I recently acquired local copies of the original Genesis Sonic 3 and Sonic & Knuckles after noticing something very odd in speedruns- far-backgrounds with overlapping parallax elements. See: the trees before the Sonic path boss in AIZ2, the columns in the background of HZ, the trees in MHZ, the cave far-backdrop in LRZ, etc. Similarly, in MGZ and the boss of FBZ2, there are segments where one layer of background runs over another layer of background... on top of a raster-parallaxing far-bg. Now, I believe the Genesis only has 2 background layers and a sprite layer. A few of these effects could be explained away by creative use of large sprites, a few more by creative tile rewriting, but a few of them seem to be well and truly happening in the backgrounds in a way too complex to want to do by constant brute-force access.
One possible hint is that in levels where some other complex backgorund effects are happening (notably MGZ), the far-background is strictly raster-parallax with no intriguing overlap-parallax elements...
Any idea what's going on here?
