Known spawn locations (click for map image -- PH "a soul taker") for your "ethernere.txt" map file (note for all known Ethernere Tainted West Karana named spawn locations, see this quest entry):
P 4495.1519, 1328.8987, -455.6906, 127, 0, 0, 1, Soul_Sifter
P 4450.5801, 1508.8400, -455.3400, 127, 0, 0, 1, Soul_Sifter_(roam)
One of his casts flings the entire group onto him, we think at the same time. Lots of merc and caster deaths when this happens, which was about every 30 seconds. Pet tanking is very hard with this mob.