This is brilliant! The reversal seems so obvious in hindsight and yet I've never seen it done. XD The game it made me think of, weirdly, is Radiant Silvergun - a shoot 'em up where you have all the weapons at the start of the game and can use them at will by pressing different combinations of the fire buttons. I also love what you've been able to do with a grayscale PICO-8 palette!