Cool game.
The fundamentals seem alright. The contrast between the background, the player's hitbox and the bullets is pretty clear.
I played the game with my trusty Mayflash F101 and it works perfectly, but I couldn't get the bomb to work for the life of me. I also noticed that the bomb input is missing from the controls tooltip at the bottom left corner so I assume it's a work in progress. Cool UI by the way.
A larger problem is that I couldn't remap the controls. The default controls are fine otherwise. Perhaps the focus mode transition could be a little bit snappier.
The boss was pretty cool. Modular damage is an awesome mechanic and I think you should milk it for all its worth. The game in general could use more sound effects for explosions and when collecting items.
I'm not sure what the collectibles are meant to do either since there's a checkpoint system instead of a more traditional life/continues mechanic, but they should probably make a little sound and increase your score for when you get around to implementing that.
I think my biggest note would be that damage feels a little useless because most enemies are tough enough to shoot before going down so there's little benefit to actually killing them. This is a problem because shumps have a recurring problem where the most optimal way to play them is to stay at the bottom of the screen doing nothing and venturing forth to defeat the enemies before they can cover the screen in bullets is often the best incentive.
That's all I had to say for now. I look forward to finding out what a "Marras" is supposed to be. Keep up the good work.