Dark Aeon

The International and PAL versions of Final Fantasy X included several extras that were not available in the North American edition. One of these extras was the option to fight the Dark counterparts of each Aeon featured in the game.

Appearance of the Dark Aeons
Once Yuna and her Guardians escaped from Bevelle, they were branded as traitors of Yevon and orders were given to stop their pilgrimage and arrest them at all costs. After defeating Yunalesca at Zanarkand and gaining control of the Airship, you are free to return to any location and look for new areas to visit. The eight Dark Aeons were summoned to halt your journey, some were blocking your entry to previously friendly locations, while others were merely wandering in inconspicuous locations, hoping you would come across their path.

Each Dark Aeon boasts upwards of 800,000 HP, with Anima taking the honours with 8 Million. They each have close to maximum stats and are immune to all status effects. All drop weapons and armour with Break Damage Limit and Break HP Limit along with other high-level auto-abilities such as Ribbon. In the case of Yojimbo (whom you must defeat 5 times in a row), he can be fought an unlimited amount of times to fill up your stock with many excellent weapons.

Dark Valefor
A nice trip home for Yuna, Lulu and Wakka is no happy reunion as at the gates to Besaid Village, a summoner disallows you entry and then summons Dark Valefor to give you a nasty welcome.

Dark Ifrit
This angry beast is somewhat off the beaten track, as he is waiting at the entrance to the now-inaccessible Home. It seems that even some of the Al Bhed are now against you: if you speak to the woman near to the entrance she will ask for your assistance, luring you into a trap where Dark Ifrit pounces if you try to peer over the edge of the canyon.

Dark Ixion
For those who like the sound of rumbling thunder, a stroll through the Thunder Plains is likely to get you into trouble with Dark Ixion, who has obviously been bulking up on the constant lightning. To make matters worse, he is a bad loser, and will return for a second round after he has been supposedly defeated. However, eagle-eyed players will be able to spot him waiting in the distance, so unless you are ready and willing to jump into the fray again, you will wisely back off and leave the demented unicorn for another day.

Dark Shiva
After killing their leader, Maester Seymour, the Guado are certainly not going to let you back into Macalania Temple and summon Dark Shiva to give you the cold shoulder. Even if you are quick enough to ward off the Ice Woman, the Guado then try to get rid of you themselves.

Dark Bahamut
Once Yunalesca is out of the way and you fly off into the sunset on the Airship, Dark Bahamut will take pride of place in The Beyond, patiently awaiting your foolish return. Unless you have worked hard on the Sphere Grid and can boast about getting rid of at least the previous 4 Dark Aeons, Dark Bahamut will consider your party nothing more than annoying mosquitoes and squash you with little effort.

Dark Yojimbo
A nostalgic visit to the Cavern of the Stolen Fayth sounds like a good idea. Perhaps you are collecting fiends for the Monster Arena, or picking up some treasure you missed the first time? You had better watch your back because a summoner is sneaking about and is not going to let you leave without a fight. Don't forget that Dark Yojimbo is an ancient warrior and he likes to attack fast and early, so you may be facing a quick death before you even realise who you are fighting.

Yojimbo operates on the Best-of-Five principle. After his first defeat, the Summoner will reteat back through the Cavern. Follow him to initiate another battle. Yojimbo must be fought 5 times in a row without leaving the Cavern or stopping the game, however you are free to use the Save Sphere to regenerate the party and save the game. After the fifth victory the Summoner will leave for good.

Dark Anima
The Gagazet trials were fun, especially the target throwing with Wakka. If you want to brush up on your hand-eye coordination, feel free to try again and reap the rewards. Unfortunately the reward is Dark Anima who will appear as you return to the entrance of Mt. Gagazet, cold and menacing with a devastating Pain attack that even Deathproof won't shield.

Dark Magus Sisters
Facing one Dark Aeon is tough enough, but three at once? You have to be kidding! Unfortunately the Sisters are not, and will ambush you if you cross their paths on the Mushroom Rock Road.

Penance
Once you have dispatched all the other Dark Aeons to the Farplane, the toughest enemy in perhaps all Final Fantasies will arrive to throw down a challenge. Do you dare to take up the offer?

Final Fantasy X-2
The Dark Aeons (sans Penance) returned for X-2 as bosses but are nowhere near as formidable as their previous versions. They are manifested as a by-product of Shuyin's hatred for Spira and appear in their respective Chambers of the Fayth in Chapter 3. The exception to this is Shiva, Anima and the Magus Sisters; because their temples are inaccessible, they are encountered when the party enters the Farplane. Dark Yojimbo is the only aeon you are not required to fight, you can choose to ignore the mission in the Cavern if you wish.