Behemoth Mask

Behemoth Mask is head slot gear.

Source
Behemoth Masks can be obtained by exchanging 5 with the following vendors:
 * Aelina - Mor Dhona
 * Expedition Liaison - Eureka Pagos

Behemoth Masks can also be obtained during the Moogle Treasure Trove event by exchanging 30 with the following vendors:
 * Itinerant Moogle