I created these things called boomerang blocks in the castle that leads to level 4 in my quest. (If you play my quest when I finish it, you'll know what they are because they have a boomerang on them). My first one, when hit with the first boomerang turns into a push block. The next 2 boomerangs makes it a floor tile, my next boomerang will be (on the side of a mountain) boomerang 1: mountain tile, boomerang 2: cave, boomerang 3: stairs that lead to a heart piece.
:moo: - does this look like it's from harvest moon?