Once you get to the Bleak Beach area in Pokemon Pokopia, you’ll find yourself walking across a tar-like substance that seems like toxic mud. Using Water Gun will do nothing. That’s because eliminating it is tied to a character you’ll meet as part of the story in this section. It’s only after you find Piplup and make friends with the character that you can get rid of that Pokemon Pokopia problem.
How do I clean up mud with Piplup in Pokemon Pokopia?
The key to eliminating all the mud in Bleak Beach in Pokemon Pokopia is to advance the story until you’ve gotten rid of the water surrounding the Pokemon Center ruins, eliminated the water at Meowth’s habitat, and crafted two glowing mushroom lamps for that character’s home. Meowth will then complain about the mud nearby and explain a Pokemon used to live around there who could handle dirt. You then get a hint as to the habitat that character might like.

There’s a good chance you’ll already have set it up prior to this, which will make the next step easier! Piplup will move into Hydrated Yellow Tall Grass. This means four grass spots (made with Leafage) next to water. After having the conversation with Meowth and setting up a spot, it should onl be a few minutes before the water starter moves into the habitat.
Once that happens, talk to Piplup and ask the character to follow you. Walk to Meowth’s home, and the water type will use Bubble to start the cleaning process. Use Water Gun on spots with bubbles, and the mud will disappear. If you walk around this whole area with the character, you can get everything tidied up (and collect things like seaweed and seashells as you do). Note that Piplup will get tired if you decide to clean up all of the areas in Bleak Beach immediately after finding the character, so have some berries or beans on hand to feed your lil’ buddy.
Pokemon Pokopia is available for the Switch 2.