Disc 1
Quetzacotl
A Thunder-Elemental Guardian Force that damages all enemies. This attack will work on all bosses unless they absorb this magic or have very high defenses.
Obtain by: Looking in the Study panel tutorial or given to you by quistis.
Shiva
An Ice- Elemental Guardian Force that damages all enemies. This attack also works on all bosses unless they absorb the magic or have high defenses. Shiva has been in every FF to grace our Playstations up to 10.
Obtain by: Looking in the Study panel tutorial or given to you by Quistis.
Ifrit
A Fire-Elemental Guardian Force that damages all enemies with a fire attack. Another character that has been in the previous FFs up to 10.
Obtain by: Defeating him in the Fire Cavern
Siren
A non-elemental Guardian Force, that will cast the status effect "Silence" on one or all enemies. This attack however, does not work on all enemies (bosses in particular). This attack can also have it's advantages though, if a monster uses only magic attacks.
Obtain by: Drawing from Elvoret(Dollet tower) or from Tri-Point at Ultemecia's Castle
Brothers
An Earth element. These two brothers join together damaging all enemies/bosses that are on the ground. If the creature is a fly creature, it will miss, because of course this is an Earth element, and the creature of course is not touching the ground.
Obtain by: Defeating them in the Tomb of the Unknown King
Diablos
A non-elemental Guardian Force, that was living in a Magic Lamp. He can become very powerful, but there are a lot of enemies that are immune to this attack (Bosses and monsters).
Obtain by: Using the magic lamp and defeating him.
TIP:If your having trouble beating him try junctioning 100 Blinds to status attack to blind, and have Selphie in your party so after he cast Gravija you can use full cure.
Carbuncle
Another non-elemental Guardian Force. Carbuncle will cast "Reflect" on your party. When using this make sure someone in your party is Junctioned with "Item" so you can still heal your party.
Obtain by: Drawing from Iguions (Presidential Residence in Deling City) or Krysta at Ultemecia's Castle
Disc 2
Leviathan
A water-elemental Guardian Force. Leviathan's attack is strong and will hit all enemies. This attack works unless they absorb water based attacks or have high defenses. Leviathan has been some previous FFs.
Obtain by: Drawing from NORG (once his pods are broken) or from Trauma at Ultemecia's Castle.
Pandemona
A wind-elemental Guardian Force. There are a lot of enemies with weaknesses to Wind magic (fly type especially), and there's not much to choose from when it comes to Wind based magic, and you can get to quite a high lvel using boost.
Obtain by: Drawing from Fujin (at Balamb) and Red Giant at Ultemecia's Castle.
Cerberus
Cerberus' attack well isn't really an attack, it will cast Double and Triple on all your party members. VERY handy, so make sure your compatibility with hi is high so its a quick summon.
Obtain by: Defeating him at Galbadia garden (invasion)
Alexander
Alexander's attack is elemental Holy based. It's extremely effective against the undead or creatures affected with Zombie. Can become quite a strong attack, an gives you adecent amount of time to boost.
Obtain by: Drawing from Edea at the end of disc 2 and Catoblepas at Ultemecia's Castle.
Disc 3 & 4
Doomtrain
A poison-elemental GF. This GF is a ghost train. This train runs through space and into the enemy casting poison and other abnormal status' on the enemy.
Obtain by: Getting 6 Malboro Tenticles, 6 Remedy Plus and 6 Steel Pipes and use the Solomons Ring (found at Tears point)
Bahamut
A continuation with the same attack known as Mega Flare (From Final Fantasy VII). This non-elemental GF isn't quite powerful with it's attack, however, the attack animation is long and enables you to boost the GF close to the 250 maximum.
Obtain by: Defeating Bahamut in the Deep Sea Research Lab.
Cactuar
This GF is giant Cactuar. It grew up and lived long to become very large in size.
Obtain by: Defeating Jumbo Cactuar on Cactuar Island (you will see him pop up, it's a small island near the main cactuar island)
Tonberry King
Ah the infamous tonberry whom i remember watching my brother fight many in FFVII. Well now he can be your ally as well as your enemy.
Obtain by: Defeating 20 Tonberrys and defeating the Tonberry King you encounter after. (Same place you get Odin)
Eden
Eden, has the most powerful attack taking at LEAST 11,000 points off an enemy, if it is built. Eden also has a weird ability known as Devour. This Devour skill let's you EAT the enemy.
Obtain by: Drawing from Ultima Weapon In the Research Facility you get Bahamut