Yeah Dissidia has the main protagonists from FFI-FFX (10 chars), the main antagonist from FFI-FFX (10 chars), Shantotto from FFXI, and Gabranth from FFXII. That's...
Warrior of Light (FF1) andGarland (FFI)
Firion (FFII) and The Emperor (FFII)
Onion Knight (FFIII) and Cloud of Darkness (FFIII)
Cecil Harvey (FFIV) and Golbez (FFIV)
Butz Klauser (FFV) and Exdeath (FFV)
Terra Branford (FFVI) and Kefka Palazzo (FFVI)
Cloud Strife (FFVII) and Sephiroth (FFVII)
Squall Leonhart (FFVIII) and Ultimecia (FFVIII)
Zidane Tribal (FFIX) and Kuja (FFIX)
Tidus (FFX) and Jecht (FFX)
Shantotto (FFXI) and Gabranth (FFXII)
That's 22 characters. Here's a trailer
http://www.youtube.com/watch?v=tRdUffpPJz0
And I agree that Cloud and Sephiroth are abit overexposed. Don't get me wrong, I like Cloud and Sephiroth as much as the next guy but it's time other FF stars got to bask in the spotlight.