What Pellegri said but this does remind me of a 1.0 mechanic. In the Nael Deus Darnus (Hard) fight in 1.0, you had to craft Deaspected Clusters into Lunar Curtains in order to survive Mega Flare. Is it possible that there's some unique consumable that's being missed? Maybe it drops from mobs in turn 3? I don't see any good candidates in xivdb but maybe it wasn't parsed from the DATs properly?
