Piplup when it was introduced from the beginning as being serious and arrogant but is also a little bratty. His arrogance causes him to become defenseless or being fainted in battle. Piplup is best friends with Ash's Pikachu seeing him as a companion while traveling with their Pokémon Trainers like Ash and Brock are to Dawn. Also, Piplup is best friends with Ash's Torterra and Infernape. Like Bulbasaur, Squirtle, Pikachu and Snivy, Piplup wants to prove he can become stronger without evolving.
In Memories Made Of A Bliss! which is the finale of Diamond and Pearl series, Piplup was deeply emotional and does not want to be parted ways with its best friend Pikachu which it angrily runs away and cries not to come back but Pikachu reassures they will be back soon making the two emotionally cry together. Piplup gains his confidence back after teaming up with Pikachu to stop Team Rocket in their final battle.
When Dawn reunites with Ash with his new friends, Iris and Cilan in the Unova region, Piplup has a strong rivalry with Ash's Oshawott due to both are Water-type Starter Pokémon are competing and fighting each other because both had a huge crush on the Mythical Pokémon, Meloetta upon her introduction. However, Piplup and Oshawott ended their rivalry and became good friends after they had to say goodbye.
Piplup first meet Dawn when she saved him from a group of Ariados as she left Professor Rowan lab to look for him. Although he was grateful for the rescue, Piplup wasn't interested in Dawn. However, Piplup changed his opinion about Dawn when she attempted to hold the Ariados off while he made his escape but he chose to protect her instead of running away. After that, Piplup and Dawn became best friends as she even chose him to be her starter Pokémon which began their partnership. Piplup would do anything to protect Dawn and she would do the same for him. Despite their friendship, Piplup and Dawn do butt heads from time to time but don't stay mad for long. At times, they run a lot of obstacle together that almost ruined their friendship but they make amends in the end and it ended up making their bond for each other stronger. Piplup would usually be held in Dawn's arms but he has sit on her shoulder or head.
Piplup has a caring relationship with his teammates and their also his closest friends but does sometimes butt heads with them. Despite this, Piplup would choose their safety and would try his hardest to protect them no matter what. In contest, Piplup has shown to work well with some of his teammates whenever it was a double performance.
Piplup was the first Pokémon Dawn ever had. They met in the first Diamond and Pearl episode, Following a Maiden's Voyage!, when the starter Pokémon from Professor Rowan's lab, Piplup and a starter Chimchar, ran off. Dawn decided to try and find them, and Piplup was the first one she found. By the time the rest of the Pokémon were recovered, Dawn had grown attached to Piplup, and decided that it would be her Starter Pokémon.
Dawn's Piplup can be stubborn at times and it's also very proud like Piplup are. Overall, though, it is loyal to Dawn and has helped her and her friends many times both in and out of battle (but always got lost when leading). Piplup has been shown that he deeply cares about Dawn, such as in the episode Stopped in the Name of Love! where Piplup's time for evolution has finally come. However, Piplup refused to evolve and has reasons for not wanting to. Piplup first reason for not wanting to evolve is that he was afraid that if he would to evolve he would start disobeying Dawn just like his teammate Swinub did after it evolved into a Piloswine and when it evolved again into Mamoswine. Piplup second reason for not wanting to evolve is because he wants to prove he can become stronger without evolving as his best friend Pikachu was his main inspiration for this reason, after seeing how determined he was to prove he can be strong without evolving. Piplup main reason for not wanting to evolve is because the day he and Dawn meet was the day they chose each other to be their partners as he wanted to stay her Piplup forever. In order to stop his evolution, Piplup transferred the energy of evolution powering up his attack Bide. Dawn respected Piplup's choice as she got an Everstone from Nurse Joy and decided to keep him by her side. Piplup has also been shown to have developed some kind of rivalry with baby Cyndaquil regarding Dawn's attention.
In the episode Where No Togepi Has Gone Before!, Piplup is confirmed to be male along with Pikachu, Croagunk and Meowth due to the effect of Attract used by a very mischievous Togepi. Even though it is seen holding pom-poms during Ash's battle with Roark.
Piplup has recently become a target of Gible's Draco Meteor attacks as every Gible's Draco Meteor manages to hit Piplup no matter where he is. In the episode "Piplup, Up and Away!", Piplup is once again hit by the move but is even more saddened when he notices that Ash and Dawn are paying more attention to Gible than to him. Jealous, Piplup runs away only to bump into disguised Team Rocket who pretend to be the aids of Professor Rowan. Suddenly, a wild Rhyperior starts rampaging splitting everyone up. In the same episode in order to save Dawn, Piplup learns a powerful move, Hydro Pump and so manages to attack Rhyperior.
In Piplup, Pansage and a Meeting of the Times!, he returns along with Dawn in East Unova, and is identified by Ash's Pokédex to show Iris. Later in the episode, he falls in love with Meloetta and fights with Ash's Oshawott. He later battles Cilan's Pansage and wins, despite the type disadvantage and is revealed to have learned Ice Beam (likely to counteract the weakness to Grass-type moves and Grass-types in general, who are weak to Ice moves).
- Counter Shield
- Sweet Kiss Bubble Beam
- Discharged Whirlpool
- Water and Fire Whirlwind
- Dawn Plan A
- Aura Sphere Bubble Beam
- Aura Whirlpool
- Sky Attack Peck
- Hydro Volt Tackle
- Flaming Whirlpool
- Big Bubble
- Piplup is the only Sinnoh starter Pokémon to be owned by a main character other than Ash, as well as the only one to never evolve.
- Piplup almost did but kept fighting it off until receiving the Everstone.
- A running gag during Sinnoh after Ash caught Gible was that it would be on the business end of Gible's repeatedly misfiring Draco Meteor attacks.
- One only hit it because Barry's Empoleon, the intended target, deflected it away on Barry's command to "hit it back".