My emmy method was really really involved, but worked...
I used Vincent, Cid, and Cloud (duh)
1st, I got all the ultimate weapons and level 4 limit breaks. Then, I built up even more BP in the battle arena until I had bought 99 Starduts (which cast comet-2, i think).
2nd I went to north crater and fought Blue Dragons until i had 99 megalixers

These two steps are a hell of a lot easier if you use the item cloning trick, which i didn't know about at the time.

3rd, i equipped nil materia, Cid had KotR and HP Plus, Vincent had Mime and HP Plus, Cloud had Hp Plus underwater, and W-item.
4th I went out, and beat the crap out of my characters to get thier HP to below 154, and equipped a cat's bell, when their HP hit 154, i would un-equip it and get into an easy battle and cast demi-2 on that character, bringing his HP to 77, i would have used cat's bell, but it only goes to even numbers. Then, hi-potions and potions would bring that person up to 7777. I did this with all 3 characters.
When the battle finally started, i did nearly 500,000 damage from the lucky 7s, then I cast KotR and mimed it. After that, every single character would use a megalixer on thier turn, except cloud, who would use megalixer and stardust. After all the "eyes" were dead, I used omnislash and killed that big green mofo.


Ruby was easy, cloud had Final Attack-Phoenix along with Hades and a coulpe other things, and Vincent had master magic, Cid had Master Summon and some other stuff. I started off with Vincent and Cid dead. Then, i just waited and after cloud died and phoenix resurrected all 3 characters, I cast Hades, then KotR, and Bahamut Zero and other stong stuff. It was pretty easy.