The game plays really well.
Few tips:
The mouse cursor was losing focus when clicking in the level, might want to use the "set input game only" or similar function when going from menu based input to gameplay, also good to set "focusable" on your widget button components to false to avoid them taking focus.
Maybe have the Lab as an unlock after your first run, or after you have collected 50 gems, to have the player be introduced to mechanics one at a time.
Maybe set the ooze's aoe effect (big green thing), to not rotate with the character, looked a bit weird, though i dont know how it would look if it did not rotate.
Otherwise, nice game, like the concept of having the clean up as part of the alchemy theme. Missing the shadow theme a bit (besides making the messes disappear )