Wow! Really great game! The hordes of slimes spawning around you were really difficult at first, but I had a ton of fun when I got used to it :). Combining the slimes turned out to be a very cool mechanic. Sometimes there aren't enough greens, but I'd say the randomness makes for an interesting challenge :).
I liked the world design! A lot of nice little details. But it got a little confusing on where to go after collecting the red and green keys for example. I feel like the world could be a bit smaller at that time of the game.
The adaptive soundtrack was a nice touch :). It gets a little annoying when the player moves around the transition point though. Nice nonetheless :).
The boss fight was fun :D. And I also enjoyed the ending ;). Very well done!