It was born from sludge transformed by exposure to X-rays from the moon. When its internal load of germs decreases, it dies.
– Pokemon Moon Pokédex
Alolan Grimer looks so happy, it’s like it’s looking to party. In Alola, the Grimer and Muk eat the waste, they become multi-coloured. Its become Poison/Dark type, which is a pretty good type combination, being only weak to Ground and immune to Psychic.