A small guide to all the GF in FFVIII
In FFVIII, GF are your lifeblood. Without them, your absolutely powerless. Since each quardian force has its own personality and unique traits, it's vital that you collect them all. Otherwise, you'll miss out on valuale skills (each GF has a one-of-a-kind ability). You'll also find it difficult to properly equip and balance your party. A smart adventurer isn't afraid to rely on his guardian forces and their powers. Doing anything else is just asking for failure. (GF are in the order you should recieve them)

Quezacotl

Usefulness rating: 5/5
Location: Balamb Garden, Squall's SeeD terminal
Attack: Thunder storm
Element: Thunder
Useful skills: Card command (turn your enemies into cards while their HP is low), card mod menu (transform your cards into useful/rare items), mid mag-RF menu (mid magic refine--turns 5 reg. magic into 1 more powerful one. ex: 5 Cures= 1 Cura) Overview: The Aztec thunder god puts the smack down on water-based and robotic foes, but his true power comes in card manipulation. Without his techniques, you'll have trouble obtaining the rare cards and items you need to thrive. In the game's early stages, mid mag-RF is invaluale.

Shiva

Usefulness rating: 5/5
Location: Balamb Garden, Squall's SeeD terminal
Attack: Diamond dust (Oh yea!)
Element: Ice
Useful skills: Doom command (Death--has countdown), Elem-Atk-J junction (elemental attack junction), Elem-Def-J junction (elemental defense junction)
Overview: The Hindu god of destruction is apparently moonlighting as an icy snow queen. Her Elem-Atk and Elem-Def junctions give characters an edge against elemental enemies. Fire-based enemies shiver at the thought of her diamond dust attack, but everyone fears her countdown to death called "Doom".

Ifrit

Usefulness rating: 4.5/5
Location: Fire Cavern
Attack: Hell fire
Element: Fire
Useful skills: Str-J junction (strength junction), Str+20/40% ability (Strength + 20 %, then 40%), mad rush command (casts bezerk on party members, haste, and protect), ammo-RF menu (ammo refine--get ammo from items)
Overview: This demonic hell-beast is a physical powerhouse. His strength junctions and percent increases beef up your blows, while his mad rush command instantly turns an ordinary party into a team of sped-up, protected, berserker killing machines. Ammo-RF becomes useful once Irvine joins your party (and when getting the lionheart)- without this skill, you'll be shooting blanks.

Siren

Usefulness rating: 3.5/5
Location: Draw from Elvoret, boss of Dollet assault scenario
Attack: Silent voice
Element: Nonelemental with silence status effect
Useful skills: Treatment command (cures all ailments--EXTREMELY useful), ST-Atk-J junction (Status attack junction), move-find party (finds hidden draw and save points)
Overview:Siren's forte is in quickly silencing a large group of foes. Treatment cures any status ailments and can be used even when your character is silenced--invaluable for opponents that mute an entire party at once. ST-Def-J junctions are helpful, but ST-Atk-J is invaluable: junction a large number of any status spell in this slot, and most physical strikes will be accompanied by a free casting of that spell that almost always connects--even against powerful enemies and bosses. Move-find reveals invisible save and draw points--often the only place to find the best spells.

Diablos

Usefulness rating: 3.5/5
Location: Use magical lamp received from Cid. To easily defeat Diablos, use his own power against him; Draw out demi and cast it on him to inflict massive damage. Polish him off with a few well-timed GF summons
Attack: Dark messenger
Element: Gravity-based attack
Useful skills: Darkside command, mug ability (steal items from enemies), enc-half (ecounter half), enc-none (ecounter none) party.
Overview: If Diablos appears to attack weakly, that's only because you're fighting weak enemies; his power is directly proportional to that of his foes. Darkside lets you sacrifice a tenth of a character's maximum hit points to deal a triply powerful blow; a worth sacrifice to finish off a weakened opponent. Mug is vital for finding rare items necessary for upgrading weapons and Quistis' blue magic. Enc-half and enc-none eliminate the headaches of random encounters (in most cases). If you really cannot beat Diablos after many tries, level up somewhere and try again! I do not use Diablos too often, but unless you love having those every-step random encounters, you really should get this GF.

Brothers

Usefulness rating: 2.5/5
Location: Tomb of the unknown king
Attack: Brotherly love
Element: Earth
Useful skills: Defend command, cover ability, HP+20/40/80% and HP bonus ability
Overview: First off, I would like to say that this is the GF I rarely use--maybe about 6 times in the game. They do not do that much damage, and most of the useful skills are found in other GF. I have to say, I can't really see a "one-of-a-kind" skill here, except that the HP abilities are really useful--4,000 HP to 9,999! ^^ I do believe you get the Minotaur and Sacred cards when you get them, and they are excellent cards. This team-up attack trounces ground-dwelling foes but is useless against flying opponents. Defend nearly eliminates damage recieved, while cover lets a character valiantly protect a weaker ally from an enemy's blows. The hit-point percentage increases can nearly double a character's hit points while the hit point bonus gives the character junctioned to the Brothers a hit point lagniappe with each gained level (around 30 HP).

