Nice and simple game but fun to play.
Upgrade seems to not work after the 4th upgrade? Bullet speed resets.
You can move right up to the enemy and stay just ahead of it to kill it without getting hit. Then just move over the top of it and repeat.
I won first try so had to replay and loose to see the upgrade screen.
Maybe have the upgrade screen on a win also?
Cool game tho well done 💚