Aeons
An Aeon is a summoned beast. But Unlike other Final Fantasys once the creature is summoned, it can be used like a normal character. Each Aeon has unique abilities and attacks as well as distinct fighting styles.
Valefor
A large winged creature that's great at avoiding ground-based attacks. He is the first aeon Yuna receives on her quest to be High Summoner.
Special Attack: Sonic Wings - Damage and Delay Enemy
Overdrive: Energy Ray & Energy Blast
Exceed Max Damage: Find Yuna's ultimate weapons, the Nirvana
Location: Besaid Island
Ifrit
A great fire beast. Ifrit has been seen in many of the past Final Fantasys. His strong physical and fire damage is a great combo.
Special Attack: Meteor Strike
Overdrive: Hellfire
Exceed Max Damage: Find Wakka's final weapon, World Champion
Location: Kilika Island
Shiva
The queen of ice is always found in popular FF games. Shiva's strong ice element attacks and physical damage make her a great Aeon.
Special Attack: Heavenly Strike - Attack and Delay Enemy Turn.
Overdrive: Diamond Dust
Exceed Max Damage: Find Lulu's final weapons, Onion Knight
Location: Macalania Temple
Ixion
A strong lightning unicorn beast. Uses strong lightning elemental attacks.
Special Attack: Aerospark - Attack and negates spell effects.
Overdrive: Thor's Hammer
Exceed Max Damage: Find Kimahri's final weapons, Spirit Lance.
Location: Temple of Yevon-Djose
Bahamut
A strong fire dragon. Bahamut has always proven to be among the strongest of aeons, guardian forces, or espers. His high physical damage and fire attacks are always a good choice.
Special Attack: Impulse - Attack all enemies.
Overdrive: Mega Flare
Exceed Max Damage: Bahamut can exceed max damage automatically.
Location: Bevelle
Yojimbo
You must Finish Trials in the Cavern of the Stolen Fayth and then defeat Yojimbo in order to have him join your party.
Special Attacks:
Daigoro: Yojimbo's dog attacks the opponent.
Kozuka: The throwing of a knife.
Wakizashi: A giant slash of the sword.
Zanmato: The infamous "head chop-off" move.
Exceed Max Damage: Find Auron's final weapon, Masamune
Location: Cavern of the Stolen Fayth
Anima
Anima can be obtained by going to Baaj temple. Anima is used by Seymour in several encounters with him.
Special Attack: Pain - High chance of instant death.
Overdrive: Oblivion
Exceed Max Damage: Anima can exceed max damage automatically.
Location: Baaj Temple
The Magus Sisters
In order to get the Magus Sisters, you must first have the airship. Once you reach the Calm Lands, get a chocobo, head back to the ledge that leads to the Macalania Woods. They have one of the most ellaborate overdrives that deals a massive amount of damage.
Special Attack: Pain - High chance of instant death.
Overdrive: Delta Attack
Exceed Max Damage: The sisters can exceed max damage automatically.
Location: Remiem Temple