The way I killed it was by using the ALL LUCKY SEVEN ...very easy. All I did was go into battle in some area where the enemy is weak and let it hit me until I get the last two digits of my HP to be 77 (asuming your HP is lower than 7777 when the enemy hits you) and then I just used potions and stuff to get it up to 7777!!! After this I changed that character with HP of 7777 so I could use it for the weapons battle and replaced it with another character to do the same thing. Do the other two charcters besides Cloud (You can't change Cloud) first and then try to do it for Cloud after reserving the other two characters for the weapon. Once you got Cloud ready aswell then put all the characters with HP 7777 and you'll win for sure. Hey it might take a while to get the last two digits as 77 but it works ...well for me it did. A good place for doing this I think would be near Midgar.

I don't know much but has anyone tried this before? I think lots of people have and know about this.