The Cyborg is an enemy encountered throughout Marathon 2: Durandal and Marathon Infinity.
The Cyborg appears to be a combination of organic and machine parts. The upper half is somewhat humanoid in appearance, with cybernetic enhancements on the arms, including a grenade launcher. The bottom half resembles a tank with triangluar formed treads and a red or green strip of light on back of the tread section. When destroyed, it is revealed that the two halves appear to have been connected by a series of pipes.
In combat, the Cyborg uses its wrist-mounted grenade launcher to attack, launching slow-moving bouncing grenades, which are relatively easy to dodge. The more advanced versions of the cyborg attack with a wrist-mounted flamethrower when within close range, and the grenades of these advanced cyborgs (which bear green markings instead of red) are heat-seeking.
The Mother of All Cyborgs is an even bigger variant of the Cyborg with more health, seeking grenades and a flamethrower.
The assault rifle takes many rounds to destroy one of these, but the Cyborg will typically be unable to return fire while being repeatedly shot. The Zeus Class Fusion Pistol also seems to affect them more than many other weapons, as it tends to do with machinery in general. Be aware, however, that Cyborgs explode when destroyed, causing damage to anything nearby. A Rocket Launcher is less effective against Cyborgs as they survive a direct hit with just enough health on normal. So you'll have to finish them with pistols.
- Originally, the Cyborgs were envisioned as captured BOBs who were radically, surgically altered by the Pfhor, using the player's stored "pattern" as a template. Although unaddressed in-game, this backstory still seems to hold up in the existing storyline's framework.