Instructions
Death Trick
Put Fang, Lightning and Vanille on your team if you prefer attack over defense. As soon as the battle starts, summon any creature. The creature knocks the Adamantoise down.
Cast Haste to speed the party up, and then switch to the Infiltration paradigm. Cast the Death spell repeatedly. If it hits, the monster dies in one hit. If the move doesn't hit, Adamantoise gets back up and is likely to wipe out your team.
Put Vanille, Snow and Fang on your team if you favor defensive strategy. Switch to the Premeditation paradigm and begin casting Death. Have Fang cast Haste on your party.
Switch to the Overcaution paradigm to enter a defensive state. Keep casting Death. Heal by switching to the Combat Clinic paradigm. If Death hits, Adamantoise is defeated.
Second Strategy
Place Fang, Vanille and Lightning on your team. Switch to the Recupperance paradigm immediately when the fight starts, and then cast the Bravera and Haste spells on Fang.
Cast Faithra and Protectra on Vanille and Lightning. Have Lightning cast Protect on Fang and then caste Haste on the party.
Switch to the Thaumaturgy paradigm and begin attacking the Adamantoise's legs. When the leg gets to 300 percent damage, switch to the Discretion paradigm and use the Highwind move on it.
Switch to the Espionage paradigm when both of the Adamantoise's two legs are destroyed. Cast Faithra and Bravera on the party. Cast Deshell, Deprotect and Imperil on the Adamantoise.
Go to the Tri-Disaster paradigm and have all party members attack. When the Adamantoise's damage meter reaches 900 percent, switch to the Aggression paradigm. Continue attacking, and then use the Highwind move to finish Adamantoise off.