a very loyal, considerate, kind, romantic, and a good friend. She's very sensitive when someone teases or makes fun of her and will often react with rage especially when people call her a little girl. Heloise is the bravest and strongest character as she seems to fear nothing.
In the second season Heloise seems a more happy, cheerful, and bubbly, yet she still retains her sadistic ways. She smiles more in the second season while in the first season she was sarcastic. Her Aunt Pomegranate gave her the girly nickname in Whats Up with Heloise?, Poppy is what her aunt called her.
When someone gets in her way or makes her angry enough, Heloise will often try to destroy them like in the episode Panda-Monium where she tries to get rid of the pandas by showing them how evil she is.
She has a super hero identity as Trouble Bubble Girl, she wears a pink skirt with a white shirt and pink mittens. With her hair colored pink, purple glasses, pink heart shaped earrings, wand, and a tiara. She has a scepter that blows various types of bubbles that has the power to explosives or to levitation. She was appeared in The Terrific Trio with Jimmy and Beezy as Power Squid and Spaghetti Beezy.
Heloise has had massive crush on Jimmy since the beginning. According to series creator Edward Kay, she fell for him because "there's something about sweet, innocent guys that appeals to the last shred of humanity in her." She has made numerous attempts to win his heart, but Jimmy remains oblivious to her affection, despite her lack of subtlety in the regard.
The depth of her crush on Jimmy is shown in the episode "Fused Together", when Dorkus discovers she has a shrine to Jimmy hidden behind a bookcase, which is triggered by pulling a lever next to it. She quickly made him forget by pulling out his brain, slapping him with it, and then throwing it away. The shrine appears again in "Best Bud Battle" and "Pet Rocky", though in the latter it's behind the fireplace. She also showed her affection in "Jimmy MatchMaker" at the grand opening of Lucius' statue. There, Heloise was whistling and trying to signal that she and Jimmy should hang out together. As usual, Jimmy failed to get the message. In the second season she continues to attempt to to get Jimmy's attention in many moments by trying to look cute to Jimmy. She even protects Jimmy like in the episode Heloise's Rival when Mean Jean challenges her to trick, scare, and harm him but Heloise doesn't want to and in the end she beat Mean Jean and protected Jimmy from being thrown across the city. In Better Sweater she made a blue love sweater for Jimmy, it didn't work at first because he put on the fear sweater instead, but when he had it on he was totally affectionate to her and said "I can no longer hide my feelings, I adore you" so he really did admit he likes her, and he was jealous when Heloise dated Peep in Heloise's Secret Admirer.
They are frenemies in the show. Beezy finds her boring and serious while Heloise just thinks of him as quirky, disgusting, and annoying. But in some episodes they get along, in Pet Rocky she helped him get his pet back and in Dance Jimmy Dance they went to a dance competition together. Despite her dislike of Beezy, she tolerates him only to be around Jimmy. Beezy shares the same feeling of resentment, not liking the competition for Jimmy's friendship. Despite this, the pair accidentally kissed once to eachother's disgust. Heloise doesn't really like any Henious.
Heloise seems to take more of a liking to Cerbee. This is probably evident in the fact that Heloise finds Cerbee cute when trying to tell her something in "Jimmy in the Big House", using him as a power source for the snow machine in "A Cold Day In Miseryville' and even willing to help him when it come to love in "Cerbee In Love". It is also undoubtedly true that Cerbee likes Heloise, which is very evidently proven by the fact that Cerbee has never eaten or even tried to bite Heloise.
In "Heloise's Secret Admirer" Heloise dated Peep to get Jimmy jealous. Peep actually has an enormous crush on Heloise as is shown in his first episode "Everyone Can Whistle", he usually always attempts to flirt with her to little success when she's around.
- Heloise was voiced by Tabitha St. Germain.