Piplup was playing with his friends Pikachu, Charmander, and Chikorita one day when they ran into a Mew. Mew led them to a hole in the ground, which they all fell into. He then found himself in the PokéPark's Beach Zone. He later met a Wynaut who had gotten stuck on an island after some Sharpedo and Carvanha broke the bridge leading to the mainland from the island. Piplup swam to the island and kept the Wynaut company until Pikachu arrived with Bidoof who then proceeded to construct a new bridge so that Wynaut could get off the island. After Pikachu finds a hot air balloon, Piplup takes it back to the Meeting Place for repairs, and then journeys to the Iceberg Zone with Pikachu to confront Empoleon. Once Empoleon's been reasoned with, Piplup returns to the Meeting Place.
Piplup spends the remainder of his time at the Meeting Place repairing the hot air balloon. Once the balloon is repaired, he uses it to help Pikachu reach the Sky Pavilion once Shaymin is capable of guiding the way. At the Sky Pavilion, Piplup helps Pikachu look for Mew. Suddenly a second Piplup appears, and it's revealed to be Mew Transformed into Piplup to trick Pikachu. At the end of the game, Piplup is seen celebrating with all the other Pokémon.
PokéPark 2: Wonders Beyond
Piplup recently found a new PokéPark and invited Pikachu along to explore. When showing Pikachu the way, the pair meet a Timburr who challenges Pikachu to a battle. Once Timburr's defeated, the pair continue on to the Cove Area where they overhear a Krokorok and Sandile talking about a place called Wish Park. Piplup becomes fascinated by the sound of Wish Park and suggests that he and Pikachu check it out. On their way to Wish Park, they run into an Oshawott that thinks Pikachu is suspicious. However, Piplup vouches for Pikachu and introduces him as his friend, proving to Oshawott that he can be trusted. Piplup and Pikachu then find Krokorok and Sandile standing in front of a Portal Poster and pay the admission fee for Wish Park. They take part in Cofagrigus's attraction, Cake Contraption. Just as they were about to eat the cake they had made, a Pansear warns them of the effect it had on his friend, Panpour. Cofagrigus assures them that the cake is safe, and just as he was about to force feed them, Oshawott appears and knocks Cofagrigus aside. The trio then flee the scene as a pair of ominous hands appear and try to grab them. Just as they reach the portal to escape, one of the hands blocks their path. Piplup then shoves Pikachu and Oshawott through the spaces between the fingers and waves good bye as he is left in Wish Park.
Piplup remains in Wish Park warning other Pokémon of the dangers of Wish Park when he's found by a Zorua and Zoroark. They take Piplup to Pikachu, whom he announces his choice to stay in Wish Park so that he might help others. When Pikachu and the others return to Wish Park to rescue Victini, Gothitelle captures Piplup before letting Pikachu leave with Victini. Piplup is held captive in the Wish Palace until Pikachu arrives to deal with Darkrai. In a delusion, Piplup tries to coax Pikachu into staying in Wish Park so that they might play there forever. Pikachu refuses to stay, and the two do battle. The rejection leaves Piplup heartbroken who runs out of the palace crying. Pikachu is then put into a nightmare by Darkrai after he had erased Snivy, Tepig, and Oshawott's memories. Piplup soon finds Pikachu inside his nightmare and tells him that true friends never forget each other, and encourages Pikachu to seek out Snivy, Tepig, and Oshawott so that they may have a chance at defeating Darkrai. He then states that he has something he has to do himself and leaves.
Piplup returns with Reuniclus after Pikachu has battled against Darkrai. He states that he told Reuniclus what had happened, and Reuniclus invented a device that could close the Dark Void devouring the two worlds. Piplup is sucked into the Void along with the other Pokémon before Darkrai flies into the center of the void with Reuniclus's device, closing it and saving both the worlds, and all the Pokémon.