Shade Elite enemy in the Rulanyil's Fall Dungeon, will only spawn if the player lights a brazier in the far room of the dungeon, triggering the group challenge. You will be assaulted by many skeletons with slows and aoes, so prepare accordingly.
Counts towards achievements:
Rulanyil's Fall Slayer - 10 points. Defeat three of the Champions in Rulanyil's Fall.
Rulanyil's Fall Group Challenge - 50 points. Defeat the undead hordes of Hergon the Fallen at Ruyandil's Fall.
Rulanyil's Fall Conqueror - 50 points. Defeat all of Rulanyil's Fall Champions.