Paul's Ninjask was a Pokémon captured before Paul met Chimchar.
Ninjask was shown being captured in a flashback in Glory Blaze, only minutes before Paul captured Chimchar.
In A Real Rival Rouser, it was revealed Paul still had his Ninjask, and he chose it to fight Ash's Gliscor. Using its incredible speed, which was augmented by Agility and its special ability Speed Boost, Ninjask almost defeated Gliscor but Ash recalled the Fang Scorp Pokemon and replaced it with Infernape. Despite Ninjask's speed, Infernape managed to anticipate its movements and knock it out with Mach Punch