Tiberian fiend

The Tiberian fiend is a Tiberium-based lifeform appearing in Tiberian Sun and the Firestorm mission pack. They are vicious ambush predators that live within dense Tiberium fields.

Background
Tiberium fiends are large, doglike animals that inhabit the Tiberium-infested zones, preying on local game and occasional passersby. They hide in Tiberium fields and are perfectly camouflaged from visual detection thanks to the Tiberium crystals growing on their hides. The fiends are highly territorial, and will attack anything that passes too close to their domain.

Physiology
Tiberian fiends are one of the many indigenous Earth species (humans aside) that have suffered some degree of Tiberium mutation. They typically stand about 5 feet tall at the shoulder, weigh around 400 pounds and have black or irridescent red skin. Their eyes glow an eerie green when struck by light at a certain angle, and their heads are elongated like a crocodile, their mouths full of sharp teeth. Their sheer size and strength suggests most were originally either canine or equine.

Like most other land-based Tiberium-mutated life forms, their muscular and skeletal systems are much denser, making them much more resilient and highly resistant to physical damage. They are also much faster and stronger, and can easily outrun a biped, with their immense strength enabling them to dismember and/or disembowel their target - often with a single swipe, though they most often attack from range. They are generally avoided by human populations, for good reason.

A Tiberian fiend's back is coated with a dense mat of pure Tiberium crystals, which serves two purposes. Firstly, it allows them to conceal themselves within a Tiberium field - only experienced soldiers can identify the telltale signs of a nesting fiend before it's too late. Secondly, the fiends can somehow launch shards of this Tiberium at enemies and prey via high-pressure ducts in their snouts. Though the shards are not very aerodynamic, they're sharp and dense, easily puncturing personal and even vehicular armour. Worse, as the shards can easily embed into the wounds they create, acute Tiberium poisoning is almost guaranteed.

As a Tiberium-based lifeform, Tiberian fiends are almost impossible to harm with Tiberium-based weaponry; in most cases, it simply causes them to heal more quickly.

Whilst their teeth can rip and tear through even Tiberium-enhanced flesh and reinforced metal, fiends seem to prefer to attack from a distance.

Social structure
Those who have observed Tiberium fiends and lived to tell about it report that they have a social hierarchy similar to pack animals, such as wolves, often with a dominant Alpha pair and a number of lesser members subordinate to them. Though there is nothing to indicate the existence of Omega members, ones who diffuse tension through play or other means to prevent the packs from destroying themselves, those observed appear to stable and healthy.

Psychology
Tiberium fiends are extremely aggressive and territorial. They will attack anything that is not affiliated with their pack that comes into their territory the moment they become aware of it, regardless of whether the intrusion was intentional. In cases where the packs are threatened, they will face the threat head-on with the single-minded intent to kill or be killed in defense of the pack.

They are ambush predators, lying in wait for their prey and then pouncing on it at the last second. They lurk in and around Tiberium fields, the crystals on their backs enabling them to blend seamlessly with their environment and rendering them invisible to the untrained eye. They will also burrow into Tiberium fields, making it impossible to tell whether patches of the crystal are unoccupied until it's too late.

However, they are apparently intelligent enough to recognize acts of kindness, and the Forgotten have used this to great advantage in domesticating them to the point of being just aggressive enough to serve as watchdogs. They run in groups of four to eight with a member of the Forgotten who is the Alpha of a particular group. The fiends will not respond to the commands of anyone else and will go berserk if their trainer is killed.

Game unit
Tiberium fiends are unusable units that seemingly come out of nowhere and attack with impunity, using ambush and swarm tactics to overwhelm and destroy the units of unsuspecting players. Since they are much more resilient and powerful than most infantry units, it's generally considered smart for players to keep their own away from them and retaliate with anti-infantry vehicles or provoke them into giving chase and drawing them within range of anti-infantry defenses. They can be crushed by vehicles heavy enough to do so.