|“||Into every generation, there is a chosen one. One girl in all the world. She alone will wield the strength and skill to stand against the vampires, the demons, and the forces of darkness; To stop the spread of their evil and the swell of their numbers. She is the Slayer.||”|
— The prophecy of the Slayer
Slayers are young female humans bestowed with mystical powers that originated from the heart of a demon, which gave them superhuman senses, strength, speed, endurance, agility, healing and occasional prophetic dreams in the fight against forces of evil. While known primarily as the "Vampire Slayer", the Slayer also acts as a hunter of evil mystical forces in general (demons, bad witches, etc.).
Originally, there was only one Slayer in existence at a time, because for there to be another Slayer, the previous one would have to die for her powers to be inherited. Because of this, Slayers were often referred to as the Chosen One. This process continued for thousands of years until the intervention of Buffy Summers in 2003.
Powers and Abilities
Slayers were endowed with increased physical strength greater than that of average adult humans, some demons and most, if not all, vampires.
Much like vampires, the Slayer's strength seems to be largely metaphysical, as it does not add to their body mass and they remain buoyant enough to swim.
It appears that Slayers are able to access even greater levels of strength when upset or angry.
Speed, Agility, and Reflexes
Slayers are able to move faster and react more quickly than humans and most vampires.
A Slayer is capable of superhuman feats of agility. She can leap to great heights, though the maximum is unknown (vampires seem to be able to jump much higher).
The Slayer's running speed is also quite impressive, they can, at times, run as fast as a speeding car.
Resilience and Healing
A Slayer's body is substantially more durable and resistant to blunt force trauma than an ordinary human's. Slayers also have several times the endurance of a common human, so it is difficult, though not impossible, to bruise them, break their bones or strain their joints.
Despite these feats, the Slayer is far from invulnerable.
Slayers possess a heightened awareness of their surroundings. This heightened awareness could, with experience, allow the Slayer to know the position of an attacker and fight them blindfolded or in the dark. This is not a constant ability, however. This skill must be honed through practice and the Slayer usually must focus to achieve the full benefit.
All Slayers through the ages share a psychic link, manifested in dreams. A Slayer would frequently dream of herself as a Slayer in another time and place, even before being called. They could also experience prophetic dreams related to upcoming crises. Dreams existed in their own mystic plane or "dream space" where, for a Slayer, precognitive sense and the inherited memories of other Slayers could manifest themselves. One consequence of this power was that a Slayer has essentially fought all the battles of the Slayers before her. Also, Slayers have appeared in each other's dreams.
Potential Slayers have innate skills in combat, even before being called.
The Slayer's Watcher trains her to hone these talents, and to teach her specific fighting skills, such as various martial arts. The training helps her to battle the occasional demon whose physical strength outclasses her own. For most situations, however, her strength suffices. To test a Slayer's natural ingenuity and capability, the Watcher's Council administers a test known as "the Cruciamentum" if/when they turn eighteen, which striped the Slayer of her powers and forced her to fight a powerful vampire without them. It should be noted that the compound used to weaken the Slayer made her typically weaker than most normal humans. This rendered a Slayer who would still normally be physically fit without her powers remarkably feeble even for a human. This forces the Slayer to rely solely on her intellect and wit.
Overall, the Slayer's abilities seem to be enhancements of normal human attributes, rather than extra abilities garnered from a magical source.
The blood of the Slayer could be consumed by vampires to either strengthen themselves or to cure affliction. For instance, the Master used Buffy's blood to break himself free from his prison. Buffy also used her blood to cure Angel from the Killer of the Dead. Slayer's blood is also considered a powerful aphrodisiac.
Slayers are capable of being turned into vampires just as ordinary humans were, such is the case of Scarlett Scott-Thomas. The resulting "Slaypire" would have the combined strengths of both vampires and Slayers, but retain vampiric weaknesses.
Because the creation of a slaypire also calls a new Slayer, it is notable that there has been at least one incident where there were two Slayers before Buffy and Kendra's time.