"Oh my gosh, how do I suddenly know which boy bands rock out loud?"
Cosma is the alternate, female ego version of Cosmo who Timantha wished Cosmo into, for reasons unclear, as it would be enough payback if she simply wished Wanda into Wando. Of course, Cosmo did say Timmy needed to be a girl for him to think of the perfect gift for Trixie.
Cosma is the result of Cosmo because Cosmo and Wanda were making fun of Timmy when Wanda turned him into Timantha. This angered Timantha and she made a wish where Wanda and Cosmo change their gender.
Her hair is a different shape than Cosmo, she has bangs parted in the middle, with a similar shape Mrs. Turner hairstyles. She wears a white band with orange flower, white with yellow earrings, lipstick pink, yellow necklaces, long eyelashes, and green shirt with dark green polka dots. Her voice is more high-pitched than Cosmo and cares a lot about her appearance like other women in the series.
Timmy in his room goes through his things, looking for a gift while Cosmo and Wanda watch. Cosmo suggests that Timmy could only think of the perfect gift for a girl is if he wished he was a girl. Timmy laughs saying it would be a waste of a wish and insults girls which angers Wanda so much that she turns Timmy into a girl. Cosmo clenches his teeth. Cosmo quickly says, "Who cares what you think? You're a girl now!" laughing very hard and causing Wanda to smile. Meanwhile, Timmy wishes that Wanda and Cosmo would switch genders and become "Cosma and Wando" to get back at them for wishing him into a girl. While he sits watching television and eating a hot dog, Cosma obsesses over what to wear. Wando tells her to just pick something. Cosma goes into the bathroom, only for a splash and her yelling, "Would it kill you to leave the lid down?" Wando only gives a snarly comment in return. She then drinks some soda before burping.
Outside the mansion, Timmy is satisfied that Trixie remembers his name, and realized it happened because he saw Trixie as a guy rather than a girl. He wishes Cosma and Wando back to the way they were born, and they revert to normal...with Cosmo getting a long, ugly nose that he says he was born with.
This is the first time Cosmo became a girl in the series.