Marill is a small, bipedal, blue mammalian Pokémon. It has a nearly spherical shape with a white underside, and round ears with red insides. Its arms and feet are short and possess no visible digits. It also possesses a zigzagging black tail with a blue, bubble-like ball on the end of it. The tail's jagged appearance originally led people to believe that it was related to Pikachu. Marill's tail is flexible and configured to stretch.
Aside from being able to swim well, it also has excellent hearing. It has water-repellent fur that allows it ease of swimming and reduces friction with the water. The end of its tail, which contains oil that is lighter than water, keeps Marill afloat.
Its tail can be seen bobbing on the water's surface while Marill dives underwater to feed on aquatic plants. When fishing for food at the edge of a fast-running stream, Marill wraps its tail around the trunk of a tree. Although the behavior of bouncing on its tail is more commonly characterized by its pre-evolution, Azurill, Marill may also do this on occasion.
This Pokémon is normally found in and around fresh water.
Marill are herbivores. Its diet mainly includes water grasses on riverbeds.
This Pokémon was unavailable prior to Generation I.