Chimler first appeared in Stagestruck Starly, as one of the three Pokémon given to Platinum from Professor Rowan. Platinum sends him out of his Poké Ball alongside Turtwig and gives him a Pokédex for her bodyguards (who will arrive wearing red and green mufflers), and instructs him to give it to whichever one he likes. Matching the description, Chimchar chooses Pearl as his Trainer and gives him the Pokédex. Right after that, a flock of Starly appear and begin attacking the group, which results in the three starters fighting and defeating them.
In Ring Around the Roserade I, after leaving the Old Chateau the group meets Gardenia, who somewhat nudges them into challenging her the next day. The three soon begin training with the starter Pokémon when Cynthia walks by and notices that the three are going to evolve. Quickly after saying this the three evolve, with Chimler evolving into a Monferno.
As a Monferno
In Magnificent Meditite & Really Riolu I, Pearl buys a Zoom Lens with Coins Platinum won at the Veilstone Game Corner and suggests that Chimler try using the item since he has such bad aim. Aiming at a tree he fires Ember and nearly hits the local Gym Leader, Maylene. After a misunderstanding, Maylene assumes Chimler belongs to Platinum and wants to see him in their upcoming Gym battle. The next day Chimler battled against Maylene's Riolu. The two exchange a few attacks and Riolu gets the upper hand with its speed and lands a Force Palm. Riolu follows up by jumping onto Chimler, who blocks it. Although blocked, Riolu begins to use Drain Punch to steal his energy, forcing Platinum to switch him in. He is later sent back out to fight Riolu and it uses Rock Smash to scatter the field with rocks in order to hide Riolu. Platimun and Chimler manage to hit and knock out Riolu thanks to the Zoom Lens and Platinum's training at the Game Corner.
In Stunning Staravia & Stinky Skuntank II, Chimler fought against some Galactic Grunts in order to stop them from capturing Platinum. He starts by using Ember to attack a Skuntank, impressing Paka and Uji. With their advice Tru uses Stealth Rock to assist Chimler by making a platform for him to reach the middle of the battle. Chimler uses a spinning Ember, defeating the group of Staravia. The two then evolve into Infernape and Torterra and the group flees to the top of a building with a satellite dish on top of it. With Paka and Uji's guidance Chimler attacks wildly with Ember and Tru attacks with Earthquake, causing the satellite dish to fall on top of the Grunts. Pearl then realizes that Chimler's random attacks forced the Grunts into the spot behind the satellite and weakened it at the same time. With Tru's Earthquake knocking it down the Grunts had nowhere to run, trapping them.
In Outwitting Octillery, Chimler works alongside his team to reach the middle of Lake Valor in an attempt to find Azelf. Halfway across the lake they get attacked by Saturn's Octillery, who uses Octazooka to destroy their raft. Saturn shows up on a UFO-like vessel and grabs Pearl while demanding to know why he was heading for the island at the middle of the lake while Chimler, Chatler, and Rayler desperately try to free him. A few minutes later the Galatic Bomb goes off, with its target revealed to be Lake Valor. Pearl and Saturn witness Azelf reveal itself and Saturn and his grunts begin trying to capture it. Pearl and his team attempt to stop them but are overwhelmed by the number of opponents and defeated.
Chimler, as a Chimchar, appeared to be very lazy. He could usually be seen resting on a chair or bed and dangling off of his Trainer's arm at times. He is a mischievous Pokémon and loves to play around, though he always listens to Pearl. When not used in battle, Chimler would make great use of his Ember technique which could be used to melt glass or metal so they can get into various places. Chimler also seems to be very ticklish, especially when he comes in contact with grass. In battle, he is a very strong Pokémon and is the powerhouse of Pearl's team.