Rattlers are all through these woods. I can't risk getting chained up again.
―A runaway's fears of the Rattlers.
The Rattlers are a militaristic gang of slavers based in Santa Barbara, California, who serve as the final antagonistic faction Ellie Williams and Abby Anderson encounter in The Last of Us Part II.
Some time after the outbreak of the Cordyceps brain infection, the Rattlers were created. They are a heavily armed group of hostile survivors who have set up camp in an oceanside resort in Santa Barbara, California. They also occupy and patrol the suburbs and woodland areas. Their base of operations is the dome within the city, formerly a hotel that the Rattlers converted into a fortress and slave labor camp.
They have traps set up across the city to catch infected and humans alike, with the former chained up and used as guard dogs while the latter are forced into slavery. Those who resist too much are sent to "the pillars", wooden beams set out on the beach where they are strung up and left to die from exposure to the elements. Those who did escape harbored a deep hatred for them, some even plotting to gather a group together to attack the Rattler's dome.
The Rattlers are sadistic in nature, some intentionally infecting slaves and chaining them up for their amusement. The Rattlers treat their victims with such cruelty that dying in an escape attempt is preferred by some. Those who do escape are dubbed "runaways" or "strays" that the Rattlers chase to recapture. They purposely harm slaves in a way that wounds them but does not kill them, evidenced by one Rattler stopping another from beating Abby to death with a bat and a patrol leader instructing her squad to shoot runaways in their legs to stop them running. Despite this, some were still willing to join the group as it secured them protection for their family.
Given the fate that awaits those captured, some runaways steal guns to commit suicide. In fact, numerous notes can be found in the area written by residents who either escaped or killed themselves to avoid being captured. As such, they are one of the few groups in the game that lack morals and are known for their villainous nature.
Events of The Last of Us Part II
A couple of months later, Ellie is caught in one of the group's traps while searching for Abby. She is found by two Rattlers, the same men who captured Abby and Lev, hours later, who cut her down and plan to take her back to their base. However, she takes advantage of one Rattler's attempt to scare Ellie by pushing her into a hanging clicker, helping the clicker bite him to death and then takes his silenced submachine gun to shoot the other Rattler in the legs. She then interrogates him for information regarding Abby's location before executing him.
During this time Pat wrote a letter to Jenny revealing they had captured a few strays recently. Ellie encounters one such stray patrol before pushing through, reaching the Rattler base along the railroad tracks, a dome-like building. Sneaking her way in and then fighting through the Rattlers inside, she reaches the cells where the enslaved people are kept. In a brutal fight, she manages to defeat the Rattler guarding the cells and (despite one prisoner wanting to kill her) learns that Abby and Lev attempted to escape to the boats at the beach. The prisoners, finally free, steal several guns from the supply room and then launch an assault on the Rattlers, setting the mansion ablaze and killing many of them outright in revenge.
As the final enemy faction in Part II, the Rattlers serve as the toughest group in the game. Their use of body armor, automatic rifles, pistols, shotguns, Molotov cocktails and large numbers make them a difficult group to overpower. However, given their careless nature in having infected within their grounds, Ellie is able to set them loose to attack, distract and kill Rattlers in the mansion.
Their biggest strengths are their large numbers and numerous traps, which make evading the group difficult and dangerous as players can trip on land mines in the surrounding area. Further, the patrols outside the mansions searching for fleeing slaves possess guard dogs that can (similar to those used by the Washington Liberation Front) effectively track the player's scent, forcing them to constantly move through the area to evade detection. The main difference is that these dogs wear bulletproof vests, which forces the player to kill them with multiple shots or a headshot.