- Voice actor: Michael Haigney (both English and Japanese)
Muk is a large dark purple mass of sludge, toxic fluids, and other filthy materials. Muk look very similar to its previous form, Grimer. The main differences are that Muk is larger than Grimer, and and has a wider mouth, dark gray tounge and it has two large arms and its eyes with black pupils are barely visible through the sludge. It is also usually shown with with a strand connecting its upper and lower lip when its mouth is open. The sludge it is made of is apparently less dense than water as it has been shown to float on it. Muk's height is 5'11" and weight is 66.1 lbs.
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.
The toxicity of Muk's form has reached the point where a single drop of it can make an entire lake stagnant and rancid. Its footprints are toxic enough for a person to contract Template:Wp if they are touched. Their infamous stench increases in the summertime, due to the toxic substances in its body intensifying. Their ability to exist in the environment without it becoming completely hazardous to other lifeforms may be attributed to their ability to actively control their toxins, as they would likely never want to deliberately pollute a river or spread any harmful diseases.
In the wild, Muk usually take charge of their family of Grimer and are very protective.
This Pokémon likes warm and moist places. Groups of them accumulate in dirty places, such as garbage dumps or sewers. They sometimes also reside in dirty back alleys of towns. Despite their penchant for thriving in dirty, contaminated places, they do seem to have a limit as to how much pollution they can tolerate, as no Muk lived in the Lake Lucid of fifty years ago until some work was made on purifying it.
- Main article: Pokémon food
Muk will eat anything that is already contaminated.
Ash captured a Muk in Sparks Fly for Magnemite. It was transferred to Professor Oak's lab. Ash's Muk is always trying to smother Prof. Oak. The first time Ash used his Muk in battle was in The Fourth Round Rumble, as a trump card against Jeanette Fisher's Bellsprout that had already defeated his Bulbasaur and Pikachu.
A Muk appeared in the opening of Destiny Deoxys.
Six Muk appeared in The Psyduck Stops Here!.