I realize this is an old quest, but someone may be interested in doing this again someday.
First off, If your hunting him for the 'Orc Impailer' quest, then I assume your a ranger. Head over to the tower, and kill the shadowmen that spawn there.
Pull up track, and you should have one more shadowman up, even after you killed the ones at the tower. This is the placeholder for the Shadowman Leader.
I suggest you cast SoW or a fast mount, as the roaming placeholder moves very quickly and tracking it without a movement increase of some kind can be a serrious pain.
From what I can tell, he is on a 25 minute spawn timer.
This is a pretty simple camp, and the long spawn time and single placeholder allows you to watch Tv, Work on tradeskills, take a nap, etc. in between spawns.
I've been camping him all day. and as Axdin says you should clear out the shadowman camp. Three spawn there and never move, the PH roams around the northern/middle portion of the zone and depending on where you are standing and he is running you might pick up all 4 on track at once. The PH isn't higher level than the other shadowmen so filtering based on con level will not help you. He moves fast and frequently ran me into the trained brownie and other brownies.
Good luck if anyone else ever does this...Speaking of a tainted brownie running into me lol!
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