Carbuncle

Usefulness rating: 3/5
Location: Draw from Iguion at end of disc 1
Attack: Ruby light
Element: N/A
Useful skills: Vit+20/40% ability (Vitality 20 and 40 %), auto-reflect ability, counter ability
Overview: (You'll find that you'll start using Carbuncle less and less as the game progresses because many of the enemies' attacks that do massive damage are not magic anymore -.-...more like "built-in")Ruby light casts reflect on each party member--a great opening defense against fierce magic users (great against Edea at the end of Disc 1). As a defensive GF, Carbuncle's strength is in increasing characters' constitution. His vitality percent increases can mean the difference between life and death. Auto-reflect is a double-edged sword with a permanent bounce-back, you can't cast helpful magic on your character, either (use items instead). Used properly, however, it's extremely helpful. Counter gives an attacked character a free counter-hit.

Leviathan

Usefulness rating: 4.5/5
Location: Draw from NORG in basement of Balamb Garden
Attack: Tsunami
Element: Water
Useful skills: Recovery command, Auto-potion ability
Overview: Learn the recovery skill immediately. This command refills a single character's HP--or does 9,999 damage to an undead creature (cast zombie if not); it's absolutely invaluable. Auto-potion lets a character automatically use a potion when hit, lessening the cumulative damage. It's best used in combination with Alexander's med data ability (makes more powerful medicine).

Pandemona

Usefulness rating: 3.5/5
Location: Draw from Fujin in Balamb Town
Attack: Tornado zone
Element: Wind
Useful skills: Spd-J junction (speed junction), Spd+20/40% ability (speed increase 20 and 40%), absorb command, initiative ability (VERY useful)
Overview: Pandemona's bizarre appearance harbors a strong, wind-based attack (if anyone can tell me basically where the eyes, ears, mouth are so I stop getting freaked out, it would be very much appreciated). Junction 100 hastes to your speed statistic to rocket fuel a character. The speed percentage increases are also useful. The absorb command drains hit points from an opponent and adds it to your own life meter. Initiative guarantees a character's ATB bar is full at the start of a battle.

Cereberus

Usefulness rating: 5/5
Location: Defeat Cereberus in Galbadia Garden lobby (really worth it!)
Attack: Counter rockets
Element: N/A
Useful skills: ST-Def-Jx2/4 junction (status defense junction x2 and 4), auto-haste ability, expendx2-1 ability (cast spell twice for price of 1)
Overview: Summoning Cereberus casts double and triple on all party members, effectively tripling your party's attacking and defensive power. He should be your first move in any boss battle. Auto-haste gives one character a permanent nitro infusion (starts at the beginning of the battle--cannot be disabled, does not go away after KO), while ST-Def-Jx4 defends you from 4 separate status effects. Expendx2-1 lets you casta spell 2 times for the price of 1.

Alexander

Usefulness rating: 5/5
Location: Draw from Edea at the end of disc 2
Attack: Holy judgement
Element: Holy
Useful skills: Revive command (EXTREMELY useful--you NEED this! Revives KO only, but completely restores character's HP), Elem-Defx4 ability (elemental defense x4), med data ability, High Mag-RF menu (high magic refine)
Overview: Alexander is the master of recovery. His revive command works just like a phoenix down, but completely restores a deceased character to life (that's why rating is 5/5 even though Alex doesn't do much damage...). High Mag-RF helps you create those difficult-to-obtain, high level spells (you must need Quezacotl's Mid Mag-RF to make low level magic into mid level, then into high level, or draw mid level magic from places--ex: 5 cura=1 curaga). Med data doubles the effects of any medicine; a hi-potion, for example, would restore 2,000 HP instead of just 1,000. Elem-Defx4 can make a character obscenely fortified. How does immunity to fire, ice, lightning, and water attacks sound? Thought so. ^^

Note: The next five GF you must get on your own, meaning that it's not part of the main uh...."thing". You don't HAVE to get them, but they do help (and are really cool!). Since this is the GF section, there won't be info. on exactly how to get them. For more info. on these side-quests, check the side-quests section in the walkthrough.

Doomtrain

Usefulness rating: 5/5
Location: Combine Solomon's ring with 6x Remedy+, 6x steel pipes, 6x Malboro tentacles
Attack: Runaway train
Element: Poison plus all status ailments
Useful skills: ST/Elem-Atk/Def junctions (status/elemental/defense attack junctions), auto-shell ability
Overview: Summoning Doomtrain afflicts foes with a wide variety of status ailments. That is to say, all of them. His ST-Atk-J, Elem-Atk-J, Elem-Defx4, and ST-Def-Jx4 junctions are all invaluable. Auto-shell protects a character from magic attacks.

