I was impressed when I inspected the cartridge and saw a `.mid` file there. So this cartridge has also a MIDI player in it, deserves maximum score on music due to how hard to pull that of during a game jam. I wish you share the code of the sound related work on RIVES, to inspire others.
Also nice work on the cartridge cover. The game is also fun, when I saw it first I was expecting a Tetris like clone, but it's not like Tetris, it is unique with own set of rules.