You need to find Xer (or xeroth) In the corrupted lake. Which can be found in the Swamp, then the Forgotten temple, and then go undergrounds. Once your undergound in the corrupted lake you have to sneak around untill you find him. It might take a couple of tries but once you do, you then have to meet him at his underground hideout. Which can be found using the underground map, and its a dot located next to the swamp