Kill 12 Nightbane Dark Runner worgen for Calor in Darkshire.
You might have noticed some larger worgen wandering around with the Shadow Weavers in the woods? From what we can tell, these Dark Runners make up the bulk of the worgen numbers.
On my rangings, I've also noticed that they have overrun the Rotting Orchard southwest of town. These worgen are a bit tougher than the last you faced.
Be on your guard.