Pokémon Ultimate Journeys

On their travels, Ash, Misty and Brock, meets a trainer that take them to the Charizific Valley, a place where wild Charizards battle each other to become stronger. Ash's Charizard realize that he isn't so unbeatable as he once though and want to stay and become stronger, but the wild Charizards refuse to take him in before he can prove his strength.