Sad times
I recently bought a fully boxed copy of Sonic Chaos for the Game Gear and popped it into my Analogue Pocket. That's where I found the disappointing part. The frame rate dips all the way through, which makes it feel a bit funky to play. It reminded me of the old Mega Drive Sonic games running slow on PAL machines.
It is not the end..
So I decided to look into why it happens, and whether it could be fixed.
It turns out it isn't a PAL thing. The Game Gear runs at 60 frames a second everywhere. In busy moments the console simply runs out of time to get everything done before the next frame, so it skips one. It does the same on real hardware, so it isn't the Pocket's fault.
AI FTW
With help from Claude, I tracked down the worst offenders in the game's code and rewrote them to run faster. The biggest was a check the game makes every fourth frame on every object in the level, which explained the regular stutter. Nothing about how the game plays, looks or sounds has changed.
The result is roughly half as many dropped frames across every zone. It isn't perfect, and the busiest parts of Aqua Planet still chug a little, but it feels much smoother to play.
Results
If you'd like to try it, it is available below as a ROM, make sure you own the game, keep it ethical.