"Unholy Light" is cast every 20 seconds (random target, but not most hated). "Bare Bones" is cast every 25 seconds (random target, but not most hated).
He spawned for me at -187, 339 in the two joined rooms to the SE of the spot marked here, as mentioned by earlier post. Easier to get adds here. Note that the rats seem to be non-aggressive and don't assist, at least not for a druid. 2 more to go for Hunter Achievement. Love exploring these old zones in pursuit of the Hunter Achievements but by the time I've killed the last named, I'm sick and tired of the zone lol.