I can understand that the water only levels didn't feel like they fit the theme because it is kind of like a jump you can only use in certain places. However, I feel like it was a useful mechanic because it was a simple way to add a lot to the game IMO. For example, since you can jump in the entire area it kind of gives a a "variable jump height" that acts like a quick double jump. It also let me easily make swimming and wall jumping. For the physics, I tried doing that thing where the character falls faster after the peak of his jump, but after adding in the trail I feel like I might've done the opposite. And for the moving platforms, I couldn't think of a good way to display where they can fly because they can go to the very edge of their boundaries, and in the end I didn't have time to make it look any different (besides from switching the color of the area). Also, I'm not great at coding moving platforms because they have to push the character if they go towards him so I settled for making the platforms teleport him up if he get's stuck in them. However, I am glad you ended up liking both the moving platforms and the physics. For the zombie art, I actually went to "Kenny's creature mixer" and then I separated his arms to be a separate object and gave the arm sprite an idle, jumping and falling frame. However, I doubt it's very noticeable because he's constantly moving. Lastly, for the music I went into WeVideo and looked for music until I found a good soundtrack, then I exported it as audio only and used it in game.
In conclusion, thank you a lot for your thoughtful analysis and feedback just like everyone else who commented. (-: