Once you’ve dispatched all the Silent Legion skeletons in the area, it’s possible to cheese the King’s Niche boss. He can’t get through the doorway at the top of the stairs to the room he’s in. With patience a player can eventually get the thrall of their choice to agro on the boss. The whole battle takes place in the doorway with no fear of the player taking any damage. The player can also opt to take the boss out but this requires even more patience.
The poor design is obviously that the boss can’t get out of the room he is in.