Zee meets a shy girl named Casey Krinsky, who is immediately befriended by her. At lunch time, Zee introduces her friends to Casey, who brought the tots for them to eat and they all became friends. However, on the following days, Zee is getting creeped out by Casey who is obsessed with her and used her belongings to get her on schedule to meet with her. As she went to the restroom, Zee has had enough with Casey following her every day, which hurts Casey's feelings.
Zee feels guilty of what she has done and she apologized to her, but suddenly, Casey reveals herself as a supervillain made of crystals and, not only did she steal her looks and her superpowers, but she switched bodies with Zee's magic. Casey in Zee's body tells the girls that she is Zee and that "Casey" is talking crazy, which they immediately ditched Zee in Casey's body.
Later, at Sweet Justice, Babs opened the door to the secret base, in which Casey finds out that the girls are the Super Hero Girls and steals their looks and superpowers, turning her into a giant fusion of the Superhero Girls. With the girls unable to stop her without their superpowers, Casey spots Zee and chases after her to the amusement park. But then, Zee enters the hall of mirrors and outsmarts Casey as she breaks the mirrors, forcing her to use her magic to give all of the superpowers back to the girls and switched her body back. Casey was horribly mad at her as she runs off to tell everyone the girls' secret identities, but fortunately, nobody believed her.
In mainstream DC Comics, Casey Krinsky is a somewhat obscure character first appearing in Firestorm vol 3 #4 as an adversary of the second Firestorm, Jason Rusch. To which she developed a psychotic infatuation for.
In this episode, Casey knows the secret identities of the Super Hero Girls.
This episode reunites Lara Jill Miller, Grey Griffin and Tara Strong, who voiced Widget, Wubbzy, and Daizy respectively from the Nick Jr. series Wow! Wow! Wubbzy! In additon, the three have voiced various characters in other Nickelodeon properties, such as The Loud House and The Fairly OddParents.
Diana was near a kitten that Casey gave to her and the others, yet in "Rage Cat," she was shown to be allergic to Dexter when Jessica tried to find him a home.