Really nice idea, that extrapolates quite a bit of gameplay out of a somewhat simple setup. :)
Some very smart swaps, actually loled at stones <-> enemies; the final change is also really cheeky! Music is chill, love it.
Some notes i took while playing (see it as feedback that I would also give for a final game, I know that we need to cut some corners in game jams ;) ):
- Controls/info at the start is very nice; no need to read anything outside the game.
- Jump is quite floaty, it might be intended, but I would wish for a bit more control when falling down (e.g., just search for any video of the 100s that analyze the Super Mario jump).
- While the directional shadow works quite well here, you might also want to consider a drop shadow directly below the character. This makes it way easier to estimate your position (e.g., are you already over a rock or not yet)
- Player feedback for falling "sand": was surprised when they first fell (some hint that this happens, classic would be a small wobble before falling, but you might find something different)
- Took me a bit to realize that the character actually has health, some UI or display on the character would be nice there.
- Camera is very static and quite central to the player. Adding a bit of camera lag and moving the character down in the camera view a bit might make the game feel a bit more dynamic
- Characters slide very slightly when standing still (not a big issue, but I just died over and over when writing this feedback xD)
- Also enemies, some just died when I was waiting for a bit
- Love the walk & attack animation, has quite a bit of character for how simple/goofy they are (and that is meant in the best way possible) :D