Basically any third party characters that don't actually have a long ( read: more than two console generations ), well established history with Nintendo. Bayonetta should not have gotten in, imo. Wonderful 101 shouldn't get in, but i'd be fine with Viewtiful Joe.
I don't want any super new characters from long running series to get in when there's still more important characters that haven't gotten in yet ( like Rosalina getting in before Toad for example.... )
I don't really want any Indie characters... not even if I like them. Sorry Shantae.
No more "wtf picks", call me anti-fun, but I think the cast should be fan favorites only. No Labo-Man, no wreckless Wii safety guy, ect.
And I feel like this shouldn't even need to be said, but for some reason, a ton of people are entertaining the idea instead of ignoring it like they should, but no licensed characters from TV, comics, and movies... Like Goku or Shrek, or even characters with reasonably good Nintendo connections like TMNT, Popeye, James Bond, or Scrooge McDuck ( I would, however, be fine with music from those games... give me the ducktales moon theme in the Mario Galaxy level, or Alleycat Blues in Wrecking Crew level )