Seymour Flux/Mortiorchis-Mt. Gagazet Before Cave Area...oh yeah.
Make sure that you have two Wings to Discovery, cast Haste, Protect, and Shell, have Tidus use Slice & Dice 9999x6 damage to Flux..
That guy is annoying since his super attack. But if you are a good level, go in with every Aeons overdrive maxed and overdirive his ass. He should drop after the third one.Use bahamut and if Valefor if you have the celestial weapon for Yuna, break damage is so helpful .
That worls for all of them. Anima, Valefor and magus sisters and Bahamut are all non element so wark against the last one. I killed that guy with anima alone.