James's loyal Growlithe has helped save James from Jessiebelle on countless occasions. When James left his home, Growlie stayed at home in its own mansion.
James later re-encounted Growlie at one of the mansions in the Sinnoh region. It was able to smell James under his disguise.
Growlie despises Jessiebelle as much as James does. It was shown in one of James's memory flashbacks that Jessiebelle ordered him to replace Growlie, James's beloved partner, with a Skitty, and that made him so upset that he left her house yelling he doesn't want to marry her. On his way back home, in his effort to dispose of the treasure chest so she wouldn't find out about the love letter he wrote, James told Growlie to use Dig and hid it in the forest.
After Jessiebelle arrived at the mansion due to being contacted by Sebastian, it joined James when he tried to escape from her and his butler. When at a safe distance from them, James tried to open the chest in order to dispose of the letter it contained. However, he guessed the password three times wrong, and thus the treasure chest transformed into a mecha once again. The mecha then fired a laser beam at James, but Growlie prevented it from hitting its master by using its powerful Flamethrower. James then joined the puppy Pokémon's effort to take down the mecha. Even though one of the missiles hit it, Growlie didn't retreat, and with renewed strength, it managed to take it down using its Flamethrower and Dig attacks. The chest then transformed into a rocket, and flew off into the sky.
Seeing as there was no other way to escape from Jessiebelle and his mischievous butler, James asked Ash to have his Pikachu use Thunderbolt on him, Jessie and Meowth. Ash agreed, and during the blast-off, James bid farewell to his loyal Pokémon.