Dexter's Laboratory - Season 1 - Eps 7: Dexter's Rival
Mandark Astronomanov, a new student at Dexter's school, seems to be superior to Dexter academically. Mandark forces Dexter to shut down his lab so that Mandark's lab can gain more power. However, with the help of Dee Dee, Dexter manages to destroy Mandark's lab.
About Dexter's Laboratory

Title: Dexter's Laboratory
First Air Date: 1996-04-28
Last Air Date: 2003-11-20
Status: Ended
Rating: 7.7/10 (from 813 votes)
Language: EN
Seasons: 5
Total Episodes: 220
Network: Cartoon Network
Genres: Animation, Comedy, Sci-Fi & Fantasy
Production Companies: Hanna-Barbera Productions, Cartoon Network Studios
Synopsis
Dexter, a boy-genius with a secret laboratory, constantly battles his sister Dee Dee, who always gains access despite his best efforts to keep her out, as well as his arch-rival and neighbor, Mandark.
Cast

Candi Milo
Dexter (voice)

Kat Cressida
Dee Dee (voice)

Jeff Bennett
Dad (voice)

Kath Soucie
Mom (voice)

Eddie Deezen
Mandark (voice)