An Acolyte. Note extensive cybernetic upgrades.
The Acolyte is extremely skinny, with patches of muscle visible on his body. Most are amputees due to unknown reasons, with lost limbs replaced with mechanical prosthetics. Their heads are partially embedded in a metal helmet grafted onto the skull with a single red lens responsible for the sense of sight. In extreme cases, the brain is exposed and clearly visible. Being more advanced than their initial brethren, acolytes have better combat skills and improved cognitive processing.
The Acolyte is capable of using weaponry like a regular soldier (most often a Tiberium Auto Rifle), but the command algorithms and augmentation process do not guarantee his loyalty, as is the case when mutants turn on their creators in a Nod research facility, when captain Nick Parker attempted to rescue doctor Ignatio Mobius.
The Acolytes are mid-level mutant adversaries. They are fast and accurate with their Tiberium auto rifles and tend to come in packs. Fortunately, they aren't nearly as resistant to damage, making taking them down very easy.
In multiplayer, they are available to Nod on extras-enabled servers.
Interestingly, a GDI version of the mutant (complete with a skin and configuration) is present in the files, but not in the actual game. The mutant is stronger (with 200 hit points, as compared to the 150 for Nod), but is only armed with a pistol.