I drew up some tiles for the first subterranean cave section, which you can see here:
I’m still feeling pretty tenuous about my ability to create not-terrible-looking sprite art, but I figure the important thing for the moment is that it exists at all. Looking pretty is a problem for another day.
Attentive viewers will also notice a background-fade effect during room transitions, more or less ripped off from Super Metroid. It’s important in my case because I’m using full-screen background images, and to change between them smoothly requires a fade out.
Finally, I tweaked the mapping system to accommodate non-rectangular room outlines (although they are still screen-space aligned). This isn’t strictly necessary, but it does heighten realism a bit and allows for more interesting level design.