Marill

Marill's oil-filled tail acts much like a life preserver. If you see just its tail bobbing on the water's surface, it's a sure indication that this Pokémon is diving beneath the water to feed on aquatic plants.

Even after Marill swims in a cold sea, its water- repellent fur dries almost as soon as Marill leaves the water. That’s why this Pokémon is never cold.