Gigantuar is found in the Archylte Steppe by examining blue cactuar statues, most of which appear once Faeryl is defeated and when the weather is right. One of the stones is surrounded by a group of growing cacti on the east side of the gorge in the Stonestump Wasteland in any weather right from the beginning. The other two statues are in the Clearwater Marshes: one is in the northeast during sunny weather, and the other is in the center during rainy weather. Both statues require Moogle Hunt to find.
The player can get to the Clearwater Marshes by teleporting from the yellow cactuar statue, which appears in cloudy weather. One can also simply jump across if they have unlocked the correct Fragment Skill from Serendipity, or gotten the chocobo from the nomad camp (only after finding all five of the cactuar waystones, thus access to the western part of the map is needed anyway).
A defensive strategy can be effective for a low level party.
For a defensive strategy, Serah must have unlocked the Saboteur role and should know the abilities Poison and Deshell as well as having access to the Medic role, knowing Esuna and possibly knowing Curasa. Noel should have access to the Medic role and should know Esuna, Raise and Curasa. Having the Synergist role with Faith also helps.
A useful Feral Link is a Synergist that has the Faith ability, for example Microchu or Yakshini. Serah is probably the better of the two party leaders. The paradigms required are Salvation (MED/MED/MED), Perseverance (SAB/MED/MED) and Evened Odds (SAB/MED/SYN), which should be the active paradigm.
When the battle starts, the player should try to get Poison and Deshell on Gigantuar. Poison will typically take a long time to stick, and so the player should keep on using a manual command set of Deshell followed by Poisons. By the time Poison is on the enemy, Faith should have been cast on the party.
Once Poison is applied, depending on the player's level, the player may wish to go into a defensive type paradigm, such as Lifeguard or Salvation, to keep HP high. Even in this paradigm the player can deal damage via Feral Links. Alternatively, the player may want to go into an offensive paradigm to raise the chain gauge using Relentless Assault (RAV/COM/RAV) or Tri-disaster (RAV/RAV/RAV). Poison will probably have to be applied more than once to actually kill the Gigantuar. Once the enemy is staggered, Poison becomes easier to reapply, but if the player has low levels they may want to stay defensive.
As soon as a party member has been knocked out, the player should switch to Salvation to revive them with a Phoenix Down if possible due to higher healing potential. Eventually, Poison will fully wear out the Gigantuar's HP, but it is good to reapply it regularly to prevent it from running out.
This strategy can be used with parties of a higher level and so less healing is needed.
The player's Paradigm Pack should consist of a reliable Synergist that knows Faith (preferably Purple Chocobo or Yakshini), a Saboteur who knows Deshell and preferably Curse, and a choice between a Ravager or Medic depending on the party's HP. Noel should equip a Ribbon if possible, and Pain and Fog resistant accessories if not. The party's paradigms should be Countermeasure (SAB/SEN/SAB), Prudent Planning (SYN/SEN/SYN), Attrition (MED/SEN/SAB), Tri-Disaster (RAV/RAV/RAV), Mystic Tower (RAV/SEN/RAV) and Cerberus (COM/COM/COM).
Starting with Prudent Planning, the player should manually cast Veil on Noel and then the rest and wait until Faith is on the party. The party should then switch to Countermeasure to apply Curse and Deshell (and Poison if struggling). Once the debuffs are on, the party should switch to Mystic Tower to bring up the stagger gauge.
Once the stagger threshold is almost reached, the party should switch to Tri-disaster to stagger the enemy and bring up the chain gauge further and after a couple of turns use Cerberus to do damage. The last two steps should be repeated if the enemy is not yet dead, and the first two if buffs and debuffs run out. If healing is needed the Attrition paradigm can be used.
Gigantuar is a Synergist monster. It can get over 7000 HP, 500 Strength, and 1200 Magic only using Potent materials. Its true strength lies in its ability execution speed, which is only beaten by Sahagin Princes.
The Gigantuar crystal can be obtained three times; if the player does not have a crystal and fights a Gigantuar, they automatically obtain it. The Gigantuar can be leveled to 28 to obtain Auto-Protect, and then infused into another monster. The one big downside to this is the passive ability Fettered Magic, which reduces magic damage. It is a downside because it takes up an extra passive ability slot; it does not affect the Gigantuar's buffs nor its Feral Link. Infusing a Gigantuar into anything other than a Synergist or Sentinel would also gain the Fettered Magic's magic damage reduction. Gigantuar also learns Auto-Vigilance on the way to Auto-Protect, but this is arguably a detriment, as it is as useful as Auto-Protect and the like, but is ranked higher than them (Auto-Protect is Rank 7, Auto-Vigilance, Rank 8). Auto-Vigilance is impossible to get rid of without removing Auto-Protect, or the inefficient method of yellow-locking Auto-Protect and then adding it a third time to unlock it again.