Omega Weapon is the toughest monster to defeat in Final Fantasy VIII, tougher than the final boss, and much much tougher than Ultima Weapon. To actually battle Omega Weapon, there are some things you must do. When you are in Ultimecia's Castle, save your game and take your best party, the party with which you are going to battle Omega Weapon, into the courtyard (where there is the fountain, and a door leading to the church). Use the party switch point and switch to your other party. There is a room beyond the Art Gallery which has a rope in it. Take your second party (who will not be fighting Omega weapon) into this room and pull the rope. A bell will then start to ring and you have a few seconds to quickly use the switch point to get to your first party. Take the first party into the church and you will see that the black hole normally present there is gone, and in it's place is Omega Weapon. Run up to him, pressing the X button, just run into him until the battle starts.

Before taking on the challenge, remember some things:
1. He has 1,500,000 (1 and a half million) HP.
2. He absorbs all elements.
3. No Status will work on him, except Vit=0.

His attacks are the following:
1. Lv. 5 Death - this is lethal because if you're fighting Omega Weapon, you will have to have your characters at Lv. 100 to be at 9999HP without wasting ability slots on HP+??% abilities. It is better to use these slots to raise your Spr, Vit and Spd. Junction 100 Death spells to each of your party's Stat-Def-J slot.
2. Gravija - this removes 75% of each of your party members' HP (bringing them down to 2500HP if they had 9999HP when the Gravija was used). It also causes Curse. Use Full-Cure, Curagas and Esunas to heal the damage.
3. Light Pillar - just like Ultima Weapon, this attack will remove 9999HP from one party member. This is normally triggered as a counter attack if you use Physical attacks on Omega Weapon. You can only receive less than 9999 damage if your Vit stat is over 200. (Junction Meltdowns and Vit+??% abilities)
4. Terra Break - this is extremely lethal... you really cannot expect any of your party to survive this if you are caught with all your party not invincible (Don't use Holy Wars or this situation is very possible, click here for more information about Heroes and Holy Wars.
5. Medigo Flame - another undefendable attack, this one can really hurt your party, if not kill them completely. Again, Heroes are a must.

Don't worry though, as long as you have the following, Omega Weapon is possible to kill. It's a great feeling when you do, so give it a try! You will need:
1. Heroes - refine that Laguna Card
2. Megalixirs and Elixirs - refine the Angelo card and the Bahamut Card
3. Squall in your party with the LionHeart - absolutely necessary
4. Aura spells
5. Ultima spells
6. Meteor spells
7. ...or of course you can take the easy way out and kill him using Selphie's 'The End' Limit Break... but where's the satisfaction in that? Don't give in to temptation and give up on Omega weapon and just use 'The End'... he really is not impossible to kill!!!
8. The party you take MUST have their ultimate weapons

What commands should you have?
1. Restore is a must... it restores all the HP of one party member, GF Leviathan has this. Equip it! (of course, only one person can have this)
2. Item - this is necessary for using Heroes
3. GF - don't bother with this on a person who has only elemental GFs - Omega Weapon absorbs all elements. The only GFs you can use are the one that help your party and Cactuar and Eden. I think you can also use Doomtrain and Bahamut, though I'm not totally sure.
4. Magic - necessary for using curative spells and non-elemental spells such as Ultima and Meteor. Also important for casting Meltdowns.
5. Draw - if you wish, although Omega Weapon can turn nasty if you Draw from him!

Now for the actual battle! Take the usual preparatory steps, ie:
1. Cast Triple on all your party
2. Cast Regen, Protect, Haste, Aura on all your party
3. Cast a Hero on one person
4. In the next round cast two other Heros on your remaining non-invincible party members. In this way it is very very rare that you will be caught with a party completely non-invincible. Remember that if a party member is Invincible, using Aura on him will have no effect, as will all other Magic. Keep that in mind. When a party member loses Invincibility, cast Aura, then use a Hero on them.
5. Cast Meltdowns on Omega Weapon until he turns a nice shade of pink/purple.
6. Start using Limit Breaks! The best ones to use are: LionHeart (Squall), ShockWave Pulsar (Quistis) and Zell's Limit Break is also very effective (just keep repeating basic moves again and again till you only have about 2 seconds left, then do a combo that will lead to a finishing move). Selphie's Limit Break is only really good for Full-Cure, Rinoa's is only good for Invincible Moon and Angelo Revive and Angelo Restore, Irvine's is pretty good, especially the Demolition Ammo, but Squall's Quistis' and Zell's are better... so it looks like your party is complete!
7. This is really all there is to it. Aura, Hero, Limit Break. Aura, Hero, Limit Break. If you have a party member invincible but not under the spell of Aura, use GFs like Cactuar and Eden, or just use Physical Attacks... Omega Weapon's Light Pillar attack can't hurt you now! Keep it up and eventually you'll beat Omega Weapon and be able to breath the biggest sigh of relief ever! Plus, it feels darn good!!!
8. If you don't manage to beat him, don't give up, and don't feel too bad, he IS extremely tough... hey at least you tried!