I got so happy when I read that Lightning is going to be in Dissidia Duodecim, and it got me thinking about who else I would like to see make their way into Dissidia. Who would make a good Dissidia fighter? 
 
Also, who would be the playable villain from FFXIII? It can't be Galenth or Orphan, so maybe...Cid Raines?

I still want them to bring in the Tactics cast.  Ramza vs. Delita/Weigraf/Ajora/Dycedarg/Zalbag?  Meliadoul vs. Vormav?  All kinds of crazy things they could do with that.  Also, it seems Tactics needs more character pages.

Edit: As far as the main series goes, though, I guess Auron would work.  Tifa would be interesting for some bare-handed fighting action, and I'd have to be insane to say I didn't want Vivi and the Black Waltzes in the game, but that's as much a Pipe dream as Tactics being included.

vivi.

Cid. All Cid's.

" Cid. All Cid's. "

Cid would be a great addition, but I'd like to see some more characters from FFVI make it in. Sabin was built a fighter and his brother Edgar would make his repertoire of tools a nice way to dispatch foes. Imagine auto-crossbowing dudes and then finishing them off with a chainsaw to the groin. Or just take Sabin and do his assortment of Blitz combos. Sabin > Zell, bottom line.

" Cid. All Cid's. "

Sazh
 
think of all the combos he could have with his chocobo

Moogles; just imagine their intensity! :O

Chrono, Sora and a Black mage.

it would be cool to see some of the characters for Final Fantasy Tactics

Barrett, Cid Highwind, Red XIII, Setzer, Locke, Shadow, Edgar, Sabin, Cecil, Kain, Golbez, and that is all I can think of.

I'd prefer to see Rydia, Tifa, and Seifer.
 
Also, Ultros must be in this game as a boss fight.  I DEMAND IT!!!
 
As for an FFXIII villain, Cid would be the most "playable" choice, I guess.  Barthandelus and Orphan are both too crazy in their true forms to be playable, and Barthandelus as Dysley wouldn't be as interesting.

They should have included Vanille and Hope from FFXIII