Grimer is a slimy, amorphous Pokémon, born from sludge in dirty streams or seabeds that are exposed to lunar radiation. It has two large eyes with beady pupils and a gaping mouth with a gray tongue. While it lacks any visible legs, it does have two arms with three digits on each hand. Its purple sludge body contains a variety of pungent bacteria, which are so potent that it renders soil barren and incapable of supporting plant life. It is constantly oozing a bacteria-rich fluid from all parts of its body. Should it run out of internal germs, Grimer will die. Pieces of it often break off during travel and go on to become new Grimer. When combined with another Grimer, it produces new poisonous compounds.

Due to its lack of a solid form, Grimer is capable of squeezing into any space or crevices with relative ease. It uses this to penetrate sewage pipes and feed off of the filthy wastewater inside. Its population fluctuates based on the availability of waste, which is Grimer's main diet. It can be found in polluted lakes and streams, as well as within cities and factories where trash and industrial waste can be found. In recent years, thanks to efforts in environmental improvements and a decrease in their food source of waste, Grimer is now facing extinction.

Prior to Generation IV, Grimer and its evolved form, Muk, were the only known Pokémon that could have Stench as an Ability.

Forms

Grimer has a regional form: Alolan Grimer.

Grimer was brought to Alola to deal with the excess waste generated by the region's increased population. Alolan Grimer eats solid garbage instead of sludge; this new diet has caused its body composition and form to change. Alolan Grimer's body is green with a line of yellow sludge along its lower lip that extends around behind its head, a bright blue tongue, and small black crescent-shaped spaces behind its eyes. It also has two blunt "teeth" in its upper jaw, which are actually crystallized toxins formed by its diet. It is not known how to break down these toxic crystals, but direct contact with them is known to be dangerous. Lethal poisons leak out of Alolan Grimer's body when these crystals fall out. Because it produces and stores toxins within its body, Alolan Grimer does not produce a foul stench like Kantonian Grimer.

There are usually about one hundred Alolan Grimer found living near waste-disposal sites in Alola, assisting people in dealing with garbage. Alolan Grimer is widely used and a very popular Pokémon used in garbage disposal facilities around the world. Alolan Grimer is perpetually hungry and must constantly eat trash. If no trash is readily available, it will eat other manufactured products instead. In addition to garbage, Alolan Grimer preys on Trubbish and Garbodor; its introduction to Alola caused their populations to decrease in the region. They can also be found in the Coastal Biome of Blueberry Academy's Terarium, where Alola's island life is simulated.

Alolan Grimer and its evolved form, Alolan Muk, are the only known Pokémon that can have Power of Alchemy as an Ability.

Evolution

Grimer evolves into .

Alolan Grimer evolves into Alolan Muk.

(Source: Bulbapedia)