"It’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."
In the time between the Kanto and Johto regions in the anime, we got to see certain Johto Pokemon in the Orange Islands. The most prominent of all was Marill. Rumor among fans was that Marill was designed to be "an aquatic Pikachu", if on nothing else but cuteness factor. Its ears are so sensitive that it can hear the cry of a Pokemon a long distance away.
Marill's Basic Attacks are Bubble and Tackle, while its Special Attacks are Aqua Tail, Body Slam, and Bubble Beam.