Stalkers are heavily altered Necromorphs, bearing little resemblance to their host's form. Their long arms are equipped with long talons ending in sharpened tips. While not very capable at slashing, they can still impale, knock down, and rend their victims. The ribcage is displayed wide open, though as with most Necromorphs, there is a lack of any digestive organs, and only vestigial remains of previously vital organs. Well-formed musculature in the back led to a reinforced spinal column and neck capped by the creature's most distinguishing feature: a massive, eyeless, three-pronged head with only traces of their host's bone structure. The skull is largely exposed, sporting a thick cap covered in bony protrusions to aid in crushing and bashing. The upper jaw and nasal cavities are left largely intact, while the cranial dome is squashed down to provide a more even, durable striking surface, which is further supported by the cheek bones. Unlike many Necromorphs, this highly mutated skull is the hardest point on the creature, and is immune to dismemberment. The legs have been heavily morphed, taking on a digitigrade structure and ending in two slender digits.

Following the death of the Brethren Moon over Tau Volantis, an alternate form of Stalker was encountered that exhibited a larger and bulkier morphology and a head crowned with large fang-like spines. These Stalkers were likely recombinated from another extinct species on Tau Volantis.