A Gible was abandoned in the streets by an abusive Trainer, who left her behind. She was later found and brought to Professor Sycamore by Alain. Gible did not trust Sycamore at first, even biting his hand. Sycamore did not mind, since he wanted to befriend Gible and, as time went by, she started bonding with him.
Some time later, Gible evolved into a Gabite.
She was later introduced to Ash and his Pikachu after they took a Froakie who previously saved Pikachu from Team Rocket to the Pokémon Center. When Team Rocket attempted to capture Froakie, Garchomp defended it from Team Rocket's device which then attached itself to her. This caused her a lot of pain and she went on a rampage across Lumiose City, rapidly using Hyper Beam. Luckily, Ash managed to calm down Garchomp and break to brace off her neck while they were on the Prism Tower. She, along with Froakie, watched in terror as Ash dove down to save Pikachu, but was miraculously saved by a Mega Blaziken at last minute. Once the crisis was over, Garchomp returned by to normal and happily reunited with Sycamore.
She met up with Ash and his friends again to help demonstrate the power of Mega Evolution with Mega Stones. The demonstration was interrupted when Team Rocket showed up, stole to Mega Stone machine, and abducted Garchomp. While Sycamore was trying to find Garchomp, he thought of how he first met her and how Garchomp befriended him. Team Rocket tried to get Garchomp to Mega Evolve, even using the radio waves to subdue her, but Professor Sycamore and the heroes arrived at the scene with an unexpected appearance of a masked man called Blaziken Mask, who lent Sycamore the Key Stone. Once James and Sycamore pressed their Key Stones, Garchomp Mega Evolved. Mega Garchomp was furious, but Sycamore managed to get Garchomp to remember him. Mega Garchomp calmed down, then slashed Team Rocket's machine and sent them blasting off, with the help from Mega Blaziken and Pikachu. With Team Rocket gone, Garchomp returned to her trainer once again.
Since Mairin was in danger, Sycamore sent Garchomp to battle Team Flare grunt's Skorupi. Garchomp used Dragon Claw to counter Skorupi's Poison Sting. After the collision, Mairin, Sycamore and Garchomp retreated away from the grunt. Mega Garchomp was also used to stop Druddigon's Dark Pulse. Since Serena and Mairin planned on rescuing Chespie from Lysandre Labs, Sycamore called his Mega Garchomp back and joined the girls in the rescue mission.
Sycamore sent his Garchomp to battle the Giant Rock, alongside Serena's Braixen and Steven's Metagross. Sycamore and Steven Mega Evolved their Pokémon; Mega Garchomp used Dragon Pulse on the Giant Rock, which blocked the attacks with the plants. As Mega Garchomp repeated her attack, the plants grasped and bound her and the other Pokémon. Fortunately, Ash's Pikachu used Iron Tail, which freed Mega Garchomp. Continuing the battle, Mega Garchomp fired Hyper Beam, but was once more bounded by the plants. The Gym Leaders arrived and had their Pokémon launch attacks at the Giant Rock, which freed the Pokémon. Sycamore and Mega Garchomp joined the fight to thwart away the sprouted plants. Mega Garchomp used Dragon Rage to stop the plants before Sycamore was pulled away by the plants, along with Malva. Once Chespie was rescued, Mega Garchomp launched an attack at the Giant Rock, which fused with others' attacks to destroy it. Along with its trainer, Garchomp watched as Squishy and Z-2 destroyed the Giant Rock and defeated Lysandre.
Once the order was restored, Alain visited the professor's Pokémon inside the lab, including Garchomp.
Ash remembered Professor Sycamore and his Garchomp fighting the Giant Rock with the rest when he was reflecting back on his journey.