Guardian Forces

Name: Shiva Shiva
Attack: Diamond Dust
Location: Balamb Garden Terminal
Strong against fire, this hindu god gives you some handy Elem Junctions and the death clock, Doom.
Name: Quezacotl Quezacotl
Attack: Thunder Storm
Location: Balamb Garden Terminal
This Aztec god gives you an edge over mechanical and water enemies. Card turns an enemy into a card, and Card Mod turns cards into great stocking stuffers.
Name: Ifrit Ifrit
Attack: Hell Fire
Location: Fire Cavern (near Balamb)
Summoning this demon launches a rather large fireball type thingy at your foes. Strength junctions and Ammo-RF are useful.
Name: Siren Siren
Attack: Silent Voice
Location: Draw from Elvoret, Dollet Communications Tower
Siren deals some non-elemental damage while inflicting your opponents with silence. Treatment and Stat junctions are great, and Move-Find points out some valuable draw/save points.
Name: Diablos Diablos
Attack: Dark Messenger
Location: Use 'Magical Lamp' from Cid
Make sure you get the Magical Lamp from the headmaster before you head out to Timber. This devil's power is proportional to your enemies. Against stronger enemies, Diablos deals out 9999hp of damage. Mug lets you steal valuable items from your enemies, and Enc-Half/None reduce battles.
Name: Brothers Brothers
Attack: Brotherly Love
Location: Tomb of the Unknown King
Sacred and Minotaur, earth, are weak against flying monsters. HP+ abilities can bring up your HP quite a bit.
Name: Carbuncle Carbuncle
Attack: Ruby Light
Location: Draw from Iguion, Lizard beasts that attack Rinoa in Deling
Carbuncle casts reflect on all party members. Auto-Reflect and Counter abilities return damage to opponents.
Name: Leviathan Leviathan
Attack: Tsunami
Location: Draw from NORG, Balamb Garden
Water damage with plenty of boosting time. Recovery and auto-potion are excellent healing ablities.
Name: Pandemona Pandemona
Attack: Tornado Zone
Location: Draw from Fujin in Balamb
This freakish looking thing gives tremendous gusting power, Spd junctions and Absob ability.
Name: Cerberus Cerberus
Attack: Counter Rockets
Location: Defeat him, Galbadia Garden
Summoning Cerberus casts Double and Triple on all party members.
Name: Alexander Alexander
Attack: Holy Judgement
Location: Draw from Edea, Galbadia Garden
Holy damage. Revive, Med Data are great for recovery, and Elem-Defx4 can make you strong against any element.
Name: Doomtrain Doomtrain
Attack: Runaway Train
Location: Use Soloman's Ring with these items:
Soloman's Ring: Tear's Point (if pandora present, walk under it), 6 Remedy+: MedLevUp remedies, 6 steel pipes: mug Wendigos, 6 Malboro Tentacles: Mug/Win from malboro.
Name: Cactuar Cactuar
Attack: 1000 Needles
Location: Defeat Jumbo Cactuar on the desert Cactuar Island
Eva/Luck Junctions are offered only from Cactuar.
Name: Odin Odin
Attack: Zantesuken
Location: Centra Ruins
This GF, from Norse mythology, isn't Junctioned. Instead he randomly appears (more often with more luck) and kills off all enemies.
Name: Tonberry Tonberry
Attack: Chef's Knife
Location: Defeat about 20 Tonberrys (back-to-back without leaving) and the Tonberry King in Centra Ruins
Get after obtaining Odin. This will take a while, so plan to spend an afternoon fighting little green men. Tonberry gives you discounts and deals at shops.
Name: Bahamut Bahamut
Attack: Holy Judgement
Location: Deep Sea Reasearch Center
Make your way to the core and answer the questions. Fight the 2 ruby dragons, and choose the third invisible answer to question 3 to fight Bahamut.
Name: Eden Eden
Attack: Eternal Breath
Location: Draw from Ultima Weapon, Deep Sea Research Cente
The most powerful GF (after boosting). Massive Damage; breaks that pesky 9999 damage limit. You can get this GF after you have Bahamut. There are many hard battles there, and if you don't feel up to the challenge, you can wait and draw Eden from Tiamat at Ultimecia's Castle (Clock Tower) on Disc 4.
Name: Gilgamesh Gilgamesh
Attack: Various
Location: Obtain Odin, Defeat Seifer, Disc 3 End.
Same deal as Odin, but one of four attacks—Zantensuken or 3 others, dealing little or heavy damage.
Name: Phoenix Phoenix
Attack: Rebirth Flame
Location: Use Phoenix Pinion in Battle.
Phoenix is not junctioned or obtained, but can be summoned in battle to revive any fallen members, and deal some Fire damage to your opponents. After using a Phoenix Pinion, this GF may return to raise a fallen member.
Name: Boko Boko
Attack: Choco Flare
Location: Use Gyshal Greens in battle.
Gyshal greens can be cought in any Chocobo Forest. Boko attacks your chosen target with Fire.
Name: Moomba Moomba
Attack: MoombaMoomba
Location: Use Friendship in battle.
The Friendship item is only available from the PocketStation device. This device, unfortunately, was never released in North America. The good news for some is that the PC version of the game can be equipped with a Chocobo World PocketStation emulator.
Name: MiniMog MiniMog
Attack: Moogle Dance
Location: Mog's Amulet.
The Mog's Amulet can be obtained from the PoketStation as well. (see above) It teaches a command that calls MiniMog. Moogle Dance heals your entire party (for a price).