I played the Linux version on Linux.
I did not progress past the second level, because I found the jump too difficult, and retrying requires walking the entire level from the beginning. I did retry several times.
Overall: interesting platforming concept. It was not clear how to activate the sand boy mode, but it seems it's a combination of jump and E.
Fun: there's a lot of walking in the second level. Feels a bit unfinished.
90s: I played every other game in this Jam before saying this, but this is actually the least "90s" out of all of the submissions. The art is absolutely beautiful, but it's too fancy for the capabilities of 1990s hardware. I also dislike the screen filter.
Visuals: I'm amazed at how smooth the character animation looks.