Nice game! Good enemy variety, neat UI and graphical design, and overall a solid submission!
There is one thing though that i found to be a bit... overpowered? The penetration upgrade made it so it was impossible to lose, and also it seemed to be able to hit the same enemy multiple times. So that enemy that you hit and transforms, i could kill it with a single shot (both of them). Not sure if it was intended, but it makes it a bit unbalanced I'd say.
Cheers! ;)