Heroes
FFI: One of the other WOL, maybe a female.
FFII: This one is a bit tough since the other characters were all meh. Maria, Leon, Mindu.
FFIII: Hmmmm. Ingus maybe?
FFIV: Edge, Kain, Rydia, Polom and Porom (maybe controlled at the same time?) and Tellah.
FFV: Galuf, Faris, Xezat.
FFVI: Celes, Locke, Shadow, Mog.
FFVII: Tifa, Cait Sith, Aerith.
FFVIII: Rhinoa, Quistis, Zell, Laguna.
FFXI: Beatrix, Vivi, Dagger.
FFX: Lulu, Wakka, Riku, Auron.
FFXI: ???
FFXII: Balthier, Basch, Fran.
Villains
The antagonists are a bit tougher since there only tends to be one major villain in each game, any others added would be mostly "minor".
FFI: Maybe one of the Four Fiends?
FFII: The Light Emperor, Emperor (Demonic), Dark Knight
FFIII: Xande
FFIV: Zemus, Zeromus.
FFV: Enuo, GILGAMESH!!!
FFVI: Gesthal, Ultros
FFVII: Rufus, Hojo, Genesis, Jenova.
FFVIII: Edea, Adel.
FFIX: Garland, Necron.
FFX:Sin, Seymour.
FFXI: ???
FFXII: Vayne, Cid, Other Judges.
Hmmmm.
Dissidia II - Can't wait!!!