I have confirmed, to my own satisfaction at least, that Lord Elgnub is indeed a triggered spawn. I popped him three times by speaking with Marton Sayer about the quest in the cabin in Qeynos Hills. Each of the three times after talking to him I went directly to the spike pit in blackburrow and waited at the door. About thirty minutes later each time, Elgnub would pop in the tunnel leading to the green room. I never killed any snakes or other gnolls so he has no PH. I was also the only one in zone for 2 kills. Was very green to my 34 druid, never summoned a pet, and harm touched me off the bat for between 270-288 each time. He never cast any spells after that, though. Root, Drones, Immolate, and one combust later he was dead. Very easy kill. Always has Baby Joseph Sayer (lore/nodrop) like the mino hero always has the shackles. The intermediary gnoll slayer was changed to nodrop, so you had better have someone camped near who can use it. Pretty sure that the final slayer can be MQ'd but only by the character who has the sword. I tried handing it in once without the 2 drops from paw and Marton just gave it back to me.
Now I just wish there was a way to pop pyzjin :/