Omega Mark XII
About 900 000 HP
Resistant to Libra
Omega is located at the top floor of Great Crystal (look in "Great Crystal II" part for exact place). He is there all the time, but he is asleep. He wakes when you get a task to defeat Yiazmat. The only reason of that fight is to have him in Bestiary and getting Omega Badge.
As you probably noticed I mentioned only Protect, because he doesn't have more attacks, except for the normal ones, and actually, he uses it very rarely. He doesn't need other attacks at all, because he can kill your character with one shot, and your own attacks wounds you also. Not funny, eh? Not funny at all.
To that fight you need Bubble Belts. And use the same strategy like in Hell Wyrm's case, I mean Decoy and Reverse, but don't use Berserk. You need to have your characters with clear mind. Omega has less than one million HP, but it doesn't mean that he is easier to defeat. In that fight despite all appearances you will spend more time on healing yourself than on attacking him. Moreover try to cure without delay, and don't run, because Omega will use it and start to heal himself at a great speed.
I've got one more bad news - he becomes stronger at the end of the fight and his defense increases.