Moogle Beam. So it woudl have to be Yuna in Mascot dressphere.
– Ribbon does not protect against its Stony Glare. Nothing does. If a character is hit with its Stony Glare, cure it immediately with either Remedy, Soft, or Esuna or prepare for that character to be shattered. Watch out especially for Heaven’s Cataract.
– Disable its Heaven’s Cataract by getting into Oversoul. Oversoul form never uses Heaven’s Cataract. To oversoul it, fight monsters of the same type over at the temple ruins in Zanarkand (I believe that’s the right place.) Once you get one that oversouls, run away and then go try Chac again.