It's been a long time since I started, so nowadays I don't have the same interest I had in this game, but anyway if someone with enough knowledge and commitment got involved, I'd still be willing to help.
On the other hand, this project is not looking to recreate the
Game Gear or
Megadrive version, but to get the best out of this unlicensed port, so if I had the means I think it would be better to focus on the mechanics and level design.
Currently, I have the most efficient method for editing levels, but I don't quite understand the criteria for repositioning objects and enemies, and if I resize a level that has
Eggman or is a
special stage, it will appear without any elements.

I still find it strange that a game with such an interesting engine hasn't been decompiled and studied by now.
It would be great, remove the junk code left after the
rom expansion, discard unused
CHRs, optimize, the use of graphics for objects and enemies, and update the graphics compression for intro scenes to the one implemented by
Hummer Team in more recent games like
SF3, among other things.
So far I found repeated code from
Sonic's animations, in four different sectors and a duplicate of the
oxygen timer, from the
Labyrinth zone.
CHR tiles not used in the game, including some that belong to a programming block in the "
Somari Team presents" screen. Which was discarded in this version, plus the highlighted images are parts of that duplicate code.

This is an example of how you could optimize the use of enemy graphics in the first zone.

In the following file you can see how
Sonic's animations are structured, managing something like this manually is an inhuman task, instead, calculating these pointers for a compiler takes seconds, making it a reality to improve or change the player's animations.
ASM Animations (Pasebin)In conclusion, any of these optimizations would have a positive impact on the game, reducing the
rom size and allowing it to be played on cheap
everdrives, providing enough space to improve the programming or include new sound effects, without complicating with unnecessary hijack codes, not to mention that after the project is finished, this engine could be transformed to create new
homebrews.