The Ratslayer is the unique variant of the varmint rifle. It has a black synthetic stock instead of the standard wood, parts that appear to be made from stainless steel, and has a rat skull with 69 hatch marks on the stock.
Inside the Broc Flower Cave, on the upper level, below a desk in the makeshift laboratory. It may be quite hard to find as there are lots of giant rats in this room. With the Wild Wasteland trait, the area containing the Ratslayer will have several unique giant rats.
The Ratslayer has a very high critical multiplier of x5, making it the gun with the 3rd highest multiplier (after alien blaster and Euclid's C-Finder). This fact alone makes the Ratslayer a very powerful gun, a player with a critical chance of 20 (or higher) would score a critical strike on every successful hit.
The Ratslayer also has the smallest spread of any 5.56mm chambered weapon, making it a valuable choice for sniping targets at great distance.
PCXbox 360 It appears that the night vision scopes for varmint rifles work off of the in-game clock, making them activate at 6:00pm, while the sun doesn't go down until around 7:00pm.
Xbox 360 When using the "player sight" final/first kill cam, the scope will momentarily turn clear, no matter what time of day it is.
PC The onHit effect for this weapon is defined as "Dismember only" (the weapon will only calculate the chance to sever limbs), as opposed to the varmint rifle, which uses "No Dismember/Explode" onHit effect (all limbs hit by the weapon will remain intact). There is a bug associated with the "dismember only" effect, which will immediately alarm all enemies in the vicinity of the killed enemy. This is not triggered by the sound level of the Ratslayer, which is the same as the standard varmint rifle's sound level, but by the onHit effect itself. Because of this bug, this weapon is mostly useless for sneak attacks, as only one sneak attack is possible before enemies become alarmed.
PlayStation 3 When looking through the scope, the screen might be seen as green and pink, making it impossible to use the scope. This may happen on any scoped weapon (including binoculars). To fix this, just save the game, shut down your PS3, then restart the game and the problem should be fixed.
PlayStation 3 When killing a group of enemies in Sneak mode, one of them may become an 'Ash pile'. This is random occurrence, and was only mentioned here after it happened more than 10 times in one playthrough.
Xbox 360 There is a bug that only happens while; being in third-person, in motion, wearing the NCR Ranger patrol armor, and holstering the Ratslayer. The weapon clips inside your body and only shows the barrel of the gun protruding through your left shoulder. This can be fixed by drawing your weapon, stopping motion, and holstering your weapon again.