you should have bahamut, cast him... have all your limit breaks set before you enter the boss battle... then Odin, Titan, Shiva, Ifrit, Rumah, etc... then use your limits (I had omnislash on the first CD) but use meteorain if you have it. I use Aeris for this battle simply because I make sure to have her Great Gospel Limit Break (Level 4 Limit) and cast it when you need it. If you don't ever use Aeris or you dont have her final limit I suggest you use Vincent/Barret and just beat him out as fast as possible and use a 3rd character ONLY to heal. You should have level 2 magic by now so use magic alot. Cloud should be your physical attacker though, heal all the time. Cast Cure with Aeris/healer person (since she should have lots of MP)... have ethers to heal