It’s one of the legendary items or more precisely a legendary accessory which is pretty cool. Out of curiosity I opened what I could of the game files and under legendary item files is the Emperor’s armor and helmet as well as Spoilers ahead: Davkul’s armor and mask which I think hasn’t been found yet.Davkul is mentioned in the game by the cultists “Ph’nglui mlgw’nafh Davkul R’lyeh wgah’nagl fhtagn. Nn’nilgh’ri, nn’nglui. Sgn’wahl sll’ha ep’shogg” which has been translated by some folks as “In his house at R’lyeh, dead Davkul waits dreaming. Watch the threshold. The realm of darkness shall be upon us all.” which means it’s possibly tied to the undead invasion or something even more sinister. If it’s the set that I think it is, it’s pretty dreadful and horrific, in a good way. Can’t wait to discover its stats and effects.
Actually someone found the Davkul helm, go check: https://steamcommunity.com/app/365360/discussions/0/135511913390997445/
