Really? You can't think of one villain for XII?
*FFI - Black Mage WoL/Chronodia
FFII - Maria/ Borghen
FFIII - Arc/Xande
FFIV - Kain/Zemus
FFV - Faris/Gilgamesh
**FFVI - Celes/Ultros
FFVII - Tifa/Rufus
***FFVIII - Rinoa/Adel or Edea
FFIX - Garnet/Beatrix
FFX - Yuna/Seymour
****FFXI - Aldo or Create-A-Character/Shadow Lord
FFXII - Ashe/Vayne
*Chronodia only appears in the PSP version, but instead of choosing only one of the four fiends, Chronodia would serve as a representation of all four. He/she/it/they would just need a human form like CoD. But if only one must be chosen, then Lich if for no reason other than the fact that he's the most humanoid.
**Ultros would need a more humanoid form. I really don't know who other than him unless Gestahl could stop being old and start being more badass.
***Edea would make for a better character, but Adel's an actual villain. But Dissidia I didn't seem to care if a character was good and controlled (Golbez and Jecht), so I guess Dissidia 2 shouldn't either.
****Create-A-Character would actually be true to FFXI's hero. But Aldo could actually be a canon character. Plus, he's in the opening movie, so fans wouldn't have to go "who the ******** is that" like they did with Shantotto.