Personality and appearanceEdit
Mary was born as Mary Archer, one of the two daughters of a happily married couple living in a cottage near Sleepy Hollow. When Mary was still a little girl, her father unexpectedly died for some unknown reason, and the family's landlord Sir Peter Van Garrett, evicted them and sold their home to the Van Tassel family. Due to Mary's mother being suspected of doing witchcraft, no one in the town was willing to take the Archers in, so the Archers took refuge in the Western Woods. Mary's mother later died within a year afterward, forcing Mary and her sister to scrounge for themselves in the Western Woods. One day, while gathering firewood, Mary and her sister ran into the bloodthirsty Hessian hiding from the arriving American soldiers. Despite the Hessian's order to be quiet, Mary gave him away to his pursuers by snapping a stick into two while her sister ran away in fear. While watching the Hessian's execution and burial by the hands of the soldiers, Mary made a pact with the Devil: in return for her soul, she would be allowed her to raise the Hessian from the grave to assist her in taking revenge on the Van Garretts and Van Tassels.
18 years later, Mary came over to the Van Tassels' residence as a sick-nurse for Baltus' first wife Elizabeth, whom she secretly poisoned before proceeding to enter a relationship with Baltus and becoming his second wife. Two years later, she heads over to the Tree of the Dead, where the Hessian's grave is marked at. She then digs the grave and stole the skull herself, intending to use her dark magic to revive the Horseman under her control to kill those who have wronged her. As New York police constable Ichabod Crane arrives to Sleepy Hollow following the murders of Sir Van Garrett, his son Dirk, and the widow Emily Winship, Lady Van Tassel pretends to be supportive with him. As the investigation goes on following the murders of Jonathan Masbath and Magistrate Samuel Phillipse, Crane follows the clues through the woods to a crone witch, who gives him directions to the Tree of the Dead where the Horseman's grave is located. After seeing that the skull has been stolen and witnessing the murders of the Killian family and Ichabod starts to believe that a conspiracy links all the deaths together, deducing that all who knew about Van Garrett's new will were the victims of the Horseman (except for Brom, who was only killed in self-defense). Crane then suspects that Baltus is the person behind the murder spree since he is the only one who would have inherited the fortune, though Katrina refuses to believe that her father would do such horrible things. One night, Crane and Masbath's son see a mysterious cloaked figure holding a lantern, disappearing into the Western Woods. As young Masbath stays behind while Crane goes to investigate, not only does he discover the cloaked figure to be Lady Van Tassel, but that she's engaged in a sexual encounter with Reverend Steenwyck, during which, she grabs a knife and violently slices the palm of her hand, allowing Reverend Steenwyck to lick her wound clean. The morning after the encounter, Lady Van Tassel notices how Crane has been so careful not to look at her hand or ask how she cut it, which would have been polite of him. She tells Crane that she knows that he had followed her into the woods and makes him promise not to tell her husband about her encounter in the woods. While gathering out flowers, Baltus witnessed the Horseman coming towards Lady Van Tassel with his sword unsheathed, and heads off to the church, with the townspeople filing in just as the he arrives. With the men firing muskets as the Horseman circles the church, Crane realizes the Horseman can't enter the church grounds due to some protective supernatural force. A massive fight breaks out in the church when Dr. Thomas Lancaster is about to confess his role behind the conspiracy, only to be killed by Reverend Steenwyck, who is in turn shot to death by a frightened Baltus. The chaos ends only when the Horseman harpoons Baltus through a church window using a pointed church fence post attached to a rope, dragging him out and acquiring his head.
As Crane is about to leave Sleepy Hollow in disgrace, he becomes suspicious when the hand of the corpse of Lady Van Tassel has a wound which shows signs of having been caused post-mortem, since it was made when the woman was already dead. His suspicions are confirmed to be right when the real Lady Van Tassel emerges, alive, from the dark and shocks her step-daughter Katrina into a faint. Lady Van Tassel summons the Horseman again, this time to kill Katrina to secure her hold of the Van Tassel fortune to herself. As Katrina awakens, Lady Van Tassel confesses to her about her backstory and her true role behind the murder spree, also admitting that she killed Katrina's mother Elizabeth when posing as her sick-nurse. She also confessed that she had the town's four elders under her thumb to be drawn into her plot; blackmailing Notary James Hardenbrook (who committed suicide before Baltus' death) and Magistrate Phillipse, silencing Dr. Lancaster to cover his affairs with the Van Tassels' servant Sarah (whom Lady Van Tassel killed to fake her death), and corrupting Reverend Steenwyck with his lust for her. She also confessed to having recently killed the crone witch (who is revealed to be her estranged sister) for helping Crane and young Masbath in finding the Hessian's grave. After confessing her crimes, Lady Van Tassel states that she now plans to have Katrina killed by the Horseman so she can get the entire fortune under her fist. Fortunately, Crane and young Masbath arrive to rescue Katrina and they head to the Western Woods to evade the arriving Horseman. However, Lady Van Tassel arrives by horseback and shoots Crane while holding Katrina violently by the hair, awaiting for the Horseman to come and kill her. However, Crane (managing to deflect the shot with Katrina's magic book inside his coat) manages to get the stolen skull while young Masbath knocks out Lady Van Tassel with a large branch. Crane then returns the skull to the Horseman, reverting his head back to its normal form. Finally freed from Lady Van Tassel's grasp, the Horseman spares Ichabod, Katrina, and young Masbath while reuniting with his horse Daredevil. Recognizing Lady Van Tassel as the little girl who betrayed him to his death years ago, the angry Horseman hoists the evil witch up on horseback and gives her a bloody kiss with his sharp teeth, much to her complete distraught. The Horseman and Daredevil then gallop on their way back to Hell, taking a screaming Lady Van Tassel with them to make her pay for her crimes and fulfill her side of the deal with the Devil.