Charmander made its proper debut in Summer of Discovery!, where it ran downstairs and greeted Ash and his friends along with their Pokémon. Charmander had a First-Touch Battle with Clemont's Chespin. It won after accidentally catching Chespin's tail on fire.
In A Legendary Photo Op!, it was revealed to have evolved into a Charmeleon. Trevor sent it to battle Ash's Fletchinder. Despite putting up a fight, it was defeated by Fletchinder's Steel Wing. Later, at Mt. Molteau, Trevor used Charmeleon in a Tag Battle alongside Ash's Fletchinder against James's Inkay and Jessie's Gourgeist. Their battle disturbed a Moltres slumbering in the volcano and the battle was interrupted. Charmeleon attempted to battle Moltres to calm it down but it was unsuccessful.
It reappeared in A League of His Own!, where it was revealed to have evolved into a Charizard. It was used to battle Alain's Charizard in the first round of the Lumiose Conference. Trevor's Charizard opened with Fire Spin, which Alain's Charizard dodged by flying in the sky. Alain's Charizard then retaliated with Flamethrower, with Trevor's Charizard blocking the attack with Dragon Claw. Trevor then revealed his Key Stone and Mega Evolved his Charizard into Mega Charizard Y. Upon Mega Evolving, Mega Charizard Y's DroughtAbility activated, creating harsh sunlight and powering up all of its Fire-type moves. Trevor's Mega Charizard Y then attacked with Heat Wave, but Alain's Charizard was able to block it, creating a water shield by slamming its tail into the nearby stream. Trevor's Pokémon then flew up to attack with a Dragon Tail, but Alain's Charizard dodged the attack. Alain's Charizard then Mega Evolved as well and countered a Fire Spin with Flamethrower, creating a cloud of smoke. Trevor had his Charizard fly into the sky, but Alain's was able to spot it through the smoke and defeated it with a single hit from Flamethrower.
As a Charmander, Charizard was an energetic, if not hyperactive, Pokémon, who loved to battle. It was often seen running around when not in battle.
Similar to Ash's Charmeleon, Trevor's Charmeleon was very aggressive to the point that it attacked its own Trainer at one point and even other Pokémon. However, during battles it gladly accepted Trevor's commands and was also shown to have retained traits it had when it was a Charmander, such as its love for battling others to test its strength.