Dee Dee's Rival is the first part of the 35th episode in season 2 of Dexter's Laboratory, which first aired on April 15, 1998. In this episode, Dee Dee meets her rival, Lalavava, a new student in her dance class and Mandark's sister, who tries to upstage her.
Dee Dee wakes up and gets ready for the first day of her dance class. She goes through a wake up montage similar to the one Dexter did in the episode Dexter's Rival. She gets dressed and Mom drives her to her dance class, and her dance teacher Miss Babcock welcomes her back to the new year. Then, there is a noise heard and everyone directs their attention to a dark and scary figure in the shadows of the corner of the room. Mrs. Babcock says that this is their new student. She comes up and Mrs. Babcock says her name is Olga. Olga says that people can just address her as Lalavava.
Lalavava gets out on the dance floor and starts doing a dance that everyone seems to love. After Lalavava is done, she walks past Dee Dee and snaps her fingers in her face. Dee Dee wants to show that she is the real best dancer and she busts out and starts dancing. Lalavava gets mad at Dee Dee for trying to be better than her so she breaks out dancing and trying to be better than her. Dee Dee and Lalavava both start continuously dancing and trying to be better than the other. Finally, they both stop and are exhausted from trying to beat each other. Miss Babcock is equally impressed by the both of them and she says that she will make the play into a duet. Dee Dee and Lalavava are both shocked and unhappy with this. They decide that they will get help from their brothers for this.
Dexter is working in his laboratory on an invention. Then, he hears Dee Dee coming and he sighs, takes out a hammer and he smashes his invention before she gets there. Dee Dee politely says that she needs help with a problem she's having with another girl at her dance class. Lalavava comes home and goes to her brother Mandark, and she rudely tells him to “use his science junk to help her beat that skinny creep”. Dee Dee begs and pleads for Dexter to help her, and she acts so nice toward him, complimenting him and treating him good so that he will help her. Lalavava threatens to break Mandark's face if he doesn't help her. Mandark trembles in fear before Olga and Dexter decides that he will help Dee Dee with her problem. Dee Dee thanks Dexter by giving him a kiss and Lalavava "thanks" Mandark by flicking his nose and laughing.
Later at the ballet dance, the play is about to begin and Dexter, Mom, and Dad are sitting in the audience watching. When the play begins it starts off calm and peaceful with one little girl dancing, then when Dee Dee and Lalavava come up, they are in giant robot suits, which shocks the audience. Dee Dee and Lalavava both start dancing, which rumbles everything and breaks stuff apart. Dee Dee and Lalavava competitively dance and then, their dance breaks out into a fight. They both start punching and blasting missiles and firing lasers at each other, and soon they’ve both caused a lot of damage to the theater and the person in the play everyone loved the most was the girl at the beginning of it. Everyone cheers and throws flowers at her and Dee Dee and Lalavava are up there angry that they both lost. They find out that the other also has a nerdy brothers with a secret laboratory, and the girls agree that science stinks. They decide to put their differences aside and become friends, and they both break through the wall and walk off to the mall.