The real final boss, as in (SPOILER)Necron? He isn't that hard, is he? I used Zidane, Dagger, Eiko, and Vivi.
Zidane: Attack/Grand Lethal when possible
Dagger: Heal or summon Bahamut
Eiko: Cast Holy or summon Madeen
Vivi: Cast Flare or Meteor
Just use Dispel whenever he protects/shells himself and you should be fine.
Lather, rinse, repeat...