In Panic in the Park!, when Cerise Park was experiencing an unexplained food shortage, Grimer was one of the Pokémon affected by the hunger and driven into fighting the other Pokémon. When Goh's Golurk went out of control due to the seal on its chest being removed, Grimer helped protect the Cascoon from the flood caused by Golurk's rampage, allowing them to evolve into Dustox.
In Big Brother to the Rescue!, Grimer caused Cerise Park's water stream to be polluted by bathing in its water source, as it had given its previous cave home for Froakie to inhabit. As such, Goh, decided to help build Grimer a new home in the form of a pond that it could bathe in without polluting the stream. The pond was quickly completed, with Suicune helping to clean up the polluted stream afterwards.
Grimer is a friendly Pokémon who doesn't intend to cause harm to anyone, but can end up inadvertently causing problem to others around it, as seen by it polluting Cerise Park's water stream without meaning to. It also was considerate enough to offer its old home to a newcomer, having made friends with Froakie soon after its arrival in Cerise Park.
