Just to clarify, this spawns in the room that's shaped like an "H" on its side (i.e. you want the room to the right/east of the Undertaker Lord's room). Two mobs are up in each of the four alcoves.
Respawn time on the Sketch is less than 40 mins - suspect 20 as that's HS's mob repop time.
Edited, Nov 13th 2017 8:27am by CantabileAutotune