Ozma

Attacks  

Ozma has a variety of devastating attacks at its disposal, including one that has the ability to one-hit your entire party. 
 
Death: If the spell hits its target is instantly killed, and Ozma's hit percentage with it is higher than average. 
 
Lv5 Death: Any member of your party whose level is a multiple of five is killed instantly. 
 
Holy: Similar to Eiko's Holy spell. Inflicts Holy damage on a single target. 
 
Lv4 Holy: All members of your party whose levels are a multiple of four take Holy damage. 
 
Star Flare: Does non-elemental damage to all party members based on their levels; the higher a character's level, the more it hurts. 
 
Curaga: Ozma starts casting this on itself when you've done significant damage. 
 
Mini: A single target is afflicted with the Mini status ailment, causing a substantial decrease in both strength and defense. 
 
Flare: Similar to Vivi's Flare spell, except it hits harder. Non-elemental damage to a single target. 
 
Meteor: Does random damage to all party members. Sometimes it wipes out your entire party instantly, doing 9999 damage to everyone. Other times it will just knock off a few hundred HP. Capable of hitting some characters while missing others. 
 
MP Absorb: In the unlikely event Ozma runs low on MP, it will drain some from a party member. 
 
Esuna: Should you manage to inflict a status effect on Ozma, it will remove it using Esuna.  
 
Berserk: Used as a counterattack. When one of your party members uses a physical attack against Ozma, it will counter with Berserk.  

Doomsday: Deals Shadow damage to every character on screen, including Ozma. However, Ozma absorbs Shadow damage unless you complete the Friendly Monsters sidequest mentioned below. This spell will heal Ozma if you haven't done the quest and hurt it if you did. 
 
Curse: The most infamous of Ozma's attacks by far. Inflicts every status ailment in the book on all your party members and also deals significant damage. The amount of HP it takes off is somewhat random, but even the low end hurts a lot. If you see this attack more than twice in the battle you're probably out of luck.  
 

Preparation  

First off, this is a highly luck-based fight no matter how well you prepare. If the AI decides it likes Curse that day, you will lose. Period. And even if things are going well, there's always the chance Ozma casts Meteor and wipes out your party instantly. Don't expect to win this fight the first time, or even the tenth time. The good new is Ozma only has 55,535 HP. Most of your attacks should be doing 9999 damage or close to it, so it could be a quick fight if things go your way.  
 
There are a number things you can do to improve your chances against this tough boss, with the most important being the Friendly Monsters sidequest. In certain locations on the world map you may encounter friendly versions of normally hostile monsters. You'll know when you've encountered one because instead of the regular battle music a peaceful tune will play. The monster will ask for a specific gem. Go into the item menu and use the requested stone on the monster. The encounter will end and you'll receive large amounts of AP, much more than a typical battle, and other rewards. Attacking a friendly monster will cause it to flee, making the quest impossible to finish.
 

Monster	Location	Request	Spoils
Brown Mu	Plains and forests between the Ice Cavern and Dali	1 Ore	10 AP, 1 Potion
White Ghost	Plains around Treno	1 Ore	10 AP, 1 Hi-Potion
Colorful Ladybug	Forest around Black Mage Village	2 Ores	20 AP, Ether
Green Yeti	The larger forest outside Madain Sari	2 Ores	20 AP, Elixir
Green Nymph	Forest near the Iifa Tree	3 Ores	30 AP, Emerald
Purple Jabberwock	Forest east of Oeilvert	Emerald	40 AP, Moonstone
Green Feather Circle	On the Lost Continent's ice field, near the chocobo tracks	Moonstone	30 AP, Lapis Lazuli
Rainbow Garuda	Eastern forest near the rope exit of Gizamaluke's Grotto	Lapis Lazuli	40 AP, Diamond
Yan	Forest on Vile Island, the landmass southwest of the Iifa Tree	Diamond	50 AP, Rosetta Ring

 
The Yan must be done last, but the others you can go after in whatever order you want. However, it makes sense to do them in the sequence listed because the spoils provide you the gem requested by the next monster. 
 
Doing this sidequest will help you against Ozma in several ways: 
 

• The AP you get from the monsters will allow you to learn any abilities you want to use in the fight much faster.
• After receiving the Diamond the Yan will inform the player that the "the round guy," Ozma, can now be reached with physical attacks.
• Although the Yan never states it, finishing the quest also removes Ozma's ability to absorb Shadow damage.

 
That last point is the important one. If you outfit your party with Shadow absorbing or nullifying equipment, whenever Ozma casts Doomsday it will do massive damage only to itself. Your party will be either unharmed or healed. Ninja Gear, Demon's Mail, and Pumice Pieces absorb Shadow, and Egoist's Armlets neutralize it. Equipping each party member with one of those four items will help in the battle, whether you did the Friendly Monsters sidequest or not. 
 
Abilities 
Every member of your party should have the Antibody and Clear Headed abilities equipped. They make Curse a little less painful. Any character that you think you might want to use physical attacks should have Bright Eyes, because Curse causes Darkness as well. If you do plan on using physical attacks against Ozma, which isn't necessarily advised, Auto-Reflect will keep your characters safe from its Berserk counter. You can also use MP Attack and Bird Killer to boost physical attack damage dealt to Ozma. Loudmouth is an essential ability for your mages. Wasting turns curing Silence is not something you can afford to do. Abilities that increase the total MP of your mages and reduce the MP cost per spell are also very useful. Every character should have Auto-Regen, and HP X% abilities should be used if available. 
 

Strategy  

One important thing to know going into the battle is how Ozma's hidden ATB meter works. Whenever you issue a command targeting Ozma while Ozma is not in the process of casting a spell, its ATB meter fills instantly and it will act before your characters do. This ability to basically take extra turns is one reason this boss is so difficult. Try to input all your offensive commands while Ozma is in the middle of casting a spell, before the damage and/or healing numbers appear on the screen. This way Ozma will get as few turns as possible. 
 
Try to have one party member whose level is a multiple of four. This will entice Ozma to use Lv4 Holy, one of its weaker attacks. Any turn you don't see Meteor or Curse is a good one. 
 
Zidane's Thievery, Freya's Dragon Crest, and Quina's Frog Drop can all do 9999 damage per use if you power them up enough. Steiner's Shock Sword Art hits for 9999 right out of the gate. Having at least two of these high damage-dealing skills at your disposal will definitely make the fight easier. Assuming you did the Friendly Monsters sidequest and outfitted your party in Shadow-absorbing gear, Vivi's Doomsday spell is another skill that can be very useful. Whenever he casts it Ozma will take damage and your characters will be healed.