Piplup initially would not accept food from Dawn—as described in the Pokédex, Piplup are very proud and dislike accepting food from people. However, it seems to have a large appetite for Pokémon food and does not like having any taken away from it. It shows signs of having a short temper, frequently getting into disagreements with other Pokémon and its Trainer.
Piplup is Dawn's main battling partner, used more than any of Dawn's other Pokémon and has helped Dawn win her first two ribbons in Sinnoh. Piplup seems to be very competitive; it will always try to overcome the odds and impress Dawn and get her fullest attention. It often wants to be the first one to start an event for Dawn, and also often tries to peacefully talk to enemies, rather than just attacking them, as seen for example in The Psyduck Stops Here!.
It has been shown that Dawn and Piplup have a close bond with each other. In Staging a Heroes' Welcome!, Piplup helped Dawn recover her confidence by shooting BubbleBeam at her face.
In A Breed Stampede!, it was shown to be quite adamant and overconfident. It even tried to stop Piloswine from charging. However, each attempt resulted in being launched into the sky and knocked out. It tried again when Piloswine had already evolved into Mamoswine, but the result was again the same.
In Stopped in the Name of Love, Piplup began the evolution process. However, it soon became clear that Piplup was unwilling to undergo the transformation to Prinplup. After an encounter with Team Rocket, Dawn gave Piplup her full support and acquired an Everstone to prevent its evolution.
In Team Shocker!, Piplup, Pachirisu and Buneary are cheering for Dawn in cheerleader outfits. This may suggest Pachirisu, Piplup, and Buneary are female. It is also seen in a cheerleader's outfit again in A Triple Fighting Chance cheering for Ash. However, in Tanks for the Memories!, when Dawn and Ash's Pokémon are dressed as maids, Piplup, along with Ash's Turtwig and Pikachu, were all blushing in embarrassment. This could be hinting that it may be male instead.
In The Psyduck Stops Here!, Dawn tried to understand what Piplup was telling her, saying 「僕にまかせろって？」 Boku ni makasero tte? meaning Are you trying to say "Leave it to me"?. Dawn uses the Japanese pronoun 僕 Boku (meaning I, mostly used by males) for Piplup. This may mean Piplup is male. Within the games as well, Piplup have a 7/8 chance of being male. However, Anabel also uses the pronoun to refer to herself, because while Boku can be used for males and usually is, it is not unheard of for females to use it.
The opening sequence of Pokémon shows Dawn's Piplup coming out of its Poké Ball with a trail of stars behind it. However, Dawn has never used a star seal with Piplup's Poké Ball.
Dawn has been keeping Piplup outside of its ball, instead of inside of it, much like Ash keeps his Pikachu, though Piplup never expressed distinctly that it did not like being inside of the ball.
In addition, Piplup wasn't ready to obey Dawn when they first met. Eventually, they became fast friends after Pikachu and Piplup saved their respective trainers from an attacking group of Pokémon; Pikachu saved Ash from a flock of Spearow while Piplup saved Dawn from a swarm of Ariados.
Also, it has expressed reluctance to evolve and chose to stay in its base form for the time being, and Dawn was given an Everstone to prevent Piplup from evolving.
Piplup is Dawn's only Pokémon whose species is not based on a real-world mammal.
During an interview with former director and storyboard artist of the Pokémon anime, Masamitsu Hidaka, he revealed that Dawn's Piplup will probably not evolve very soon, referring to its evolutions as "ugly" or not good for contests.
Of the current number of Diamond & Pearl series episodes, Piplup has only been completely absent from 17.
Piplup is the second Pokémon in the anime to stop evolving while the process is happening, the first being Ash's Bulbasaur.
. The following is a list of cards named Piplup 
