The idea is pretty cool and matches the theme well. I really love the graphics and art style. They go well with each other. However, I think the mana bar is a little bit restrictive, even with the leaves that instantly recharge the bar. The rate is slow, and there is little to no point that the player should just stand in one place for a long time just to wait for it to refill. The scaling of the sprite mask in accordance to the bar did not help :( Also, due to be restricted like that, I could not get a good grasp on the level layout. Lastly, there was this high platform at the top that was too far away from any other platform - this made the jump from that one into a blind jump. Luckily I guessed correctly and went hard right.
Pretty good game though. I hope that you would understand what I was trying to point out. I also made my Jam game with the same mechanic, but I was a little bit less restrictive with the sprite mask mechanic. I would love to hear your opinion on this though, even though I myself have already thought about the sprite mask implementation a lot.
Much love <3