Running out of ideas here. The dread guard mask and amulet are our best clues, but should we stress over the amulet? I put in a suggestion when 1.4 came out for a dread guard mask, and someone replied they've datamined one. But this amulet is probably the same thing. Not out yet. Maybe from NiM EC? Would make sense, go to all 3 places the dread masters have been involved. Denova for the amulet, Belsavis for the mask, and Asation for the cave.
Maybe? Who knows? All I care about now is getting a dread guard/hazmat body armor To go with the mask.