I imagine we'll get Mewtwo and the return of Pokemon trainer (perhaps using Mega Evolutions exclusively).
Jigglypuff will return, and Lucario will find himself dumped as they have to cut down on clones due to the stupid 3DS version.
The ONLY reason people think Lucario is a clone of Mewtwo from melee is because of Shadow Ball/Aura sphere. Their play styles are COMPLETELY different. Mewtwo wanted to avoid people as much as possible, Lucario involves getting in and having as much CQC as possible.
Pikachu mewtwo Pokemon trainer are the only ones in 100 percent.
I've not seen any footage of Mewtwo or Pokemon Trainer, though I may be behind.
The creator said he doesn't want to bring back all old characters so I feel jiggs is gone.
Not a chance. Jigglypuff (this isn't a text message; type out the whole goddamn word like an adult) was one of the original characters and is massively popular overseas. It will almost definitely return.
As for new Pokemon, I'm going to assume a representative from the newest generation, like how Lucario was added because it was a highly promoted 4th gen Pokemon or how Pichu was in Melee because of 2nd gen, but there haven't been any similarly highly-promoted 6th gen Pokemon. So, my guesses will be: A) Sylveon - I lied a couple of sentences ago. This has been a highly-promoted 6th gen Pokemon, certainly the most highly-promoted one. I would have reservations about a non-humanoid combatant just because of the whole question about holding items, but Ivysaur already proved that wasn't a problem. This could be pretty great, and it's Final Smash could summon all of the other eeveelutions! B) Mewtwo - Not a 6th gen Pokemon and technically a returning character, but it'll have something now that it didn't used to have: Mega Evolutions. Mewtwo with its Mega Evolutions have probably been the most highly-promoted 6th gen things other than the new Pokemon themselves and more than even most of them. It'd be a way to cater to nostalgia by going with an older Pokemon while still introducing elements of the latest games.