A simple forest tileset with feathers as decoration on the foreground. I tried to make them darker to not confuse the player with the real power-up.
If you want to use it, I recommend you to use this tileset in a level where you see for the first time the feather power-up in your hack.
Also, the layer 3 looks better with the 'wave' HDMA, so I recommend you to use this too.
This set's ground reminds me of Lemmings and the default palette's low contrast but lifelike colors remind me of a modern indie game's art direction. The feather's green tinting is well-done to blend it into the scenery on both layers, and the clear brown lowlighting adds some color variety to the bushes. Likewise, the yellow highlight on the ground feathers break up the dirt quite nicely. I do like the fact that the qualities of the small grains, berries, and holes in the set also build upon that "indie game"-inspired look and the two major varieties of slopes were included.
Despite the various tree frills, I do feel giving a few more tiles letting the player make the base line of the leaves have varying heights would be the perfect final touch for this set.
In usage, I feel a level introducing flight, making heavy use of flight, having a lot of airborne enemies, or a lot of bottomless area would appreciate this aesthetic. Even if the player changes a lot else about Mario or the feather, it would at least be a perfect nod back to SMW in a level involving learning to fly.