Pelipper

As you might expect of such a ubiquitous Pokemon in-game, Pelipper is not particularly amazing. However, while many of such common Pokemon are usually extremely lackluster, Pelipper is surprisingly decent. His rare typing gives him access to a fantastic STAB combination that's only resisted by Lanturn in UU and a slew of interesting resistances that allow him to check a few common Pokemon in the UU metagame. Additionally, his stats, while not top-notch, are not really poor; a great Defense stat and passable Special Attack give him the ability to be a decent tank. He also has access to all the right moves that allow him to perform his role well. All in all, while Pelipper may seem like another mediocre Water-type that's outclassed by bulkier alternatives such as Milotic, Pelipper has more than enough unique traits to distinguish himself from them and is still somewhat competitively viable.