As Omega is very fast, i suggest that you configure the Active Time Bar (ATB) to wait, and battle speed to the slowest.

I'd advise that you let Squall, Irwin, and Zell fight this beast. Coz they have awesome Limit Breaks. Let one of them equip Leviathan's Recovery and let the other two characters equip Item, Magic, and G.F. Let me warn you that Omega will cast Death, so junction Death to Status

Defend. Do not juction Holy to Element Attack.

Here are the the moves that Omega will use:

1. Death

2. Meteor

3. HP to 1 on all characters (9998 damage to all)

4. Demi (HP reduced to 1/4)

5. Mega Death (you will know when you see it)

6. Demi

7. 9999 damage to a single character.

And here's the strategy:

Speed is everything in this battle. So junction Haste to Speed, equip Cerebrus' Haste as well. Make sure that all the characters have 9999 HP coz Omega has got a nasty 9998 damage to all attack.

Omega is definitely gonna cast Death for his first move. So you have nothing to worry about. Summon Cerebrus, so that you can cast spells yourselves 3x consecutively. It is advisable that the character that is equipped with Cerebrus has a high 'affection rating' with it. ('affection rating' rates the speed of a Guardian Force when it is summoned by a particular character)

Cast Aura so that you could do limit breaks without having your HP to critical. If you still can't get it, press Triangle multiple times until you do. Don't bother summoning Guardian Forces to inflict damage as Omega won't feel a thing. The only Guardian Force worth summoning is Eden which damage incurred exceeds 4 digits, i.e. more than 9999. At Level 50, Eden does 30,000 t0 40,000 damage!

Then Omega will cast Meteor, fully heal your characters coz he will inflict a 9998 damage to all soon after. After your characters HP has been reduced to 1, use you limit breaks for your advantage. Limit breaks performed are better when HP is critical. (E.g. Irwin can shoot up to 8 times when his HP is critical but only 3 to 4 time when HP is full using Aura.) Do not bother to heal your characters as the next attack followed is Demi (HP reduced to 1/4)your HP is already 1, it will stay that way. Then, fully heal yourself and summon GFs with high HPs, or you can use 'Hero Drink' (invincibility) in your

inventory if u have it. Omega is gonna cast Mega Death that is devastating.

If you have summoned Gfs, they will probably die, when they do, your character continues to sustain damage from the attack! Do not bother to heal, as the next attack would be again Demi. Use the Deperation Moves to your advantage. Next, Omega will unleash a 9999 damage on a single character.

After that, Omega would unleash random spell attacks, but never the same spell consecutively, so good luck!