It's impossible to tell, because we can't really know how everything is going to be.
But still, I like predictions and as far as the info we got...
Diddy: depends on if glide tossing is back / he can still pluck naners/how they work / how else he's different. if everything stays the same the range buff would obviously buff him a bit, and his more angleable upB.
Little Mac: we'll have to wait and see how his power-punch will work and if there are good characters that can get him offstage. he has a lot of super armor in his attacks so it's possible he can do well even against falco and others, as long as they can't get him offstage/gimp him...
Lucario: seems to be buffed a bit, so it might be save to assume he'll be around where he is in brawl (around high tier), but like many have said, there could be so many little changes with his attacks etc that could end up mattering a lot.
Dedede: who knows. if he doesn't get his chaingrab he could get worse than in brawl. since they probably didn't buff him too much
Zelda: no idea
Marth: better shield breaker is scary. if he stays mostly the same he'll be really good, as he's always been
Rosalina&Luma: no idea how this will work out. could be pretty good, could also be too much of a gimmick
Sonic: too few things known imo atm, could still be around lower mid, unless he got nice buffs (better frame data/kill moves/more grabrange?)
Toon Link: no idea
Peach: no idea
Luigi: no idea
Olimar: no idea (hopefully less annoying to play against)
Villager: seems really gimmicky. could be really good, could be too gimmicky with his slow and weird moves. but IF they work, they will be great.
Mario: who knows... I can't imagine Mario being good, lol, but maybe they will make it possible.
DK: no idea
Megaman: tbh, it looks like he could end up sucking (he has to take risks for most of his combat moves, so he'll either have a really good grab/projectiles or he'll suck) , maybe his special moves and aerials/smashes will help him out
Wii Fit Trainer: looks pretty decent. ~high tier?
Link: dunno, but his recovery still seems really bad..
Samus: who knows, she looked a little faster this time. Maybe if she'll get an actual kill move she could do something besides doing damage...
Kirby: no idea
Fox: no idea
Pikachu: no idea
Bowser: it looks like he has heavy armor on his jabs. and he's overall faster and his moves are different. i'm interested to see how he works out. he could end up being a decent fighter, but who knows...
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