Fiends are monstrous beasts with a heavily armored carapace. Unlike the stealthier Wraiths, Fiends are besieging units that attack head-on, scattering enemy forces and destroying entrenched enemy positions. They attack non-kett without appearing to need orders; some scientists believe Fiends respond aggressively to an absence of kett pheromones or similar cues.
A Fiend's carapace is permeated by dense cartilage that makes it both strong and flexible, and acts as a shock absorber for incoming fire. Preliminary study of their nervous system suggests that nerve transmission is dampened above a certain pain threshold, allowing a Fiend to detect injury but not be slowed by it. Reports of Fiend encounters are often accompanied by casualty lists, and the militia advises that only a well-armed and organized team should handle a Fiend at full rampage.