Night stalker Night stalkers are living in the Mojave Wasteland and Big MT in 2281 . Characteristics . Biology . Night stalkers are the creations of Dr . Borous in the Z - 9 Crotalus DNA preservation lab of the Big MT , and are genetic hybrids of rattlesnake and DNA . They growl , howl , and whimper like regular coyotes , but hiss , rattle , and inject venom into their prey like snakes . 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 , which can be used to prepare Mushroom Cloud . Their blood is also used as an ingredient in antivenom and hydra . Night stalkers nest in caves across the Mojave Wasteland and can be found both inside the cave or in the nearby area . Packs of night stalkers can be frequently seen hunting at night east of Morning Star cavern near the nest with the , south of the broc flower cave , and northwest of the cap counterfeiting shack . Their original breeding ground is the Z - 9 Crotalus DNA preservation lab , located in the Big MT . Gameplay attributes . When they detect the Courier , they may strike with a leaping attack and a venomous bite or snap at them without leaping . While the venom is not as potent as that of their main competition , the cazador , it can pose a serious problem if multiple bites are received and aren ' t promptly treated . However , this can be avoided with the Animal Friend , as night stalkers will not attack you . Night stalkers can pose a particular threat in areas of low visibility , at night ( when they are active ) or in caverns . They are especially dangerous inside their dens ; packs are usually large in numbers , and twisting corridors make it difficult to detect exactly where they are . Night stalkers found in Charleston cave and the lower level of the X - 13 research facility have the ability to cloak , making them especially dangerous . The ones in Charleston cave gained this ability from chewing on a , while the ones in the X - 13 testing facility had the ability granted by an unknown scientist . As with any other cloaked enemy , these night stalkers can only be targeted in V . A . T . S . with the Enhanced Sensors companion perk provided by ED - E . It should be noted that their invisibility will not prevent them from causing ripples in any body of water they move in , hindering their ability to execute an ambush attack . Night stalker packs can be found in : Variants . Night stalker . Night stalkers are the size of s with a canine body and the head and tail of a rattlesnake . Night stalkers nest and hunt in packs and are found in or near their cave nests . Young night stalker . In appearance , young night stalkers are visually identical to fully grown night stalkers , but are smaller in size and have weaker attacks and less Hit Points . Although relatively weak , they are a nuisance when fought in groups of other young night stalkers and their fully grown brethren . Legendary night stalker . The legendary night stalker is a very large and very strong night stalker found in Bloodborne cave , which is west of Bitter Springs . In appearance , it is visually identical to standard night stalkers but differs only in size , being about the size of a bighorner . It is normally encountered in a pack with several regular night stalkers and young night stalkers and can kill a low level character in seconds . It has the least amount of health out of all of the , but can kill a player character under level 20 with about two to three bites . It is also the only legendary creature in the game that can be friendly towards the player character if they have acquired the Animal Friend perk . Den mother . In some night stalker nests , such as Morning Star Cavern , the pack will be led by a den mother , a slightly larger female night stalker who looks after the young , and has a much stronger attack than standard night stalkers . If her young are harmed , she may go into a frenzy similar to that of the . Appearances . Night stalkers only appear in " " and its " Old World Blues " .