Dark Aeons are optional bosses in the PAL version of Final Fantasy X. They are exactly as the name says: evil versions of aeons, controlled by the monks of Bevelle. The good thing is that unlike previous aeon battles, the same aeon that is being battled can be summoned. The bad thing is however that to defeat them the Sphere Grid needs to be fully customized, which can be difficult. It is possible to defeat them using a non-customized grid, however it is very hard, and then it is difficult to beat the ultimate boss of the game, Penance.
Penance is just as it sounds, the hardest optional boss in the game and will take over one hour to beat. To fight him all other dark aeons must be defeated and then it will appear as a location on the airship.
NOTE this is only available for the PAL version of the game.
For more in depth details about Dark Aeons, please visit the Dark Aeon FAQ by Steaver370.
One quick and easy method to defeat the dark aeons is to get Yojimbo from the Cavern of the Stolen Fayth and pay him exactly 1/3rd of the party's gil and he will 98% of the time use Zanmato which will kill any Dark Aeon, Boss, and Penance.
 Recommended Armor
- Break HP Limit
- Auto Protect
One character should also have Auto-Phoenix instead of Auto-Haste, the other three are a must.
 Dark Aeon Locations & Strategies
For detailed locations of each of the Dark Aeons, as well as strategies on how to defeat them, visit their relevant pages:
Related ThreadsAnima and the dark aeons. - last post by @ Jun 4, 2008
The Final Fantasy X Official Guide Dark Aeon Section - thanks for nothing! - last post by @ Jun 29, 2006
Dark Aeon Discussion - last post by @ Sep 9, 2005
Dark Aeons-Celestial Mirror-Anima-HelpMePlz - last post by @ Jun 23, 2010
fight dark aeons in american version (i think) - last post by @ Aug 4, 2002