Tonberry

Usefulness rating: 3.5/5
Location: Defeat 20 Tonberrys and Tonnberry king at Centra ruins
Attack: Chef's knife
Element: None
Useful skills: LV Up/LV Down command, haggle menu, sell-high menu, familiar menu
Overview: LV Up makes for a more difficult battle and more experience; LV Down weakens your foes and helps you win. Haggle makes merchants sell new items for less, while sell-high makes merchants give you more for used equipment. Familiar causes merchants to expand their inventories to include previously unavailable items.

Cactaur

Usefulness rating: 4.5/5
Location: Defeat Jumbo Cactuar on Cactuar Island
Attack: 1,000 needles
Element: None
Useful skills: Eva-J and Luck-J junction (junctions magic to evade and luck--whoohoo!), Luck+50% ability, bonus abilities (ex: HP bonus--+30 HP at level up, Str bonus--+1 Str at level up...)
Overview: Cactuar's damage strength is equal to the tens digit of his level multiplied by one thousand. For example, a level 47 Cactuar would deal out 4 x 1,000 or 4,000 HP in damage. Cactuar is the only GF that can increase your evasion and luck statistics, making him particularly useful for the game's intangible benefits. Cactuar joins with an innate knowledge of several bonuses, helping savvy players pump critical attributes.

Bahamut

Usefulness rating: 4.5/5
Location: Defeat Bahamut at Deep Sea Research Center
Attack: Mega flare
Element: None
Useful skills: Ability x4 (junction 4 abilities!), Str+60% ability (strength +60%), Mag+60% ability (magic +60%), rare item ability (more likely to get rare items), auto-protect ability
Overview: Bahamut's powerful nonelemental attack makes him an ideal guardian force to summon against nearly any foe. While he shares many useful abilities (such as mug) with other GF, his unique skills put him in a class of his own. Ability x4 turns one lucky character into a powerhouse. Rare items makes collecting those difficult-to-find weapon ingredients far less of a chore. And auto-protect gives a character an innate barrier, effectively doubling his resistance to physical attacks. Whoever receives Bahamut's powers becomes an unstoppable force.

Eden

Usefulness rating: 5/5
Location: Draw from ultima weapon at Deep Sea Research Center (after getting Bahamut)
Attack: Eternal breath
Element: None
Useful skills: Devour command, Expendx3-1 ability (cast 3 spells for the price of 1), GFAbl Med-RF menu (GF ability medicine refine)
Overview: Eden, the final GF, shatters the 9,999 barrier, potentially dealing nearly 40,000 points of damage to foes. The devour command has a low success rate, but if it connects, it can instantly kill any foe. Expendx3-1 lets a character cast a spell three times for the price of one. GFAbl Med-RF lets you create items that teach your GF useful skills

Note: The next 5 GF are actually Guardian helpers. They aren't summoned with the GF command and aren't junctioned like an ordinary GF. They arrive to help your party in a variety of different manners. Here are some members of the almost guardian force club. While they may not offer junctions or skills, they can mean life or death. (Sorry, no pictures.)

Phoenix
Usefulness rating: 2.5/5
Location: Shumi Village (do the Shumi Village side-quest and obtain the Phoenix pinion)
Attack: Rebirth flame
Element: Fire
Overview: After doing the Shumi Village side-quest, you obtain the Phoenix pinion. Use it in battle to summon the Guardian helper, Phoenix. This mystical bird deals massive fire damage to your opponent (at times), and resurrects any KOed party members (works like a phoenix down). After using it once, you will not be able to summon it again voluntarily. The following times it will appear will depend upon your character's luck statistic. This Guardian helper comes mainly when your whole party is KOed! O_o

Odin
Usefulness rating: 5/5
Location: Defeat Odin at Centra ruins
Attack: Zantetsuken
Element: N/A
Overview: Odin randomly appears at the beginning of battles to give your party victory. The frequency with which Odin appears also depends on your character's luck statistic. (See tips and tricks section for info. on how to raise your luck with Odin.)

Chocobo
Usefulness rating:1/5
Location: Find Chicobo in the chocobo forest
Attack: ChocoFire/ChocoFlare/ChocoMeteor/ChocoBuckle
Element: Fire
Overview: Use the Gysahl Greens to summon Chicobo to battle. Send Chicobo to the Pocketstation to level up and upgrade his attack.

MiniMog
Usefulness rating: argh! how would I know!? >.< (don't have a Pocketstation)
Location: Rescue Mog in Pocketstation game
Attack: Moogle dance
Element: N/A
Overview: Rescue MiniMog in the Pocketstation game, then give a guardian force the MiniMog command. It restores 1,000 to 1,500 HP to each equipped GF during battle.

Gilgamesh
Usefulness rating: 3.5/5
Location: Obtain Odin; defeat Seifer at end of disc 3
Attack: Zantetsuken/Masamune/Excalibur/Excalipur
Element: N/A
Overview: Noooooo!!! Don't die, Odin! Uh...lalala..>.< Anyway...Gilgamesh helps your party in a manner similar to Odin--only Gilgy has four attacks he can unleash. Zantetsuken is Odin's instant death move, while Masamune and Excalibur both hit all foes for significant damage. Excalipur is a joke attack that barely damages opponents.