This is a pretty complete little package here, well done! That seems pretty hard in a jam, especially when making your own engine. I too made my own engine and this was the aspect I personally had the most trouble with, so I was impressed.
I think the central mechanic of throwing enemies at other enemies as the only means of attack is a pretty unique and interesting concept, and I thought the presentation was fairly well done. Starting a chain reaction of enemy kills was quite satisfying, although the sound effect when doing so was pretty painful.
One thing to improve would be game feel. Things like making movement have a bit of acceleration, using easing functions instead of linear motion, emphasising impacts, and adding screen effects. It's tricky to do in a jam setting, and easy to go overboard, but injecting just a little bit of juice can go a long way in making a game fun.
I'm also not sure it conveys the theme particularly well. Sure, the enemies technically serve two purposes, but the way its implemented doesn't really create any unique scenarios or decision-making opportunities, which I feel is an important part of what makes dual purpose design interesting. As I said before, I do think it's a good mechanic conceptually, it just wasn't utilised as effectively as it could have been.
That said, congrats on the solid showing!