The game was a little confusing at first and I didn't really know what to do or how to do things, but after a few tries I figured how the bubbles and cauldron more or less work.
Once you get going, it's actually pretty nice, if still a little confusing. Like I couldn't really figure out if more bubbles meant stronger monsters out of the cauldron, or why the green bubble bush kept jumping whenever I jumped, but all around I did enjoy it once I got the hang of it! :)
I'd suggest adding a bit of signage - hold the player's hand a bit in the beginning, explain the mechanics ingame somehow and reward the player for discovering stuff, be it tossing bubbles around correctly, making monsters or jumping around on bushes.
Once the player gets going, it'd be nice to know how are they in terms of progress. You get a prompt for a new monster arriving, but there's no info on how far have you progressed, other than the rather opaque score in the corner. The game was pretty short and ended rather abruptly.
All in all, it's an amusing little game - good job! :)