Sorry guys, but to me it seems highly doubtful that a store would sell a demo to anyone if it didn't get sent back. In my memory, I am absolutely sure that the three characters were lined up in battle. It may not have been an old prototype, but it most likely was one regardless.
Prototypes are so cool. Look at SMS...full of mysteries...
I agree, also look at Super Mario Galaxy's "Star World" in the demos that were available for play at E4All and some other video game stores. It seems like it would have been a totally different game. I like this picture on Good Egg Galaxy. It is very mysterious...
Now for Star World:
Very interesting indeed. I'd like to have seen that in the final game once you beat every file
with 121 stars for both Mario and Luigi.