a Japanese poster reached the internets, and a closer look revealed all the villains that will participate in the game. most of these chars aren't officially confirmed yet by S-E which is why I wrote 'semi rumor'.
clean poster
edited poster
Full list as of March 2:
FF1 - Warrior of Light, Garland
FF2 - Firion, Emperor Palemecia
FF3 - Cloud of Darkness
FF4 - Golbez
FF5 - Exdeath
FF6 - Kefka
FF7 - Sephiroth
FF8 - Squall, Ultimecia
FF9 - Zidane, Kuja
FF10 - Tidus, Jecht
clean poster
edited poster
Full list as of March 2:
FF1 - Warrior of Light, Garland
FF2 - Firion, Emperor Palemecia
FF3 - Cloud of Darkness
FF4 - Golbez
FF5 - Exdeath
FF6 - Kefka
FF7 - Sephiroth
FF8 - Squall, Ultimecia
FF9 - Zidane, Kuja
FF10 - Tidus, Jecht