(Disturbed) Tyrannical Warlock

Lore
His quest for strength brought him to night-fallen Runevalis. As the warlock surveyed the grim wasteland, he realized a golden opportunity. He could sense the presence of countless powerful foes, practically begging for him to bring them down. He could scarcely contain his anticipation as he began his passage.

Acquisition
?

Additional Info
Boss during the Stranger in a Strange Land Raid Event (see Stranger In A Strange Land Raid Bosses)