I wanted to delay the release of this until a split disassembly of Sonic 3 was released, but I changed my mind, for a couple of reasons. For one, since I wrote this in literally two hours, it's not to be considered "final" by any mean (even if it completely works) and I'd like to hear some comments/feedback/opinions about the editor itself, if it's user friendly, and so on; furthermore, it's not that hard to use it without a disassembly anyway, as Sonic 3's Special Stage Layouts start at location 2531552 ($26A0E0) in the S3&K rom, and they take 1032 ($408) bytes each (1024 ($400) bytes for the 32x32 ($20x$20) field, plus 8 ($8) bytes of header, which interestingly enough is after the data).
Sonic & Knuckles' Special Stage Layouts instead are compressed according to Varion's words, so they're not directly editable yet. I'm 95% sure that they're compressed in Kosinski so you should be able to use TSDC, though I wouldn't bet money over that.
Now, how to use it. Type the filename of the stage you want to edit and press "Load". To create a blank new stage just give it a filename that doesn't exist yet and press "Load" anyway. It will create a new blank layout with that filename. To save a layout just type the filename (or keep the one you loaded) and press "Save". This was easy.
Below there are three "palettes", to say so. You can assign a kind of ball to both the mouse buttons and to the wheel. This should allow for fast editing. Sonic's icon isn't a placeable object but it's used to set up the starting position. Note that nothing prevents you from setting the start position inside a ball, but don't do that, it's stupid.
Then you can decide the starting orientation, and there is another way to change the starting position if for whatever reason you don't like to click on the layout. Finally, you can set the rings needed to achieve a perfect. Yup, that's not automatically calculated so have fun with that. Right now I limited it to 255 because all the existing stages store it as a byte, but I think it can be extended to
The exit button is huge for a reason, it helps you remember where the Special Stage ends, otherwise one would be tempted to put stuff in the wrong place.
Well, make sure that your resolution is higher than 1123x793, and have fun.
DOWNLOAD LINK (1.00)
DOWNLOAD LINK (1.01) (updated 2009/10/24)
DOWNLOAD LINK (1.02) (updated 2009/10/25)
Note: this program, like all my other programs, requires MSVBVM50.dll, and can run in Windows 95 or better.