One the interesting things about doing a "demake" is that you are often forced to attempt things you would normally never consider for the hardware. The Royal Chapel area in particular has lots of fancy 32-bit effects that aren't easy to replicate on the Genesis / Mega Drive

Here I'm using tile scrolling on the foreground to make the forest and platform scroll at different speeds. The foreground layer is also covering up the bottom half of the screen, so that the main clouds on the background layer behind look like they begin halfway up the screen

While my main focus for now is the base console, at some point later this year I do plan to start experimenting the the Mega CD/32X. For the former, the ASICS chip should be able to imitate the original sky quite nicely (as in the Sonic CD title screen).

Talk to @birt_shannon. I believe he can help you create a routine using assembly to achieve the sky effect you want.

@birt_shannon He's like a modern day Jon Burton!

This is just a first attempt and I have some ideas of how I could do things differently. For example, I might try and use some raster effects on the main clouds (like in the SNES Axelay game)

As for the 32X, I think it should be able to do it quite easily at 60 fps (and up to 256 colours!), so long as the base MD is handling the rest of the scene (the sprites and the foreground)

The framerate on that Sonic CD ASICS layer looks to be around 20-30 to me, so it'll be interesting to see if that is a hard limit for the hardware, or if I'll be able to do it at 60

The only person I know of to be actively programming for the Mega CD's ASICS is @_gf64 , and you can see some demos on his profile. I believe he does it all in assembly language, so I have another excuse stop being lazy and really learn it this year!😅

The smaller clouds at the bottom are animated sprites utilising shadow and highlight mode for the transparency effect

You can use two layers of clouds, one moving left and the other right. With the right speed, they will have the effect of 3d, I dont know if Im explining my self well... Two opposite clounds. <_> by moving on opposite directions has a 3d effecf but up