Siren

Sirens were a supernatural species who were originally psychic, and given immortality that depended on the feeding of human flesh to remain young and beautiful. They were the servants of Arcadius who were tasked with harvesting the souls of the wicked. They were one of the oldest supernatural races and there were only two known in existence.

Creation
Sirens came into creation when Seline struck a deal with Arcadius to save her dying sister, Sybil. The exact details on how he was able to accomplish this remains elusive, but Seline mentions that one needs to consent first to be transformed. Consent can also be given if the subject is dead, as according to Sybil who died prior to the deal, Arcadius could see into her soul and see her desire to live. In return for immortality, Seline and her sister would have to constantly devour the flesh of anyone who has committed a bad deed, no matter how small or insignificant. They predate the vampire species by approximately two millennia, making them one of the oldest supernatural species in existence. Sybil claims to be over three thousand years old, making Sirens older than the immortals, Silas and Amara, by at least a thousand years. The sirens eventually became known in human folklore with the story varying on information.

The Capture of the Sirens
On June 21st, 1790, both Seline and Sybil were lured through the underground tunnel system of (the not yet founded) Mystic Falls, by Beatrice Bennett and Ethan Maxwell into the Amory's Vault after their successful plan to destroy the local coven. There, Beatrice entrapped them with a spell.

The Release of Seline
Nearly a hundred years later during 1883, Virginia's great-grandfather, Dalton St. John released Seline from the Armory's Vault, presumably by accident, when the vault was re-opened by him and his team in 1882. It is unknown as to why Sybil did not leave along with her.

The Release of Sybil
Bonnie broke her cousin's spell that sealed the Armory's Vault when forced by Alexandria St. John. Quickly thereafter, all Armory members were killed by Sybil, though Bonnie re-sealed the Armory to prevent the evil presence from being released. Though in order for Damon to get to the last member of the Eight Everlastings and save Bonnie, the siphoner twins, Lizzie and Josie, removed Bonnie's spell. The Siren therein used Elena's voice to lure Damon further into the vault and eventually subdues him with her mind control. Enzo enters the vault soon after and is confronted by Damon. After a short conversation, Enzo is grabbed from behind by the monster. The Siren and the two vampires managed to find a way out of the Vault, and the Siren forced the two vampires to bring it 'evil' victims. Later the Siren, Sybil, finally consumed enough people to have recovered enough of her strength and is rejuvenated, regaining her beauty.

Present Day
Sybil had become frustrated at both Damon and Enzo for their resistance to her and sought to remove whatever they were holding onto. In Damon's case, she replaced his memory of Elena and Bonnie with her. With Enzo, she sought to kill Bonnie and succeeded in killing Sarah Nelson.

Sybil later managed to gain Damon's full loyalty and attempted to "kill" Enzo for escaping her. Sybil later schemes with Damon, who has taken charge to make an alternate deal with Arcadius after being reunited with Seline and listening to her plan, which involved offering Alaric's twins to Arcadius. Sybil and Damon's plan was to instead offer himself and his brother as replacements. Sybil later tells Seline that in revenge for what the latter did, Sybil made a side deal to keep her powers and to cut Seline from it altogether, but ominously tells her that her plan is not done yet.

Following Seline being abdicated from Arcadius' service, both Sybil and Seline begun looking for the pieces of the Mystic Falls Founders Bell. While Sybil apparently wished to collect the pieces in an effort to ascertain the only weapon capable of killing her, Seline wanted the bell in the hopes of using it to kill Sybil. With aid from Dorian Williams and Matt Donovan, Seline managed to assemble the bell and, with Stefan's aid, nearly succeeded in releasing hellfire, thereby killing Sybil and all those in Mystic Falls. Ultimately failing in her plan, Seline and Sybil meet, in hopes of reconciliation. After failing to make amends, Arcadius reveals himself and informs them that while the bell did not release hellfire, it was rung enough for him to pay a visit to the world of the living. Deciding to take matters into his own hands, Arcadius destroys Seline and Sybil with hellfire.

Powers and Abilities

 * Super Strength: Sirens possess vast strength. Sybil was strong enough to kill various members of The Armory as well as overpower Damon and Enzo long enough to enslave them. It is unknown if sirens are stronger or weaker than Original vampires nor has it been shown that they possess such strength in their normal/human form. Sybil was able to kill a police man, who was not under her control, with her bare hands through the use of her claws, implying she still possesses some form of enhanced strength to overpower a large adult male.
 * Super Speed: Sirens are incredibly fast, this was seen when Sybil evaded The Armory's men that were searching for her. She again demonstrated her speed further when she dragged Enzo into the shadows of the Armory even at a desiccated state. Such speed has not been used since.
 * Super Durability: As an immortal being, sirens are indestructible, though despite this, their actual durability seems to be less effective than immortals. Sybil was knocked unconscious simply by going through a windshield. Later Caroline, a young vampire, knocked her out with a just kick to the head, though this was after the Staff of Arcadius was used against her.


