An excellent idea with a functional mechanic and entertaining theme. The way the levels are developed is interesting, as well as the combinations that can be made. The only drawback is in level 5 because the goal box asks for a purple slime, but when you put all the slimes together a blue one is formed and does not allow you to finish the level.
Anyway, the game is interesting and simple, the combinations that can be formed with the slimes is its strongest point, as well as to make a strategy to put them together.
Excellent work!