I was playing this game at work for days and days, creating challenges for myself.
Guess what... It's possible to reach the end without spending a bullet and without taking damage (this is on hard mode).
The only enemy with mandatory death to finish the game is the final boss.
I had to test MANY times to find the right move.
It's a very fun game. I hope there will be a new version one day.
Congratulations on the project!