One thing worth fixing as you continue forward with developing is the viewport.
The game opens in fullscreen, and deviates from the aspect ratio of the GB screen, as well as insufficiently upscales the imagery. It seems to be the case that it was not designed with this in mind, since I can see part of the space between maps when I load in. Incidentally, the space between maps is a different color from your main palette colors.
Looking forward to future, more complete builds. I want to go on this adventure as the (incredibly speedy) cat.