This is one of the Pokémon you get from Professor Rowan in Pokémon Diamond and Pearl. It’s quite charming, so I’m sure there were quite a few people who chose it.
It emerges from the Poké Ball!
Suddenly, it starts sliding around using Surf!
The simpler the stage, the greater the effect of this may be. If you’re wondering why, it’s because anyone who gets caught up in that surf will get washed way with Piplup.
They’re getting washed away!
If you get washed away, do what you can to get back. Even simple characters like this really stir things up on stages.