In The Manga
In the manga Pokémon Adventures during the arc based on Pokémon Ruby and Sapphire, Ruby, the male protagonist, obtains a Mudkip named Zuzu as his starter Pokémon from Professor Birch. Ruby becomes a Pokémon coordinator, a person who uses their Pokémon for contests rather than battles, and uses Zuzu in those contests. At the beginning Ruby was disappointed with it because it wasn't pretty enough like his other Pokémon, but then he decided that Tough Contests would be perfect for it. Zuzu was first used to battle against Sapphire, Ruby's rival in the manga. Zuzu evolved into a Marshtomp unexpectedly while Ruby was in Slateport City, and again into a Swampert, while training near Fortree City.
A Mudkip also made a minor appearance in Pocket Monsters Chamo-Chamo ★ Pretty ♪, a sequel to Magical Pokémon Journey.
Read more about this topic: Mudkipz, Appearances