Very cool game, the idea of using the overlap to determine the hitbox is very nice!
The graphics and overall gameplay is smooth as well, and the juice is working!
One thing that left me a bit frustrated was the feeling that my powerups (esp. damage) did not really do much? I was expecting to one-shot the bats at least after 1-2 damage ups (number did go up, but I did end up not really feeling the powerup).
Anyway, minor gripe for what is a superb entry!