The description you gave makes it sound like the Naruto fighting game on PS2. In that case, that's a big no-no. Nintendo will be crucified if they come up with something that unoriginal, especially for a title that millions are looking forward to.
Anyways, back to SSBM. Unlocking all the stuff in the game is a real pain. I had to help one of my friends with it because no one had game data that he could copy.