There are twelve Eidolons (summons) in Final Fantasy 9 and two characters capable of summoning them. Dagger and Eiko each have specific eidolons that they can summon. Some eidolons only have one attack but others can change their attack depending on which add-ons or support abilities are equipped. When an eidolon is first summoned the full summon animation, where we actually see the eidolon appear, will play. This boosts the eidolon's attack power. Thereafter the full eidolon animation will appear only some of the time. However, Eiko and Dagger can both learn the Boost support ability. When equipped, Boost causes the eidolon to appear every time it is summoned.

Shiva's attack power is increased for each Opal you have in your inventory. These are dropped by monsters and they can also be synthesized by Hades. Shiva attacks all enemies with an ice elemental attack.

Ifrit's attack power is increased for each Topaz you have in your inventory. These are dropped by monsters and they can also be synthesized by Hades. Ifrit attacks all enemies with a fire elemental attack.

Ramuh's attack power is increased for each Peridot you have in your inventory. These are dropped by monsters and they can also be synthesized by Hades. Ramuh attacks all enemies with a thunder elemental attack.

Atomos attacks by reducing all enemies' HP by a percentage. The formula for the percentage depends on the number of Amethysts in your inventory. It also depends on whether the eidolon appears. The formula is as follows: Eidolon - (30 + # of Amethysts)% of enemy's HP; No Eidolon - 2/3 of Eidolon formula.

Odin will normally attempt to KO all enemies. The percentage for the success of KO is as follows: Dagger's magic power/4 + difference between Daggers' Level and Enemies' Level. After visiting Ipsen's Castle in Disc 3 and finding the Ancient Aroma Dagger can learn the support ability Odin's Sword. With this equipped should Odin fail to KO an enemy he will use a Wind attack to damage the enemies.

Leviathan's attack power is increased for each Aquamarine you have in your inventory. These are dropped by monsters and they can also be swapped for Ore at the Daguerreo wall engraving. Leviathan attacks all enemies with a water elemental attack.

Bahamut's attack power is increased for each Garnets you have in your inventory. These are dropped by monsters and they can also be synthesized by Hades. Bahamut attacks all enemies with a non-elemental attack.

Ark is Dagger's ultimate eidolon. It can only be learned from a Pumice that must be forged by Hades from two Pumice Pieces. Ark attacks with Shadow damage to all enemies.

Carbuncle is the only defensive eidolon in the game. Carbuncle can cast Reflect, Haste, Protect, or Vanish in the party depending on which gem Eiko has equipped as an add-on. When a Ruby or no gem is equipped on Eiko then Carbuncle will cast Reflect. An Emerald equipped will cause Carbuncle to cast Haste on the party. With a Moonstone equipped Carbuncle will cast Protect. Lastly a Diamond will cause Carbuncle to cast Vanish on the party.

Fenrir attacks with either Earth or Wind element depending on which add-on Eiko has equipped. Normally Fenrir does Earth damage to all enemies. However, if you've equipped the Maiden Prayer Fenrir will cause Wind damage to all enemies.

Phoenix does Fire damage to all enemies and revives any KO'd party members. Also, once Phoenix has been summoned once there is a possibility that Phoenix will appear to revive a completely KO'd party. The formula for the probability of this occuring is as follows: # Phoenix Pinions in stock divided by 256 = % chance of Phoenix appearing.

Madeen is Eiko's ultimate eidolon. It can only be learned from a Ribbon, which Eiko receives on disc 3. Madeen deals holy damage to all enemies.