Well, I went ahead and finished it. I'm not quite sure what to do with the background, whatever I could think of would distract from the foreground. Maybe a simple gradient will suffice.
This is easily one of the most epic things I've created in a long time:
(most definitely click to view the 800 x 600 version -- the full resolution of the version on my computer is 3200 x 2400)
I finished coloring Myrxus and Danter this morning, and did their shading over a couple of hours this afternoon. Finally, I drew/scanned the "Hell Snake" and colored him as well. I'm not entirely happy with the stone bridge, but I think the lava's neat. Drawing each of those stones in the bridge took forever, and I got lazy towards the end and ended up just drawing jaggy lines all over the place.
Finally, I added glowy/gradienty effects for the various heroes' spells and weapons.
I know the perspective is not perfect on the characters (first, you would see the *back* of the Hell Snake if he was really facing off against the heroes), and the anatomy may be lacking in the heroes. I feel I get a little better with the cel shading everytime I try, but I still have a hard time making things look voluminous ... I can probably blame some of that on my line work.
I do think the wonky perspective does have a charm to it, makes it seem more like a folk painting than an image of an actual event.
P.S. I should take time off of work more often!