A nice little game. I like the addition of the gems which add risk on whether you should get it or not. Makes the gameplay very interesting. I also like your choice of art and music of the game. A good, fun little game overall. Good luck on the jam!
A couple of our play testers would avoid the gems outright since the original design was only negative affects. After we added other beneficial affects they started to gram the gems more. Then we just made a couple of levels where you were forced to get gems.