Well done! Interesting mechanics. One should note though that although the concept is displayed as the player phasing in/out of a second dimension, this is very close to semisolids in many other games that are ignored while moving up, but are solid while moving down. In other words, it seems like almost this entire game could be built in Super Mario World with lots of cloud blocks (except that walls behave differently, but this doesn't appear to be adding to gameplay much). But I do like this new take on "explaining" semisolids intuitively. Good work!

Minimalistic jump physics - sure, why not. Makes this game more a puzzle than a platforming game - which for this idea seems appropriate.

Only thing I dislike is that it uses "the ceiling is solid" for trolling in some levels, and in others you're expected to walk on the bottom of the screen, which in many other games would mean death. Would maybe suggest not doing that, but instead drawing solid lines around all four edges.