@ SonicMario:
Hmm...I think putting Resetti, Plusle & Minun, and Balloon Fighter is kind of stretching it, but I think the rest of the list is reasonable. (Now if only we could submit these to Nintendo and HAL Laboratory).
Here's mine, (if a character's name is italicized, that means I only want them as a palette swap):
Mario
Toad
Mr. L
Dr. Mario
The Shadow Queen
DK
King K. Rool
Yoshi
Baby Mario (doesn't matter to me if he's alone or paired with Baby Luigi, I'm okay either way)
Wario
Captain Syrup
Kat and Ana
(pirates vs. ninjas, anyone?)
Pokemon
Blaziken
Sceptile
Empoleon
Monferno
Gallade
Dewott
Pikmin
Louie
President
Steve
Earthbound/Mother
Paula, Jeff, or Poo
Kumatora
Classic Characters
Little Mac
Third Party
Mega Man
Proto Man
Returning Melee characters
Mewtwo
TMNT, (I know it'll never happen, but ...)
Leonardo
Nightwatcher/Raphael
Usagi
I think I got a bit carried away with my list, but I don't think it's completly unreasonable.
@MnSG: I'll come back later, when I get a better understanding of Victini and Zoroark.