The main mechanic of having a multiplier that can also give you negative effects works really well, but I think it needs to be communicated what possible effects there are and their chances. That would make it more strategic and make negative effects feel more fair, rather than getting unexpectedly hit with -70 hp.
The evil cookie looks amazing, but I have to criticize the inconsistent pixel size. I think it would have looked better with everything on the resolution of the evil cookie.
Great job though, especially doing this on your own!