I beat mog ex like 10 times today so I know 100% how it works.

When warrior starts to use Moogle go round and the blue stuff on the ground appears, he puts a debuff on 2 random people - Bemoggled - massive damage taken from moogle go around, you need to ensuna it off the 2 people before it goes off and everyone takes 0 damage, DPS are focusing the WHM to interrupt holy at the same time.