Muk is a large purple mass of sludge, toxic fluids, and other filthy materials. It has two large arms that capture prey and its eyes are barely visible through the sludge.
Muk can have the ability Stench or the ability Sticky Hold. Stench decreases the chances of encountering a wild Pokémon when Muk is the first party Pokémon. Sticky Hold prevents the theft of Muk's held item. A toxic fluid seeps from its body, which can instantly kill plants or trees on contact. Muk has one of the highest attack points of all Poison-type Pokémon, losing only to Toxicroak.
In the anime
In the anime, Ash has a Muk after he caught it to restore the power of a town. He later used it to battle a Bellsprout used by a trainer called Jeanette and was able to beat it thanks to Muk being able to absorb all of Bellsprout's attacks, finally finishing it with a Body Slam.