Omega Weapon is located in Ultimecia’s Castle, Well preparin for this is pretty easy, make sure you get Gilgamesh card from the CC King and then refine it into 10 Holy Wars. Make sure you have Deaths junctioned on your characters status Defense. Make sure you have Doomtrain GF or alot of Meltdowns stocked. To get him to appear take your main party to the switch point by the fountain and switch to the other party. Take that party to the door right of the main hall, inside the room is a rope that rings the bell on the ceiling. When you ring it, quickly switch to the other party and run through the door to fight Omega. Before ringing the bell set up your junctions, abilities, magic, and items so you can heal and revive in the fight quickly. Start out by summoning Cereberus GF, and Doomtrain GF, Doomtrain will make the fight much easier. If you have the chance you can stock tons of stocks, for the Last boss, I actually just fight Omega Weapon then restart the game so, I can have more fun by fighting him again >_

Well I then start using Zell's limit break to damage him, I also used Holy Wars, and I then use Rinoa's Limit break, somehow I keep getting "ANGELO RECOVER" and "INVINCIBLE MOON" I have a alot of luck sooo. I basicly just keep attacking w/ Zell's Limit break, You should use the combo of "Punch Rush" and "Booya" over and over again. Then you should take advantage of Squall's limit break, Lionhearts rare, but if your Squall is really good, it should do alot of damage. When Doomtrain is over, summon him again to replay efects. You really don't need to summon that many GF's. Once you beat him you get "Proof of Omega" in your Tutorial.