So I've been watching your videos for a while and am amazed by the programming feats you've accomplished. But one thing I've been wondering about is the Sonic 3D Blast special stages. How do those work? Is it a similar trick to that used in Mickey Mania, or something completely different?
I probably won't explain this very well... It would seem that the path used ray casting, and the rate of each individual line's horizontal scrolling is based of the distance (like a racing game). I don't think the background uses the trick in Mickey Mania. It doesn't shrink as it gets farther away. It scrolls more like Axelay on the SNES. The effect probably has some thing to do with skipping lines in the texture at the top and repeating them near the bottom. But that's just my guess.
My guess would be the background (lava) is made the same way as the Mickey Mania effects and the path is a psuedo 3d road like track (like you would see in a racing game).