FFX: Learning! Achievement
Learn to use all enemy abilities
Enemy abilities are learned by Kimahri as overdrives, and there are 11 in total to learn. To learn an ability, you must use Lancet in battle against them. You can get a number of these abilities during a single boss battle against two Ronso at the top of Mount Gagazet, while all the abilities are available from more common monsters as well.
A full list of the abilities and the monsters you can learn from can be found here.