Poliwag, the Tadpole Pokémon. It has no arms, but its tail makes it a good swimmer.
– Ash’s Pokedex
Poliwag is based on a tadpole. Looking closely at its face, its mouth is kinda derpy-looking, haha. The swirls on its belly reverses direction when it evolves into Poliwhirl. Like Wooper, it has no arms until it evolves. Yet it can learn DoubleSlap, maybe it uses its tail I guess.
In the Dreamworld, Poliwag with Swift Swim is available in the Forest area if you have more than 10000 Dream points (which you get for playing a lot). I remember grinding the Dreamworld a lot for points in order to catch Poliwag, because it can evolve into Politoed with Drizzle.
Stat-wise, it has good Speed, but not much else.