I went to the Best Buy event at West Bank and I can talk about some stuff I saw happen there. I played as Greninja, Villager, WFT and Bowser, so I can talk about them a bit as well as general Smash stuff.
Greninja's Shuriken cannot be charged, as soon as you fully charge it, he automatically throws it.
Down-Air does indeed bounce you off of people, and it's wonderful for following combos.
His FS starts off with him stomping on a trapdoor, and if it hits someone then the rest of the move occurs.
Substitute can spawn all kinds of objects. I've seen substitute dolls, logs, bricks, and even his FS's trapdoor. These items can be knocked around the stage as weapons too.
His up-air is like Samus's on roids, it's so fun to use, and has a really nice reach.
Shadow Sneak or whatever it was felt a bit tricky to use, I kept doing it wrong I think.
Villager cannot Pocket Megaman's charge shot, I tried and took the attack straight to the face. Might've just been bad timing though. Super useful elsewhere defensively though.
Lloyd Rocket has a bit at the end of the blast where it slowly starts to fall like a plane, before exploding.
Timber is really difficult to get off in a 4 player match, it takes so much time to get everything set up.
Bowling Ball F-Smash has pitifully small range, I'm assuming the fact that it falls is meant to make up for this.
Back-Air Slingshot CAN be reflected by Fox, I had it happen to me.
WFT's Sun Salutation is a really good projectile. Even the uncharged ones have usable knockback, and it goes quite a decent distance.
Volleyball/Soccer Ball Special can be hit by attacks and deflected I believe.
Hula Hoops fly off of WFT at the end and do damage after they've flown off.
A Sonic I fought used what looks like a new D-Smash.
Blue Shells are nowhere near as dangerous in this game as Mario Kart, they're actually quite tame. They can also explode on other items as well. I saw someone saved from its wrath by a party ball.
Ore Club weirdly has the Star Rod's sound effects? I guess the item must not really be finished yet.
All the other items with design changes seem to be basically the same.
Some guy with a big-ass sword is an assist trophy, he can be hit and stunned though. He just ran around and smacked people. Kind of boring tbh. I think this might be the Magnus guy people mentioned? I'm more of a Pokemon guy so IDK.
Another assist trophy looked like DK in a shirt and hat. This one made a wave of bananas fall down from above, which got a lot of laughs out of the crowd.
Xerneas showed up in a match in front of me in line, and it made the Mario and Rosalina near him glow with some blue-ish aura. No idea what exactly that did, I didn't have the best view.
Fletchling showed up as well, it just jumps forward on the ground and pecks people slightly. Really awful Pokeball.
Didn't get to play the 3DS version or Smash Run, people were on it too much but I heard Yoshi has some substantial changes on it, and that Sheik can aim her Light Arrows now? Didn't see either of these myself so take them with a grain of salt.
That's all I have for now I think, I'll be going back Saturday, so I'll see if I can unearth anything else then.