Find the clue by opening a box and receiving Spectacles of Anti-Obfuscation in the Hall of Necromancy in Paineel at ( 1663, -267, 3175 ) Copy/waypoint 1663, -267, 3175. Equip the spectacles and then read the note on another table in the same room at ( 1657, -267, 3195 ) Copy/waypoint 1657, -267, 3195.
Either kill The Bonegrinder in Befallen: Cavern of the Afflicted and loot the Enchiridion of Undeath or acquire an Ulteran Diamond. The Ulteran Diamond is a rare jewel harvested in T9 zones. You can buy it from the broker, it doesn't HAVE to be harvested. Then speak to Arzachel and give him the item you chose.
Kill Dread Exarch Mordek in Befallen: Necrotic Asylum and examine the book you loot from the body. You must be in the zone while examining the book to get the update, and you must do the L90+ version of the zone to get the book to drop.
Brutus is found in the far northeast corner of Toxxulia's Reach, at ( -60, 126, 2783 ) Copy/waypoint -60, 126, 2783. Click the corpse to get your update.
Investigate the Sepulcher outside Windstalker Village in Antonica ( -1747, -13, -714 ) Copy/waypoint -1747, -13, -714. Enter The False Sepulchre and defeat the defenders. There will be grouped skeletons all around the room, and a pair of named bone Roper models guarding the chest. 4 groups of Heroic level 93 1 up in linked groups of 3. kills these 4 groups - spawns 2 L94 heroic double ups also linked. This final step is far easier if you have 1-2 people helping. very hard to solo this part.