Nightstalker Dire Rats

"The thing that steps out of the shadows seems to be a wolf at first, but as the smooth head stretches towards you, razor sharp mandibles bared, it becomes clear that this is a massive rat, maybe the biggest rat you've ever seen. Something is wrong with this creature: its eyes glow deep red and the body is encased in a glistening shell, like some sort of armored insect. Wherever the shadows touch its form, the creature seems to dissolve slightly, as if becoming one with the shadow."

Skulking Predators

Unlike the wretched, parasitic, filthy creatures of the city, nightstalker dire rats are fearsome predators in their home environments. A wise traveler's worst fear is to hear the eerie, bone chilling cry of a dire rate from outside the light of the campfire. Once they surround you, the swarm does not easily let prey escape. It is suspected that the nightstalker rats came from another plane, as no similar creatures exist in the fossil record.

Dangerously Social

Nightstalker rats prey on creatures of Medium size and smaller, working in packs to bring down large prey. As many as 10 rats can be found in a single nest: these larger nests are known to prey on caravans or farmers carrying food.

One with Shadow

When prowling at night or in dim areas, the creatures seem to become almost one with the shadows, moving incredibly fast in the darkness. The wise adventurer carries extra torches when venturing into their territory.

Ties to the Praetoria

After the Departed encountered a nest of nightstalkers while investigating a wounded thunderhoof unicorn, they found a tattered note on a charred Praetorian paladin's corpse. Most of the contents were burned away, save for a few words that Loghain was able to salvage: "...nightstalkers...thunderhoof...retreieve horn...the...-fell..."
Source: Mutated Monsters