I used Zell, Rinoa, and Squall. They were level 100 with max strength and HP. I first converted the Gilgamesh card to 10 Holy Wars. Then I made my characters as fast as they possibly could be. First Strike is a must. All characters must have their most powerful Limit Breaks ESPECIALLY Squall. A level 100 Eden is a must. Use the Fat Chocobo card to make 100 Luvs. then use it on Rinoa so she'll have max comp. with her.
During the battle, I cast Aura on all my characters and THEN used a Holy War. It won't work if you do the opposite. You CAN draw spells during this period but I didn't want to risk it. Use the Limit Breaks continuously for Zell and Squall. Rinoa should just cast Eden for each round. Hopefully Squall will use Lionheart for each round. However ZELL is the prime contestant of this battle, mainly due to his "Armaggedon Fist". What this is a continuous string of attacks using his Limit Break. For example, quickly input Punch Rush then Booya then Punch Rush then... At max time (13 seconds) I could unleash upto 300,000 pts of damage in ONE limit break. You have to be quick with the input though. When the Aura wears off, you can either draw spells or heal if anyone is hurt. When the Holy War wears off use another then use Aura and repeat the above until he falls.