Harvest Plushies are little Pokémon statues with exclusive textures that you can place in your claim. Simply right-click the plushie where you want to place it. To pick it up again, just right-click it while crouching.
This will give you 3 Harvest Plushie Keys to use at /warp SeasonsIsland
Plushies in the chest are randomized. You can see all possible options by left-clicking the chest.
Too many plushies in a single area can be laggy, please limit the amount of plushies within visible distance to under 150. If you have more than that, you can split them up in multiple locations, as long as there's a few chunks of distance between them.