I would love it if it was a scrolling stage where it would stop at certain times and you got to fight in the area for a while. And when the screen started moving again you had to keep up with it., or die.
I also say this cause there's a few classic sots I would love to see for a fighting stage.
The beginning of most Green Hill stages, there's a smal hill that usually Sonic jumps on to get his first item. This could be a classic stage feel. Then we move on to one of the swing set spots, I reckon this would be a very cool part, and they shout have spikes down the bottom just to make it more interesting and make revolve around the swing. Then move on to a Loop Area, beating a character up in a loop would look awesome and because of the deal it be cool knocking them around in the loop, and fighting on top could be cool. Then maybe a ribbon area or a spot with all these spring items, trees and such, moving platforms. And then finally a Boss type area. with Robotnik coming through in one of his classic machines now and then.