Pokemon the Series: Ruby & Sapphire Season 601 Episode 11 A Bite to Remember

On their way to Rustboro City, Ash and friends find themselves in a Pokemon preserve tended by a girl named Katrina, who takes care of the wild Pokemon and nurses them back to health. Max becomes attached to a Poochyena who hasn't yet evolved into a Mightyena like the rest of its group. Though Poochyena doesn't seem ready to evolve yet, and Ash and Brock try to explain that there's more to Pokemon than Evolution, Max becomes obsessed with the idea and takes Poochyena into the forest for training. When Team Rocket swoops in and attempts to nab everyone's Pokemon, Max and Poochyena must work together to defeat them--and the experience lets Poochyena evolve into Mightyena at last!