First off, you've obviously never felt Zelda's heel kick. On par with a warlock punch, if done right.
Second, this whole discussion has gone off topic. This is supposed to be about Shadow, no? And personally, I believe that Shadown would be best moved to an alternate costume of Sonic, along with perhaps Metal Sonic....in fact, I can see perhaps, different alternate costumes being different characters altogether, to save space perhaps (ex, Marth and Roy would be the same char, with different costumes, and certain moves would be affected by alternate costumes.) This way Nintendo would be able to keep their "no clones" promise, as well...
So in summary, 3 third party characters, right? Snake, along with:
Sonic (w/ Shadow, Metal Sonic, MAYBE Tails/Knuckles/Amy as alts) and
Megaman (w/ X, Zero, Bass, Protoman, .exe as alts)
are what I can see.