Mrs. Jötunheim is a short, elderly-looking woman. Her skin is green and wrinkled, and her gray hair is held up in a bun. She has a large, lavender nose, and slightly pale lips with two blunt teeth sticking up out of her bottom lip. Her left eye is shown to have a yellow iris. She wears a purple dress and two rows of golden bangles on both of her arms. Along with her sagging breasts, her body is shown to be very short in stature, as both Gumball and Darwin are taller than her.
Behind her superficially grumpy manner and the fact that she is a witch, Mrs. Jötunheim is shown to not have malicious intentions and preserves mature principles. For example, when the troll is released from the Door of Forbidden Secrets, Mrs. Jötunheim guides Gumball's effort in defeating the Troll and lends him some magic powers, as well as a wand. In "The Potion," Mrs. Jötunheim refuses to shrink Hector into normal size, out of the idea that "no potion will make you accept who you are."
Mrs. Jötunheim is very protective of her son, choosing what movies he should watch and what comics he should read. In "The Colossus," it is later revealed that she has a very good reason for doing so, since, as she later explains to Gumball and Darwin, literally everything about a giant is big, including their emotion— as a result, they have to be kept as calm as possible. She initially has a confrontational attitude towards Gumball and Darwin but does not seem to blame them when Hector begins destroying the town (even though it was at least partially their fault).
- "The Colossus": Her first major role. She is overprotective of Hector.
- "The Castle": She attends Richard's party.
- "The Finale": She comes to receive money that the Wattersons owe her and Hector, and is later insulted by Nicole to make Hector mad.
- "The Name": She is seen in line.
- "The Mirror": She makes a potion for Gumball and Darwin to repel the Snatcher.
- "The Others": She is in a thought bubble.
- "The Routine": She predicts the future for Richard.
- "The Night": She is knocked off her broom by Gumball in his dream.
- "The Compilation": She sings "Weird Like You And Me."
- "The Sorcerer": Her second major role. She teaches Gumball and Darwin how to be wizards.
- "The Singing": She sings part of "I'm Singing."
- "The Nuisance": She is lying on the ground when the fire is going in the sky.
- "The Anybody": Clayton steals her broomstick.
- "The Candidate": She appears at the charity event.
- "The Shippening": Sarah ships her with Hank.
- "The Intelligence": She tries to dunk Mrs. Robinson for being a witch while hiding the fact that she herself is a witch.
- "The Potion": Her third major role. She refuses to allow her son to drink a shrinking potion and accept who he is.
- "The Ghouls": She sings "All Hail All Hallow's Eve!" and says she gets to wear a weave.
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- Her design is a homage to the character Yubaba and as well as her younger twin sister Zeniba from the Studio Ghibli film Spirited Away.
- Both Yubaba and Mrs. Jötunheimr are witches, and they both have gigantic, destructive sons.
- Her right eye is gray, indicating that she may be blind in that eye, or have a glass eye.
- However, when she takes off her makeup in "The Castle," both of her eyes are gray, revealing that it is simply her natural eye color.
- In Norse mythology, Jötunheimr is the homeland of the giants, which is fitting because of who and what her son is.
- In "The Singing," it is revealed that she is only twenty-eight years old despite looking much older.
- It is revealed in "The Colossus" that she owns at least three magical brooms that are capable of flight, similar to witches of legend.