I've made some progress on the painting, thanks to my rudimentary understanding of dimensionality and lighting (and also thanks to years of amateur-level Photoshopping, plus my years of cartooning). This is far from a finished work, of course: the cave glow isn't right, Satan's teeth seem comically thick, and I still have to solve the riddle of Maqz's fur. But for what it's worth, this is as far as I got tonight (click on the image for full size):
So that's where things stand. Sean emailed to say he'd liked those first images of the painting; I have no idea whether he'll like the progress made thus far.
If nothing else, I'm developing a lot of respect for people who paint well. Controlling a brush isn't as easy, for me, as making a cartoon or doing a brush painting (which I view as a type of cartooning: maximal expression through a minimum number of lines). I'm using acrylic paint, and I've discovered that acrylic is so thick that it's very hard to make super-fine strokes. I may need to practice that technique on a separate surface if I'm ever going to get Maqz's fur and Satan's teeth right.
At this point, I kind of like how the painting looks when seen in its reduced size. The overall impression, though not perfect, is close to what I was going for, but all the flaws are even more evident in the magnified view. But I think that, ultimately, the entire cave is going to be suffused, on some level, with that infernal glow. As things stand, the lighting isn't where it needs to be. Fortunately, we're nearing the details phase: most of the major work is done.