 * Immortality: Sirens cannot die due to the deal they made with Arcadius and can remain youthful so long as they continue to feast on the flesh of humans. Virginia mentions that the only known siren has lived for thousands of years. Sybil later says she is immortal and is over three thousand years old. This form of immortality, however, is dependent on Arcadius and, upon a temporary death, he sends their spirit back into their body, effectively reviving them.
 * Accelerated Healing: Sirens are able to regenerate from damage sustained on their bodies and appear to be superior to even the likes of an Original vampire. Sybil was shown to heal near instantaneously from a snapped neck, however, she was unable to rapidly heal wounds sustained from being forced through a windshield and had to wait for a passing car, implying that healing may be dependent on feeding.
 * Telepathy: Sirens, seemingly from their previous psychic heritage, can enter into the minds of another person to read their thoughts and access their memories. This was initially done using their voice as a guide, but has since been refined into singing. They can strengthen this with physical contact, allowing them to search the entire mind of their victims and even alter their memories. This ability is superior to a vampire's as they don't require eye or even physical contact, but the ability is seemingly inferior to an Immortal's given the resistance some can have to it. Sirens are capable of telepathic communication even from a great distance as Damon was contacted by Sybil from within the Armory while he was driving at an unknown distance away.
 * Mind Control: Sirens can take over the minds of their victims, even to the point of shutting them down. The victims are conscious of this interaction as it creates a psychic rapport between siren and servant. This allows them to maintain a constant presence from within such that servants straying too far from Sybil will be struck with psychic pain and suffer hemorrhages until they return to her. By using their "Siren Call", mind control can be used en masse and has even be used via cellphone service to access and reestablish the psychic connection. However, some vampires, like Damon and Enzo, can offer some resistance to a siren's access by focusing on the people they care most about. They can also use their mind control to force a vampire to turn on/off their humanity; the former being a painful process as the flood of memories can crush them under the weight of their guilt.
 * Memory Manipulation: Sirens possess the ability to manipulate and change the memories of the victims under their control. Sybil has shown the ability to manipulate Damon Salvatore's memory and alter one key memory; of his first meeting with Elena, where she inserted herself and erased Elena. Subsequently, she had to alter individual, "key" memories to continue to change their personality. Seline has also been showing erasing Stefan Salvatore's memory, altering his subconscious enough that he forgot the time when he massacred an entire village in Monterey on Christmas Eve.
 * Psychic Pain Infliction: Sirens are able to induce extreme amount of pain through their telepathic powers. Sybil was able use this technique on Enzo, which was strong enough to manifest physical symptoms, such as coughing up blood and nose bleeds, while being separated great distances and maintaining normal appearances.
 * Psychic Illusions: Derived from their mind control, Sirens can create minor illusions, forcing their victims to see what they want. However, this has only been demonstrated on a human and Seline's illusion was broken after Lizzie siphoned from Sybil, breaking her concentration.


 * Voice Manipulation: Sirens are able to manipulate their voice to lure their victims as fabled. Sybil has shown to use her voice to captivate others through singing and mimic the voices of others like Yvette St. John and Elena Gilbert. Their control is so fine that they are able to generate sound waves to match the resonant frequency of glass in order to break it. Sybil demonstrated this when she used it to break the glass and free herself from the Armory.


 * Claws: Sirens possess sharp claws and can use them to inflict fatal wounds onto humans; their claws have only manifested when severely deprived of food or when their power had been siphoned. It is unknown if they can manifest them willingly.
 * Aquatic Respiration: Sirens appear to have some form of underwater adaptation. Sybil spent many months underwater, suggesting that she is able to breathe underwater and also they have the ability to transform their legs into a fish tail which can help them in vast waters to swim.

Weaknesses

 * Arcadius: As the creator of the sirens and the one who gave them their immortality, he has the power to take away their immortality and kill them with his own Hellfire. Their speed of recovery from an otherwise fatal attack is also dependent on him, as Sybil's revival was delayed once as Arcadius held a conversation with her, prior to her soul being sent back to her body.
 * Hunger: Sirens feed on the flesh of humans which they require in order to maintain their youth and strength. Sirens also appear to require much more sustenance than vampires to be able to restore themselves if they haven't fed in centuries. Abstaining from such causes them to deteriorate to some degree, as seen with Sybil's hands after being released from the vault. Sybil also claimed that her eyeballs had rotted away over time whereas Damon mentioned that Sybil's face rotted off.
 * Magic: Sirens appear to be susceptible to the powers of witchcraft seeing as the Bennett witches were able to imprison them with various spells. It has been confirmed that a siphoner can siphon the magic from sirens.
 * Mystic Falls Founders Bell: An indestructible bell that amplifies the effects of the Staff of Arcadius, an ancient Mesopotamian tuning fork, when combined with the Maxwell Striker. When struck, it produces an unknown frequency that disrupts and neutralizes psychic activity, and is capable of stunning sirens in the process. Other than Arcadius, this bell is the only known weapon capable of killing sirens. This, however, is dependent on the release of Hellfire when struck 12 times by someone from the Maxwell bloodline.