Adamastor

Notes:

 * Spawned by trading a Trophy Shield to the ??? at D-4 in the lower valley back behind a bunch of Gigas mobs.
 * If you wipe he moves back to his spawn and begins to regen. Got it down to 50% before wiping and it regened to 70% then despawned.  The ??? despawns after he is gone and doesn't come back until 5 minutes (roughly) later.
 * Used Standard Gigas moves, Also had an Auto EnSpell effect. He strongly favors Grand Slam using it 3 times in rapid succession around 30%.
 * The aforementioned effect could possibly be triggered by 2hr, our group did not notice any added damage until the NM was at 50% or lower.
 * Can drop a Treasure Chest after he is defeated.
 * Cannot be mugged.
 * Head Butt has low rate of landing, Temporal shift landed 100% Frypan and Tailslap were ineffective.
 * Has a high (90%) Double Attack rate.

Hystorical background
Adamastor is the name of a giant in the portuguese epic Os Lusíadas, meant to represent the hardships inflicted by nature and geography that sea ship crews would face during difficult trips.