Garchomp was Cynthia's most powerful Pokemon. She debuted in Top-Down Training, where she battled Lucian's Bronzong and won, blocking Flash Cannon with one of her fins and then defeating Bronzong with an incredibly powerful Giga Impact, which normally would not do much damage to a Steel type.
She also battled against Paul in the same episode, knocking out Chimchar, Weavile, Murkrow, and even Pauls most powerful Pokemon Torterra. She defeated each of them with just one attack and endured Weavile's super effective Blizzard with astonishing ease. Garchomp showed the ability to block Flash Cannon and even Frenzy Plant by using her fins as a shield.
Garchomp later appeared when Cynthia was challenged by Aaron battling his Drapion. Whether she won or lost this battle is unknown.
Garchomp also helped battle Team Galactic on two occasions, first when attempting to stop them from stealing the Lustrous Orb and later when preventing them from taking over the Pokemon universe by using the powers of Dialga and Palkia.
Garchomp also battled Flint's Infernape when Flint challenged Cynthia for the title of Sinnoh League Champion. Infernape dodged Garchomp's Draco Meteor and attacked with Close Combat. Garchomp smashed Infernape to the ground with Brick Break and then Infernape struck back with Mach Punch before using another Close Combat. Garchomp retaliated with Stone Edge and then intercepted Infernape's Flare Blitz with Dragon Rush creating a huge explosion. When the smoke cleared, Infernape collapsed and Cynthia was announced the winner.
Garchomp also appeared when Cynthia traveled to Unova where she battled Iris' Axew, taking Axew's Scratch and blocking Dragon Rage before almost knocking Axew out with Dragon Rush and Draco Meteor. Axew learned Giga Impact during the battle and actually managed to knock Garchomp off her feet which was quite remarkable especially when one considers the fact that Axew was only in its first stage of evolution. However Garchomp quickly recovered and would have defeated Axew with Brick Break if Cynthia hadn't called her off at the last moment.
+ indicates this Pokémon used this move recently.* - indicates this Pokémon normally can't use this move.
Cynthia's Garchomp has never been seen losing a battle and is easily one of the most resilient and powerful Pokemon in the anime, rivalling most, if not all Legendary Pokemon. However when Cynthia battled Aaron, her final Pokémon was Gastrodon, implying that Garchomp was defeated in this battle.
Interestingly when Garchomp battled Iris' Axew, her Brick Break was used with only her claw whereas in all of her previous uses of the move she used her entire fin. This makes Brick Break look more like Dragon Claw. It is possible that she wasn't using Brick Break at full power, since Axew had already taken severe damage which may have been why only her small (albeit sharp) claw was glowing rather than her massive fin.
For some reason when Garchomp battled Flint's Infernape they appeared on opposite sides of the battlefield from their trainers when Dragon Rush and Flare Blitz collided, suggesting that Garchomp and Infernape had not actually hit each other directly but instead the explosion was caused by friction as they passed each other. Another possibility is that considering Infernape's athletic abilties, it might have somersaulted over Garchomp just before the explosion which could explain why Infernape was still standing for a few seconds after the explosion despite the recoil damage from Flare Blitz and all the previous damage it had taken, since it didn't have to take the full power of the blast. Either way, Garchomp won the battle.
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