Dragonbreath
Smash Ace
Well, the Silver Sticker proves that there's no legal barrier. If Sakurai had to buy rights for likenesses, he wouldn't have bought Silver without Tails or Eggman. So we're defintiely going to see other Sonic characters, even if only as stickers/ regular trophies. And Gray Fox shows that he's not worried about letting a 3rd party non-main character be an assist trophy. So the only thing we can't reliably ascertain is that other Sonic characters have a chance to be playable.SonicMario has a point, and also consider how old that notice was from E3. Nearly over or has been over a year ago, so it may have been altered but i do believe that another sonic character will have his/her chance to shine no doubt about it.
Well, Sakurai can still surprise us. . .
Edit: @Forumla1: Those movesets are kind of hard to read. But I like Knuckles's neutral B.