Love the Idea of having different gimmicks to fight each boss, The element of the "Random Gun" in the "Normal" fights is good, but all guns feel the same, there was no special property to each gun. Also, there is absolutely no feedback that lets you know if you are hitting the boss.
I dig the GB aesthetic, but it seems that you also add the object limit of one, if you rapid fire the guns they disappear, this with having no feedback makes the boss battle feel like you aren't doing anything to the bosses. Also, the controls felt super unresponsive
Making different bosses and different stages for each of them is super appreciated, and that effort needs to be noted.
Good job!