The mobs needed for the first step, a tormented Serillian spirit, only spawn during in-game night (8pm - 8am), and potentially have a very long respawn timer (~1 hour). They also run around where they spawn, so they won't necessarily be at their exact location listed, but definitely around that general area.
It is recommended that you make a targeting macro for the tormented Serillian spirits: /target a torment
Steps[]
Capture tormented Serilian spirits using Serilian Spirit Gems during game in-game night. At 0% health the spirit will fall down giving you about 2 seconds to select the target and use the gem. The gem has a 20 second reuse timer and if the spirit is left alone at low health it will heal and begin to run around again:
Mistmoore Catacombs: Ground floor in the water straight back from the zone-in near the climbable wall. ( 24, -161, 105 ) Copy/waypoint 23.80, -161, 104.72
Release the spirits back into their tombs in Kaladim's Underfoot Cathedral. Clicking a tomb will spawn a group of heroics, a ratillik Cathedral defiler (35^) and 2 Terrok bersekers (35^^):
( 10, 28, -505 ) Copy/waypoint 10, 28, -505
( 10, 28, -516 ) Copy/waypoint 10, 28, -516
( 10, 28, -527 ) Copy/waypoint 10, 28, -527
( 48, 30, -516 ) Copy/waypoint 48, 30, -516 (under a stack of stone blocks)
A discussion page exists which may contain more information