Grimer was created when sludge in a dirty stream was exposed to the moon's X-rays. It is composed primarily of putrid, hardened sludge and grime. It smells incredibly foul, and can influence the abandonment of entire cities due to its polluting nature－even weeds don't grow where a Grimer has appeared. Grimer thrives in filthy areas, such as factories, garbage dumps, sewers and polluted water systems. It survives and matures by sucking up polluted sludge that is pumped out of factories, adding toxic waste to its already toxic girth.
Grimer can have the ability Stench or the ability Sticky Hold. Stench decreases the chances of encountering a wild Pokémon when Grimer is the first party Pokémon. Sticky Hold prevents the theft of Grimer's held item. It enters sewers and other areas with great ease due to its rubbery and semi-viscous body; for example, it can enter barred-off areas by slipping between the narrow bars. If you stick your hand in a Grimer, it will be very hard to get it out.