Lunar Shadestalker

I found Lunar Shadestalker howling by the entrance to Shadefallen Keep. If he has "spawned" he will come running towards you if you try to enter the keep. So if you enter the main gate and he has "spawned", he will spawn and run to the entrance from one of his back tents right inside the keep, to the left or from the upstairs wall. Stay in the first room and he'll greet you with a proper howl.