Samhain (Supernatural)

In a small town in America, two witches were preparing a spell to summon the ancient demon Samhain, whose name is the original Halloween festival on 31st October. Samhain was in fact a demon, originally a human who had done some evil deed and been banished to Hell. However, he had control over the Undead, and could bring forth all manner of monsters.

Samhain was being prepared for freedom by the two witches, and Michael sent down two angels, Castiel and Uriel to deal with the problem, under the pretense that the angels did not want Lucifer free. In fact, summoning Samhain was one of the 66 Seals needed to free Lucifer. So, the witches were preparing to free Lucifer. The Winchesters persuaded a warmongering Uriel not to destroy the town but to spare the people in it when they fought the witch. However, the witch turned out to be a cheerleader named Tracy Davis, who was apparently sacrificing her teacher, Don Harding, and the brothers intervened to save Don, before Don turned on them revealing himself to be a witch to. However, Tracy snapped Don's neck. Tracy then freed Samhain, and she had Samhain possess Don. Don's corpse rose and greeted her, but then called her a "whore" and killed her.

Proceeding to the cemetery where a Halloween party was, Samhain used Don's body to fool the students and lock the gates on them, then summoned zombies. He killed one or two children but the brothers opened the gates and saved the others. Dean then fought all the Undead creatures that came forth, and Samhain appeared, challenging Dean. Dean battled Samhain and he eventually was challenged by Sam, who used his demonic powers to exorcise the demon and send Samhain bursting out of Don's mouth, which made Samhain go back to Hell.