Before challenging Ozma, there are a few things you need to do beforehand to prepare yourself for the battle to come.

You will need to decide whos going to be in your team, we would suggest Zidane, Steiner, Quina and Dagger. This way you have a good balance of magic and physcial attacks. This is because you can use Steiner and Zidane to use their normal attacks, which are powerful normally, but also if you are able to get a trance with either of them, you are able to cause a maximum of 9999 HP Damage. Quina is able to use an assortment of magic, black and white as well as Frog Drop, and Dagger can be used to Summon as well as heal and restore HP.

Having Quina in your party means that you will be able to use the powerful Frog Drop ability. The move becomes more powerful as you catch more frogs so travel around Gaia and visit all the Qu's Marshes and catch as many as you can, the more you catch the more damage you will do. Be sure to leave at least one Male and Female Adult in each pond so that they will breed quicker. There is a rule you can use to work out how much damage Frog Drop will cause, if you divide 10,000 by your status level, you can determine how many frogs you need to cause 10,000 HP of damage. The higher your status level, the fewer frogs you need.

Be sure to get your status levels up. There are a number of ways in which you can do this, one is by fighting the Grand Dragons that inhabit the entrance to Daguerro. The other, although more life threatening is better as you will gain much more EXP, the Yan inhabit the island off the coast of the Outer Continent, near to the Lifa Tree. This island is only accessible with the Invincible or a Gold Chocobo, due to it having no landing area for the Hilda Garde 3. The Yan have just under 20,000 HP and have an array of attacks that include: Snort, Aera, Comet, Float and Virus Powder. Snort is the most lethal and will remove one character from the battle screen, Aera will cause a couple of hundred damage, Comet has a 50% hit chance so it won't always do damage, Virus Powder also has a 50% hit chance and if one of your party is inflicted with it, they will not recieve EXP unless you remove it. Try using summoning Odin as he may kill them in one swoop for you, alternatively use Ark and if Steiner has Excalibur you can use Climhazard. Both attacks are sure to deal 9999 HP each time. Increase everyones level to around 80, this way you have a increased chance of winning.

Ok, so have enough frogs, whose in your team and you have raised their status levels. Now before you leave Vile Island, keep fighting untill your teams trance meters are almost full. This will enable you to use an assortment of Trance moves on Ozma and will greatly increase the chances of you winning against him.

Ok, below is a list of how we had our party equipped when fighting Ozma. You do not have to follow this, but its a good set up, and you should know all the abilities needed by now. Those items with a '*' in front of them can be obtained through finding all the Chocographs.

Zidane:
Equipment: Ultima Weapon, Thief Hat, Egoist's Armlet, Ninja Gear, Ribbon.
Abilities:Auto Haste, Auto Regen, Auto Life, HP +20%, Accuracy +, Distract, Gamble Defence, Antibody, Clear Headed

Steiner:
Equipment: *Ragnarok, Diamond Helm, Gauntlets, *Demon's Mail, Protect Ring.
Abilities: Auto Haste, Auto Regen, Auto Life, HP +10%, HP +20%, Accuracy +, Chemist, Antibody, Clear Headed.

Quina:
Equipment: Gastro Fork, Golden Hairpin, Dragon Wrist, Demon's Vest, Protect Ring.
Abilities: Auto Haste, Auto Regen, Auto Life, Add Status, Gamble Defence, High Tide, Anti Body, Clear Headed.

Dagger:
Equipment: *Whale Whisker, Golden Skullcap, Dragon Wrist, Robe of Lords, Rossetta Ring.
Abilites: Auto Haste, Auto Regen, Auto Life, MP +20%, Healer, Reflect-Null, Antibody, Clear Headed.