Night stalkers are the pre-War creations of Dr. Borous at Big MT, being genetic hybrids of rattlesnake and coyote DNA. Dr. Borous created them in order to preserve the DNA of rattlesnakes, which he believed to be on the verge of extinction. However, his memory was unclear, and he also suggested that it may have been because of a dare with Dr. Calis at X-13.

Due to their creation, the shipping department of the X-8 research center suffered a large number of fatalities, where all but one employee were killed by the night stalkers. However, Dr. Adam Figgis thought the executives in charge of X-8 could salvage the mishap in shipping and decided to let the night stalkers loose into the X-8 testing area to study their behavior.

Sometime after the bombs dropped, a large night stalkers escaped and have spread across the wasteland, Night stalkers occasionally clash with cazadores (which were also created at Big MT) over territory.

Biology

Nightstalkers are an amalgamation of the coyote and rattlesnake, displaying characteristics of both. They growl, howl and whimper like regular coyotes, but hiss, rattle and inject venom into their prey like rattlesnakes. Their bodies are mostly dog-like, covered in a combination of fur and scales. Their heads and tails, however, are more like that of a rattlesnake, including fangs and a forked tongue. Night stalkers' right eyes are blue with a round pupil, while their left eyes are yellow with an elliptical pupil, like a rattlesnake's. They lay eggs, like a snake, but raise their pups similar to a coyote, nursing their young in cave nests.

As their name suggests, night stalkers are largely nocturnal, hunting in packs at night for unware or sleeping prey. However, it's still possible to encounter night stalker packs during the day. Night stalker eggs can be used to prepare Mushroom Cloud. Their blood is also used as an ingredient in antivenom, hydra and nightstalker squeezin's.