A very enjoyable platformer! I really like how intuitive and easy to grasp it is to use the slimes to jump and attack.
One improvement could be to show some sort of slime counter, it is sometimes quite hard to keep track of how many you siphoned, especially in levels where there are so many (like the last level).
Also I didn't immediatly understand when I was sent back to the first level after losing my three lives, maybe adding a sound effect or an animation could make that clearer.
You can feel the care that went into the level design, and I had a lot of fun clearing them all.