The story of Michael Myers terrorizing the town of Haddonfield, Illinois, began when John Carpenter introduced the Shape in 1978's slasher film, Halloween. The story's remained pretty consistent through the years as Michael stalks and murders sexy young adults -- most often in pursuit of Laurie Strode and her family -- and despite many lethal blows by the end of the films, Michael always returns in the next film to exact his vengeance. Very few Halloween movies deviate from the slasher film formula. However, the sixth film in the franchise, Halloween VI: The Curse of Michael Myers, reveals Michael's immortality comes from the demon Thorn, a supernatural entity who bestows dark powers upon those it possesses.
The film opens with a group known as the Cult of Thorn kidnapping Michael and Jamie Lloyd, the daughter of Michael's sister Laurie, and keeping them in captivity for six years. On October 30, 1995, Jamie gives birth to her son, and along with her child, escapes the cult with the help of a young midwife. Pursued by Michael, Jamie steals a truck and attempts to contact a local radio station, hoping to reach Dr. Samuel Loomis, though the attempt fails when the DJs ignore her pleas for help. Jamie hides her son at the bus station, but is chased and eventually killed by Michael.
In Haddonfield, Tommy Doyle, whom Laurie babysat in the first Halloween movie, is a recluse determined to uncover the truth behind Michael, while he spies on the current generation of Strodes living in the Myers' house, including Kara and her young son Danny. On the night of Jamie's escape, Tommy hears her on the radio and recovers her son from the bus station, naming him Steven. Meanwhile, Michael returns to Haddonfield and stalks and murders the Strode family. Kara and Danny seek protection with Tommy, who reveals he believes Michael is inflicted with the Curse of Thorn, giving him his unnatural abilities.
Tommy tells Kara and Danny that the druids making up the Cult of Thorn placed a curse on a child from their tribe, currently Michael, to protect themselves from the demonic spread of illness and death. The demon Thorn possesses the child, granting them superhuman abilities, and forces them to kill their entire family on the night of Samhain, or Halloween. Tommy believes Steven will be Michael's final sacrifice, while the Curse of Thorn passes to Kara's son Danny.
By the end of the movie, Michael kills all of Kara's friends and family and she, Danny and Steven are kidnapped by the cult. Dr. Loomis confronts his friend, Terence Wynn, after he reveals he's been working with the cult to study the power of Thorn and learn how to control it. Wynn implies that Steven is the successful result of experiments to clone Michael's pure evil, and that Kara and Danny will also be experimented on. Tommy frees Kara, and the two are pursued through the facility by Michael, who turns against Wynn and the other doctors and brutally murders them. After beating Michael with a lead bar, Kara and Tommy escape with the children. The film ends with a close-up of Michael's iconic mask while Loomis screams in the background, implying that Michael once again survived the attack.
The Curse of Thorn explains why Michael is so intent on killing every member of the Strode family and can be traced back to his original killing of his sister, Judith, the famous event that kickstarted the Halloween franchise. While most of the movies in the Halloween series follow the same format, The Curse of Michael Myers expanded on the franchise's established lore by introducing a darker and more supernatural power behind the Shape. While the proceeding films in the series ignore this new continuity and it is no longer cannon, it was an interesting exploration of what motivates Michael Myers, and the true darkness that lingers behind the mask.