like people already said the mush set (especially the mush lamps, mush stools, and mush logs), the mushroom themed mario furniture (small and large mushroom platforms, 1-up and super mushrooms), leaf piles, the different rock themed DIYs that have moss customizations options, and some swamp-water or moss themed custom designs on the ground would work well. The upcoming keroppi themed furniture coming with toby's amiibo card (like the frog sitting on a lily pad table) as well as frog and bug models would work well too and make the area look more alive.