Empoleon, as a Piplup, was given to Platinum by Professor Rowan along with two other Pokémon. When Platinum started her journey, she chose Piplup as her starter Pokémon and let her out of her Poké Ball.
Later, at Oreburgh City, Platinum was attacked by a group of wild Kricketot and Kricketune, forcing Piplup to defend her. Despite her best efforts, Piplup is unable to defeat them entirely, which deals a huge blow to her pride. In an attempt to regain her self-respect, Piplup trains with Chimler and Tru to prepare for Platinum's upcoming Gym battle against Roark.
The next day, Piplup faces off against Roark's Cranidos at the Oreburgh Gym, but is hurt by a powerful Shock Wave and it forced to be sent back. After Ponyta falls to Roark's Onix, Piplup is sent back out and quickly defeats it with a Water-type attack. With some advice from Diamond and Pearl's comedy routine, Platinum commands Piplup to use Water Pulse, which confuses Cranidos and causes it to knock itself out, giving Platinum the victory and Piplup regains her pride.
Later, in another training session for Platinum's next Gym battle, Piplup, along with Chimler and Tru, evolve into their next stages. Later, Prinplup, along with Ponyta, faces Gardenia in Platinum's Gym battle. After Ponyta is quickly defeated, Prinplup faces Gardenia's Pokémon alone and manages to beat them with a super effective Blizzard, giving Platinum her second win.
After the group arrives in Hearthome City, Platinum and Prinplup get involved and enter in a Pokémon Contest. Due to several saboteurs working against them, Platinum and Prinplup lose their confidence and consider quitting. However, with words of encouragement from Diamond, they gain enough confidence to continue going on and manage to win the contest.
Later, Prinplup helps Platinum train for her upcoming Gym battle against Maylene and acts as her Riolu since she wasn't being used in the battle. Prinplup later evolves into an Empoleon offscreen after Platinum is knocked unconscious and put into the Veilstone Department Store by Paka and Uji.
Empoleon is used in Platinum's next Gym battle against Crasher Wake. She is used against Wake's Floatzel and the two begin exchanging blows before taking the battle to the waters. Empoleon manages to easily beat Floatzel with a Vacuum Wave but is defeated by Wake's Quagsire after losing to a Blizzard. Later, when Platinum faces Fantina in a Gym battle, Empoleon is used against her Drifblim and wins by freezing its Ominous Wind with Blizzard but loses to her Mismagius soon after.
When Platinum goes to find her kidnapped father, she uses Empoleon against the Gym Leader Byron, who she believed to be the perpetrator. Empoleon manages to damage Byron's two Bronzong but is defeated by a Payback attack. Empoleon is also used in the Gym battle against Candice, where she easily defeats her Snover but ties after being defeated by a Seed Bomb.
As a Prinplup after winning a Contest
When Platinum was trying to convince Volkner to train her, Candice, and Maylene, Empoleon was used against his Raichu. Even though she managed to trap it in ice with Blizzard, Raichu managed to free itself with a Berry and defeated Empoleon with Thunderbolt. After Volkner accepts, Empoleon was used to battle his Electivire and manages to win, earning Platinum her final Badge.
In the Platinum chapter, Empoleon is first used for Platinum's challenge in the Battle Castle. Empoleon faces off against Darach's Gallade but is nearly defeated and switched out for Rapidash. Later, she faces off Darach's Houndoom and Staraptor and defeats them with ease before being switched out with Lopunny. Once Lopunny is defeated, Empoleon finishes off the Attract-inflicted Gallade with Drill Peck, giving Platinum her first Battle Frontier win.
Platinum uses Empoleon in her Battle Arcade challenge in her battle against Arcade Star Dahlia. During the battle, Platinum and Dahlia switch Pokémon, which meant Empoleon and Platinum's other Pokémon are forced to fight their Trainer. Although both sides are reluctant at first, both Platinum and her Pokémon fight at their full strength, which eventually ends with Platinum as the victor.
When Platinum goes to challenge the Battle Factory, she sends Empoleon and her other Pokémon to go search for Looker on Stark Mountain, who had gone missing previously. They soon return, heavily injured and exhausted with a similarly injured Looker and Buck.