Cyberdemon: not natural fauna
The Cyberdemon was not found naturally occurring on the other side of The Portal. Several specimins were observed, however, in diverse areas in the portal environment.
The Cyberdemon is an alien creation which is half machine, half biological; a biological body modified throughout with mechanical structures. It has been proven through laboratory analysis of samples taken from three Cyberdemon corpses that the biological part of the Cyberdemon is based upon a heavily modified Satyrus Arenaceuscolorarea (Hell Knight) genetic set. The resulting Cyberdemon is much larger, has adaptative specializations, and bears only limited resemblance to the original Hell Knight organism. All three of the cyberdemons tested were found to be genetically identical, suggesting that all cyberdemons may be clones.
The Cyberdemon carries a large, rapid-generating Rocket Launcher on the end of its left arm. This device is extremely heavy, weighing around 600 lbs (272 kg), and furthermore, is front-heavy. The weight of this weapon is the reason for many of the mechanical additions to the Cyberdemon's body.
From the knee down, the Cyberdemon's right front leg has been replaced with a near-solid metal prosthesis, to provide extra structural strengh and, possibly, deliberate extra weight, for supporting and counterbalancing the weapon during firing and walking.
Within the Cyberdemon's body there are flexible metal support structures connecting the upper left arm to the upper part of the right leg. The tension of these structures changes at different times. While walking or standing, it has moderate tension, providing additional support for the weapon-bearing arm. When the Cyberdemon assumes its firing stance (with the metal leg forward and to the side), the tension is increased across the structures, providing increased support to help hold the weapon in the required upright position. At the moment the weapon is fired, the weapon pushes back and upward with tremendous force, and in that moment, the Cyberdemon subtly twists its upper body. This movement, performed while in firing stance, causes the internal structures to become locked at their existing length and completely rigid, providing maximum holding power against the massive forces being exerted by the weapon.
The Cyberdemon's eyes are positioned far apart, level with its horozontally-oriented horns which wrap most of the way around its head. This causes the Cyberdemon to have no useful peripheral vision, it can only see in front of it, in a narrow 60-degree wedge. This characteristic is nonexistant in the genetic base organism (Satyrus Arenaceuscolorarea), and is clearly a deliberate change by the Cyberdemon's creator(s). The limited vision angle is believed to force the Cyberdemon to squarely face its target in order to fire its weapon, as to attempt to fire the weapon angled more than 15 degrees either away from its body or across it would circumvent most of the mechanical support structures designed to help it stabilize and support the weapon. The widely seperated eyes also give the Cyberdemon greatly enhanced depth perception at long distances, enabling it to aim its rockets accurately at far away targets.
The reason for the lack of externally-located abdominal muscle is unclear. This area of the Cyberdemon is heavily reinforced internally with limited muscle mass and a large proportion of mechanical reinforcements.
Cyberdemons were found in varied environments on the other side of the Portal, in the company of different types of native organisms. It is believed to have the same nutritional needs as Satyrus Arenaceuscolorarea, which is omniverous. How these needs are met is a mystery, as cyberdemons have not been observed to have any interest in the prey species of the other side of the Portal.