Marissa is a young girl with curly blonde hair and tan skin. She has a pair of black, oval-shaped glasses At the beginning of the movie, her hair is pulled back into a braid. She wears a pink patterned shirt under a purple long sleeved shirt that is finally covered by a white, hooded sweater. She wears denim jeans with a pink belt, and white trainers.
At the end of the movie, she only has on her pink shirt. Her hair is down as well and she seems to have a woven friendship bracelet on her wrist.
Marissa seems to be a shy and average girl. She's too nervous to tell her dad that she's too cold in her current seat in the classroom. She is imaginative enough to make her own characters after hearing about Sharkboy and Lavagirl for the first time.
When Max told her that she could defeat Mr. Electric with the Crystal Heart, she only hesitated for a moment before going ahead to face him in battle. She didn't falter at all when using her newfound ice powers against him.
Not much of her past is talked about. it's implied that her father, Mr. Electricidad, doesn't listen to her and tends to be more protective of her than he needs to be. Marissa is shown to have a mutual crush on Max and believed his stories about Sharkboy and Lavagirl from the beginning. She even drew her own dreamt-up superheroes: Ice Girl (herself), who gets powers from her Crystal Heart, and Dream Boy (Max).
Powers and abilities
The Crystal Heart gives her various ice abilities, not to mention the (hypothesized) ability to freeze time.
Mr. Electricidad is Marissa's protective father. While he cares for her, he seems to be a bit overbearing and protective. He even gets angry at Max for talking to her (assuming that he's flirting) as she's in his class. She doesn't seem to have any harsh feelings towards him.
Marissa is shown to have a mutual crush on Max. She believed in his stories from the beginning and encouraged them under her father's criticism. She had faith in him when he implied that she could defeat Mr. Electric.