Currently it's Squid Girl, Absol, Arietta, and Chester, as seen here. There probably won't be a terribly specific plan emerging until I get the details from her bonding thread concerning where the Trubbish are coming from and how they're getting to the ocean, but I'm going to go with the assumption for the time being that building some sort of barrier akin to a dam or a reservoir between the source and the water's edge will probably end up being the thing that works. So most likely the plan will be the involved parties and their Pokemon collecting some lumber from the forest in order to make something like that, and then doing so while Absol and the aggregate Pokemon of the other three hold off the Trubbish for long enough to complete the project.