Really Great! Visuals are really nice!
Very solid level making skills, you introduced mechanics well, I especially loved the stone slime with the music fade into breaking out of the stone.
Puzzles are very well made, all having a good "aha" moment to them.
The movement feels a bit stiff, especially with the fixed jump height. It can be also a bit jarring to be moving immediately when you switch colors, especially when coming out of the bat you may jump as the slime when you don't want to. There could be a little buffer or animation showing you switch so you have time to react. This combined with the fact that there seems to be some spikes placed randomly on some ceilings made a lot of quick unintentional deaths.
For the first few levels I don't think there was a way to tell who had the key, so it took some trial and error to see who had it when they died.
Very well made! Great Puzzles!