Cool idea and cute art!
At first I didn't really know what I was supposed to do and what each upgrade meant. After trying to fight enemies for a while it would usually form a horde that would follow me around, making it a lot harder to pick up the blood/xp items, and eventually causing a lot of lag.
A couple plays later I found that starting with maxing the bats seemed to be the best upgrade, which got me a lot farther, I got to 08:19.
The main menu animations and all the little effects in-game were really nice, overall it felt pretty polished! Good job :)