I made a post regarding this subject in the official character discussion thread, based on which characters had evidence within the game itself that supported their already likely returns. I believe just about every character on this list is practically a guarantee. I suppose I'll just copy it over to here.
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Meta Knight:
This picture. I'm going to be referring to that one a lot, mind you. This is a bit of concept art Sakurai posted on twitter. Here, we can see a number of veterans who were previously in Smash, including ones that have yet to be confirmed. With the confirmation of Zero Suit Samus, probably the least likely to return out of all the characters on the concept art (that's not to say she was unlikely at all; just that she was the least likely in that group of very likely characters), I think the picture is solid evidence in the favor of the remaining characters. Now, in regards to Meta Knight, not only is he part of this concept art, but the Halberd stage, a stage that is very closely tied to him, is returning. Add all that to a character who literally has no reason to be cut, and I think we have a character who's return is practically assured at this point.
Wario: Wario is another character who appeared in that concept art, which gives him a very strong case to return right off the bat. Couple that with the presence of the Ashley and Waluigi Assist Trophies, both of which have the Wario symbol, and Wario is a near guarantee.
Mr. Game&Watch: Again, another character who appeared in that concept art. There isn't exactly much else in terms of evidence, but I think this is enough to say he's safe.
Captain Falcon: Samurai Goroh returns as an Assist Trophy. I don't think there's any reason to doubt Captain Falcon now (not that there ever was).
Ice Climbers: The Polar Bears from Ice Climbers appear as enemies in Smash Run. Despite the Ice Climbers presenting some technical difficulties, I'm quite confident that those issues have been fixed and that they will return once again.
Ganondorf: Link and Zelda retain their Twilight Princess designs, despite Skyward Sword being the more recent game that is clearly being heavily referenced in Smash. This would indicate that Ganondorf, a character who did not appear in Skyward Sword, is returning, as otherwise there wouldn't be much reason to not update Link and Zelda to match their more recent appearance. (Thanks to @
MorbidAltruism for pointing this out)
Jigglypuff: A rather interesting observation regarding the sleep mechanic in the game strongly suggests that Jigglypuff is returning. This observation is explained
here, in better detail than I could provide. (Thanks to @
True Blue Warrior for bringing this to my attention, and @
LancerStaff for making the original post.)
At least one of either Ness or Lucas: There are Mother themed items present in the game. Unfortunately, this doesn't really tell us which one of Ness or Lucas is returning, but I do think it's evidence enough to show that at least one of them is. If it is only one, I would say it'd be Ness. However, I'm thinking both will be back regardless.
