Jimmy obtained Cyndaquil from Professor Elm on the same day that Vincent got his Chikorita and Marina got her Totodile.
Cyndaquil would soon become one of his closest Pokémon. At the very beginning of his journey, Jimmy used Cyndaquil to battle Silver, but he was defeated by the power of his rival's Nidoking.
The defeat made them decide to become increasingly strong and Cyndaquil soon evolved into a Quilava and some time later into a Typhlosion. Thanks to his arduous training, the duo eventually managed to defeat Silver, which brought the two even closer.
Jimmy used Typhlosion to defeat Shinji and his powerful Hitmonlee. After a hard-fought battle, Typhlosion and Jimmy emerged victorious and then complimented Shinji and his Pokémon.
Later, Typhlosion was used in Jimmy's battle against Marina and Wani-Wani, where Typhlosion shrugged off Water Gun despite the type disadvantage. The battle was then interrupted because of Team Rocket's mission to capture Raikou.
Jimmy then used Typhlosion to battle Attila's Skarmory and Hun's Steelix, but it was defeated by Ground-type attacks and Steelix and Skarmory's combined attacks. In order to protect Jimmy, Typhlosion tried to battle the wounded Raikou, but Jimmy stopped it. After retrieving its energy, Typhlosion was used again to save Raikou from the clutches of Team Rocket, and Typhlosion used its Fire attack, alongside the attacks of Meganium and Little Miss, to try and destroy Team Rocket's machine.
Jimmy used Typhlosion once again in order to save Raikou from the machine, and it used all of its strength to save the Legendary Pokémon alongside Meganium. Typhlosion was later seen with Jimmy, his friends, and their Pokémon as they said goodbye to Raikou while the Legendary Pokémon went on its own way.
In Pride of a Champion!, Typhlosion appeared watching the Masters Eight Tournament match between Lance and Diantha on TV.
Like Ash and his Pikachu, Jimmy and Typhlosion are very close to each other. In The Legend of Thunder!, it was seen out of its Poké Ball most of the time. Like Jimmy, one of Typhlosion's defining traits is its immense willpower, and it doesn't like to give up, even in the face of danger.
As a friend, Typhlosion likes to battle for fun, and is aware of Jimmy's feelings for Marina. Nevertheless, it is extremely loyal to Jimmy, to the point of confronting the power of a Legendary Pokémon even though seriously wounded after a battle.