I came across this little tidbit on newnet IRC in one of the various rom channels. It appears to be a very early test version of Sonic Advance 2, complete with 9 somewhat working levels, and 4 usable characters.
First off, the title screen seems to either not be made yet, or replaced with this intro coded by the people who dumped it. In order to escape the "eternal" debug mode, you most hold down and then soft reset the rom. Holding down until the screen is displayed. Afterwards, you can change into any object with the A button, and character with the B button:
Sorry about the crap quality of this picture, I relized afterwards about the snapshot feature in visual boy advance.
and bring up this debug menu with select:
From here you can access any level with any character. Amy is listed, but not present, instead she is replaced by the new character "Cream":
Cream is a rather strange character, and haven't found any real use for her as of yet.
I don't know whatto do at the boss of this level, he comes down from the air, then sits there, and you have to reset or go back to the debug menu to escape it.
Here's tails in the very incomplete fire level.
Sonic in the music level. (the only level where you can complete both acts.
The only playable acts are:
08 (Leaf Forest)
0A (Hot Crater)
0D (Music Plant)
The rest instantly crash the game to a black screen and a high pitched noise.
Download the ROM here and see what you can find. I suggest the Visual boy Advance to emulate it.If there are any good hackers out there, please look into hacking this as a project, because I want to know if there's a real title screen or not.