@Super Smash Bros. Fan: I noticed that you checked out my roster. Just a couple things to say...
Leon is known for chasing Falco, which does make him Falco's rival. And unlike Waluigi (who is deliberately a spin-off character), Leon has appeared in mainstream titles. I'm pretty sure that he'd operate differently from the other Star Fox characters.
For the Pokemon roster, I would replace Jigglypuff with Mewtwo if it weren't for the fact that Jigglypuff is a member of the original 12.
F-Zero, not too much to say there. The three characters that I've mentioned are basically the only best picks.
Starfy, maybe I should've separated him from the Nintendo Classics category, since that category is more for characters from the Game & Watch, NES, and Famicom consoles. A minor mistake that can be fixed up easily.
Bubbles and Eggplant Man are relatively fillers, but they do represent the classic Clu Clu Land and Wrecking Crew titles, both of which were developed by Nintendo. If R.O.B. could be made into a fighter, what would stop those two from joining the fray.
People have complained about me not including Takamaru, so something has been telling me that he's quite popular in Japan. I wouldn't know though, since he's a Japan-only character.
3rd parties, that has been tricky. I'd like to see Square Enix be involved, since the company did make some interesting Nintendo titles, such as the most recent Mario Sports Mix. Add the fact that the company also released popular Final Fantasy and Dragon Quest titles onto the DS. Anyway, Smash Bros. is primarily about the Nintendo titles, so it's pretty obvious that the 3rd party list would be limited to less than 5 characters.
To finish up, I was only trying to make a sensible roster, while not overflowing the playable character amounts with spin-off exclusive characters (Waluigi comes to mind). Without the 3rd parties, the roster adds up to 46 characters when transformations are excluded; 51 when transformations are included.
Basically, the roster probably won't be larger than 55 characters.