I posted this in the create-a-stage lol.
2d version:
The stage starts out 2d. There is one big main platform in the middle, and a little one in the top right. Goombas, turtles, and other koopas come into the level from the right, and some of them appear on the top right platform and drop down to the lower platform. They pretty much just walk by, but if they touch you they can hurt you and if you have high enough percent you can get knocked off the stage.
3d version:
After awhile, the stage turns around into a 3d stage. The big lower platform changes into 2 small ones and the top right platform turns into a bigger top one. In the 3d stage, the koopas still drop off of the top platform, but the ones that came from the right in the 2d part, they now come forward/towards you.
I know its not the best level design but I bet some kind of super paper mario 2d to 3d stage should be made.
Anyway, What do you think?