Excellent game! Certainly one of the-- if not THE-- most polished games that I've played for this jam. With the out of the way, I have some ticky-tack feedback of things that I noticed. But my jumping was actually bug-free!
1) Wanted to pause the game so I pressed escape (was in level 2). It brought me to the main menu, but for some reason, after that pressing the play button would only load the credits instead of the game.
2) The mud slime was the most satisfying to use, the vine slime was the least satisfying. I was ready to spit that out once I felt I didn't need it to progress anymore.
3) As some others have said, I felt a little directionless. The levels were quite large, and I think having some smaller early levels (with some fanfare at the end of each one), can help motivate players. In the first level, I wasn't sure there was going to be an ending.
None of these things detract from the overall excellent experience I had as a player, but since this game is taking off I figured I would throw my 2 cents in! Great work!