@Naz: Who ever even mentioned Banjo? And why is Sora 'completely unreasonable'? There are LOTS of reasons why he could be in the game.
There are tons of other Nintendo characters it could be:
-A couple more Pokemon (Haunter plz )
-Waddle Dee
-A guy from NES Baseball
-Chibi-Robo
-Elite Beat Agents
-King K. Rool
-Kremling
-Bomberman
-A snack that smiles back (GOLFISH!)
-An Animal Crossing character (Guaranteed because, there is a level but no character yet. I would want Nook or Jingle.)
-Evil person from Kid Icarus
-Birdo!!!!!
-Star Wolf
-Most likely Falco will return
-Baby Mario and Luigi combo (Luigi standing on Mario's head)
-One of the many bosses from Mario Bros. 2 (aka Doki Doki Panic)
-Jigglypuff will likely return (whether we want her or not)
-Geno
-Mallow
-Kooper
-RIDLEYYYYYYYYYYYYYYYYYYYYYYYYY
That's all I got...