I would like to see:
Tails, Knuckles or Dr Eggman.
Goku, vegeta, trunks or piccolo (from dragonball z)or chibi versions of them.
Mew, Alakazam, Mewtwo or Dragonite. (get rid of frickin jigglypuff).
ToeJam and Earl.
Prince of Persia.
Nights.
Maybe one of the monkeys from super monkeyball, altho i suppose they would be a bit useless.
Korok from zelda windwaker.
A moogle of some sort, just because they are cute.
One of the pokemon E4 champions or gym leaders.
Spongebob and Patrick.
Non nintendo chars:
Guybrush Threepwood! (I know he's not a nintendo/sega char but you know it would be awesome to see him doing his insult sword fights an all

)
Companion cube for the lulz.
Spyro the dragon.
Smokie or lunatic from ragnarok.
The angel and devil from Black and White.
We need MOAR!!