Only a few of the aliens are on the warlords cycle(s).
To narrow the list of possible PHers, kill all "soldier" mobs, leaving the semi-named versions up. Kill all of them, even if you are only looking for one, all 3 types will cycle through.
Once it's down to 4 or 5 soldiers you'll get a warlord every 20m or so.
It is possible for the cycle to come up as a bat or dire wolf, however this was exceptionally rare in the few days I spent figuring this out. You can tell it's on the cycle though because it will respawn in 5m instead of 16m.