FOR THE ON MILLIONTH TIME!! LEVEL UP!!!
grrr. guess I have to tell ya anyways.
Have your players overdrives full. then go into battle with the boss. when you first get in, have yuna summon a weak aeon, and then have the aeon use shield. the dragon will then cast a beam sort of attack which causes, poison, curse, and darkness.
After your aeon gets hit by the attack, dismiss it and have your characters use their overdrives on its ass. Once it gets low on HP, it will use curaga to heal itself. At that time, use reflect on it, so it cant heal itself. You may also want to study the pattern of its attacks. I think it casts the beam like attack every few turns. So try and cast an aeon right before he does and have the aeon use shield.
Thats about all you can do. But make sure you stock up on items like holy waters, remedy`s, and some other things you may need. Since there are absolutely no places to buy things for the next 2 bosses. So if you havent, you may need to go back to mount gagazet and buy things from oaka`s brother.