I just played it, and I have to say I really like the idea. I am a huge fan of magic spells in games and a vampire survivor game with magical elements would be sick. Also, the fact that the water spell is a fish is just awesome.
Improvements: - sounds obviously, but you are probably aware of that. - a bit more juice, maybe a bit of screenshake when getting damaged (I think you already implemented a short time freeze when getting hit, which is nice).
Also a quick question? Are the different slimes weak against certain spells? E.g., is the red one weak against water?
Besides that, I am really interested to see where you guys take it from here. Good job!