I really like your puzzle designs, none of them had me cocking my head to the side and trying to make the solution make sense after I beat it. I feel that in several levels you give part of the solution to people in the title, for example "Hold the Door" initially the level seems medium-hard, but if you think on the name a little bit, you figure out what to do.
I like that you have a puzzle in the map that uses the levels to block you from beating it at the beginning.
I wish that it was clearer to start with that you could not re-possess your body while your skeleton was burning. Maybe rework the first fire level a bit so that you see that your burning skeleton has to move around the player's body.
I think that in your accessibility options you should have a option for a plainer background. The option for turning off the animation is good, but for some people I could see even the un-animated background being too much.
If you are pressing a movement key while pausing the game, your character will keep moving in the direction of the key that you pressed, even while the game is paused, and even after you release the key, your character will keep moving.
I have an idea for the skeleton snake, having either a heart, or some other item, increase the size of the snake when the snake head runs over it.
I like the art in game. It feels consistent and, this is probably based my preference for retro art, looks really good.
I really like your game so far, the puzzles feel well though out and well designed. I would love to see this game when it is finished.
-R