HP:
100,000
Draw List:
Regen, Dispel, Ultima and Eden
Attacks:
Light Pillar (9999 to one), Quake, Meteor, Ultima, Physical
Attack

Stratergy
1) Squall should draw Eden. The second character should Aura Stone Squall (or lower his hp). The third character should use Holy War.
2) Next turn, have Squall use Doom Train. Follow this by Renzorukens holding triangle. Your support characters should attack or draw magic, mabye limit break (if they can). One Lion Heart will kill the Weapon.

HP:
1,161,000(With Squall Level 100)
Draw List:
255 Magic: 255
Attacks:
Light Pillar (9999 to one), Meteor, Ultima, Physical Attack, Terra Break (very strong meteor attack), Medigo Flame (9998 to all), LV5 Death

Stratergy
1) Have Squall, Zell, and a third character in your party, all above 90. Squall/Zell should have 255 strenght, and the third character should have DoomTrain.

2) Get at least 4-5 Holy Wars (get 10 by refining Gilgamesh).

3) Get 100 Death and Junction it to Stat-Def. Draw Death from Tonberrys
at the Centra Ruins.

4) Get Squall/zell down to limit break hp. Give one Auto-Haste. A third character should have Iniative and GF. Everyone should have item.

5) Have your main party go to the switch point in front of the fountain in Ultimecia Castle. Have your other party go to the east wing of the castle, in front of the art gallery, and proceed to the bottom left corner. Examine the grey thing to start a timer. Quickly switch to your main party and enter the chapel. Omega awaits.

 If you had junctioned Death properly, Lv 5 death will miss. Use a Holy War with your "item" person, and next turn, use DoomTrain. Hammer at the weapon with limit breaks (See Abusing Duel). Always keep the item person ready with a Holy War. All in all, if you are ready, this battle won't be too hard.