Season 12. Dean is both overjoyed and shocked to see his mother again, while Mary is confused and initially unaware who Dean is, since she remembers him as a 4-year-old boy. Mary attacks him and Dean is forced to reveal to Mary that she has been dead for 33 years, and that he is indeed her son.
The Yellow-Eyed Demon shows Sam a vision of the night Mary died. It is revealed that she was killed because she interrupted the demon as he fed his blood to baby Sam. Sam learns for the first time that he was fed demon blood, and that Mary knew the demon that killed her.
Dean is barely holding it together. He doesn't like that Jack is calling Mary's death, “the accident.” But he plays along and says they understand and they forgive Jack. Sam asks if that's what Jack wants.
Seeing that Dean was hesitating, he bursts in and Emma turns to face him, flashing him her red eyes before turning to Dean and pleading for his help. However, as she turns again to face Sam, he shoots her in the chest, killing her.
Emma Winchester is the daughter of Dean Winchester and Lydia. She is an Amazon warrior, trained to kill her father, but she refuse to go through it and was accepted by her family. She is very close to Cassandra.
Jack begins hallucinating Lucifer talking to him. At the same time, the Winchesters discover Nick's body and learn from Rowena that Mary is dead, accidentally killed by Jack's outburst.
Targeted by Azazel, retired hunter Mary had the distinction of being the first character to meet her maker. The Yellow-Eyed Demon pinned Mary to the ceiling of baby Sam's room, slit her stomach, and eventually set her ablaze. Mary's gruesome demise forever scarred the Winchesters.
As long-term viewers know, Mary was eventually resurrected in Season 12, and while she initially struggled to accept three decades' worth of change, she proved to be a skilled hunter herself, working alongside her sons to prevent hell on earth.
When Dean died, he left Sam alone, and he hasn't quite forgiven himself for that. Though we know that Sam is okay (he eventually marries and has a son, whom he names Dean in honor of his late brother), Dean is still the over-protective big brother he's always been.
Azazel eventually comes across Mary Campbell, the future mother of series protagonists Sam and Dean Winchester. After taking possession of her father (Mitch Pileggi), he kills her mother and stabs himself to kill his host. Mary's fiance, John Winchester, is the demon's next victim.
When Jack killed Mary Winchester, he sought to redeem himself by creating new angels but it didn't help and he was locked away by the Winchesters. Jack escaped and roamed Earth before he was confronted by the Winchesters who intended to kill him but stopped.
Lydia is an Amazon who hooked up with Dean Winchester at a bar and the two made love in bed. She was impregnated by the older Winchester and in just a few hours, she was pregnant with her unborn child.
Emma finds Dean, telling him she is running away from the Amazons, but actually intending to kill him. When Dean hesitates, suggesting she could actually leave them, Sam arrives and shoots her.
Background. Sam is Mary's second-born son. Mary was murdered in his nursery by Azazel on the night of his 6-month birthday. Before the demon killed her, Mary recognized him from the deal she made a decade ago and realized what was occurring.
Before dying, John tells Dean, if he can't save Sam, he'll have to kill him, should he become evil. The fourth season episode "On the Head of a Pin" reveals that the demon Alastair tortured John in Hell for over a century, with John refusing the demon's offer to stop if he himself would torture someone else.
He starts to smash the mirrors around the room, but he begins to bleed from his eyes, and his reflection addresses him, saying that he truly is to blame for Jess' death because he had nightmares about her demise for weeks prior to it happening, but did not try to save her.
The demon, Azazel, became fascinated with Mary and later killed both her parents. After also killing John, Azazel promised to resurrect him in exchange for permission to enter Mary's house in 10 years.
He later goes on a suicide mission, stating that he would rather die than watch Dean crumble and fail. Dean appears visibly saddened by Castiel's lack of faith in him. Castiel later returns in Two Minutes to Midnight and apologizes to Dean for not having more faith in him. Dean forgives Cass, and they reconcile.
The group entered Dean's mind to get him to eject the Archangel. A fight broke out and Dean ended up trapping Michael within his subconscious, while causing his monster army to scatter.
Michael explains how when he possessed Dean, he wouldn't stop fighting back, so he left an opening in Dean's mind to possess him again without permission. He needed to break Dean, in order to keep him suppressed for good in his mind.
Castiel is a young Seraphim, former leader of his garrison, and youngest angel in all of Heaven. He is the husband of the demoness, Meg Master and widowed father of his daughter, Cassandra Masters.
Millicent "Millie" Winchester is the second child of John Winchester and Mary Campbell, the younger sister of Dean Winchester, and the older sister of Sam Winchester. She is named after John's mother, Millie Winchester. She is the mother of Maury Winchester (Nobah Dee).
Adam Millagan is a supporting character in Supernatural. He is the younger half-brother of Sam and Dean Winchester and the son of John Winchester. He appears as a minor character in season 4 and a supporting character in seasons 5 and 15. He also serves as the primary vessel for the Archangel Michael.