Ultima Weapon attacks with Crush, which can instantly kill a character; Laser Barrage, which does minor damage to the party; plus Flare and Bio, which do heavy damage. When its HP falls to a certain point, Ultima Weapon will take a turn to cast Haste, Shell, and Protect on itself. On its next turn the player will get a warning that Ultima Weapon is charging up a Meteor spell. The turn after, Ultima Weapon uses Meteor to do massive damage to the party.
After Meteor is cast, Ultima Weapon changes its attack patterns. It will use Tornado to inflict critical status on a party member; Magic Buster, which damages a character's MP; and Laser, which is virtually an instant kill. It will also use physical attacks during both phases, which do high damage.
It is not recommended to face the Ultima Weapon until the party is at least Level 55 during the Waxing Moon Phase. A Black Mage should wear the Rapid Ring V2 to lower their casting time, while a White Mage should equip the Twin Stars to halve their MP usage.
The party should begin the battle by casting Slow or using a Spider's Silk on the Ultima Weapon. During the fight, a White Mage should use Arise whenever a character is hit with Crush, otherwise they should cast Curaga or Curaja nearly every turn. Should the White Mage fall, someone should quickly revive them using a Phoenix Down or Raise. Abilities such as Heal Pill Ninjutsu are useful to speed up the healing. One should also caste Haste on the party. X-Potions can also be used for quick healing.
Physical fighters should use abilities such as Jump or attack with weapons like Excalibur or Ragnarok. It is also effective to use Bands that can potentially break the damage cap of 9,999, such as Sky Grinder. A Black Mage's best spell to use on the Ultima Weapon is Flare with the Limit Ring. Meteor is also good, but it will take longer to cast.
When Ultima Weapon strikes with Meteor, fallen party members should be revived and promptly healed; casting Blink can protect the party from subsequent attacks. After his attack pattern changes, a White Mage must then heal twice as often, as Ultima Weapon uses attacks like Tornado. The party should cast Slow every time Ultima Weapon casts Haste on itself. Notice Ultima Weapon will now use Meteor randomly.
Characters must be prepared with items like Dry Ethers to restore their MP, especially after being hit with Magic Buster. If the player has Porom in their party with Dualcast, she will be a better alternative than Rosa, as she can use two White Magic spells in one turn.
Ultima means "the last" in Latin and many Latin-based languages. In the Spanish versions of many Final Fantasy games, it is written as "Artema," a close transliteration of the Japanese katakana.