Season 15 Callbacks

The final season of Supernatural has many returning characters, and callbacks to events of earlier seasons.

Returning Characters

• Amara
• Arthur Ketch
• Becky Rosen
• Benny Lafitte
• Chuck Shurley
• Eileen Leahy
• Jules
• Kevin Tran
• Rowena
• Sergei

Creatures and Spirits

• Constance Welch
• Demon Dean / Deanmon
• Evil!Sam
• John Wayne Gacy
• Lilith
• Mary Worthington
• Samifer

Spells and Weapons and more

• The soul catcher, a device Rowena used in 11.23 Alpha and Omega to collect souls and make the soul bomb to use against Amara, is used to capture the Hell ghosts.
• Rowena has to remove her resurrection charm that she has used twice before to cheat death.
• In 15.05 Proverbs 17:3, Dean and Sam pose as U.S. Wildlife Service "Agents Ford and Hamil" using the same fake IDs from 1.03 Dead in the Water. There is a running gag that Dean doesn't look like his picture anymore.
• Sam produces Ruby's knife to kill Lilith. Lilith remarks that he was only able to kill her in 4.22 Lucifer Rising because she let him.
• Sam uses a devil's trap bullet to trap Lilith, although it is unable to hold her.
• Dean uses a witch-killing bullet to to kill Emily the witch.
• Sam and Eileen find Rowena's Spellbooks which document everything she knows about magic. These journals have only made brief cameos in previous seasons before 15.06 Golden Time. Sam completes and uses an unfinished resurrection spell Rowena originally planned to use for Mary to revive Eileen.
• The voodoo doll created by Emily and her mother to torture Sam appears similar to the Twigs & Twine Doll created by Miss Beverly in 12.20 Twigs & Twine & Tasha Banes.

References to past events

• Dean speculates that Chuck's actions may have unlocked Lucifer's Cage and freed Michael where he was trapped at the end of 5.22 Swan Song.
• Belphegor refers to Dean's time in Hell as a torturer under Alastair.
• Confronted with John Wayne Gacy's ghost, Sam has to face his fear of clowns.
• We Got Work to Do - In 15.01 Back and to the Future, Sam says it and closes the trunk, while the image briefly flashes to the Winchesters closing the trunk at the end of 1.01 Pilot.
• Ketch and Rowena refer to their previous meeting, when the British Men of Letters captured Rowena several years prior and during her interrogation Ketch discovered that she implanted a special charm that could revive her if she is ever killed. In exchange for her release, Ketch made a deal with her to have the same charm implanted in his body, which he later used when he was killed by Mary Winchester.
• Francis Tumblety attempted to absorbed Kevin Tran's spirit, the last time this act among ghosts had been seen was with Whitman Van Ness in 7.19 Of Grave Importance.
• Ketch's alias "Mr. Blackmore" in 15.03 The Rupture is possibly a reference to Elizabeth Blackmore who portrayed Lady Antonia Bevell.
• Lilith is mentioned when her method of controlling demons working on Earth is explained via her crook, which offers a way to stop the "ghostpocalypse."
• Belphegor's plan to take in a vast number of souls so their power would make him invincible and God-like recalls Castiel actions in opening the portal to Purgatory and absorbing the souls there. This gave him great power and he proclaimed himself God.
• Rowena's sacrifice in 15.03 The Rupture is similar to both Sam's in 5.22 Swan Song and Crowley's in 12.23 All Along the Watchtower. Her last words, "goodbye, boys," mirrors Crowley's own "bye, boys."
• In 15.04 Atomic Monsters, Sam's nightmare is of a world where he embraced the demon blood and went full Dark Side. It's revealed that he had killed Bobby and Jody and is the leader of a demon army, as Azazel intended in 2.21 All Hell Breaks Loose: Part One. When he kills Dean with his psychic powers, his eyes go black as they did when he killed Lilith in 4.22 Lucifer Rising.
• In 15.04 Atomic Monsters, Becky Rosen references the plot to 7.08 Season Seven, Time for a Wedding! in which she drugged Sam with a love potion and married him in Las Vegas.
• Chuck typing the story on Becky's computer at the end of 15.04 Atomic Monsters is reminiscent of the ending of 9.18 Meta Fiction when Metatron is typing more recent events in the form of a story on his typewriter. Both characters also talk about knowing the end of the story and working out how they get there.
• In 15.05 Proverbs 17:3, in Sam's nightmare, Dean attempts to kill the Lucifer-possessed Sam with the Colt, only to have Lucifer heal the injury and burn Dean alive. This references both when Dean tried to kill Lucifer, possessing Nick, in 5.10 Abandon All Hope... and similarly failed, and when his 2014 self tried to kill the 2014 Lucifer with the Colt while he was possessing Sam in 5.04 The End. The nightmare Lucifer even wears the same white suit from the latter instance.
• While Dean catches up with Lee Webb, he mentions how he suffered from Ghost sickness at the hands of the buruburu Luther Garland in 4.06 Yellow Fever.
• Dean and Lee Webb were hunting buddies while Sam was in Palo Alto attending college at Stanford.
• Dean sings karaoke in 15.07 Last Call, which is a reference to singing karaoke in 10.01 Black during his demonic misadventures with Crowley. Dean even wears the same clothes on both occasions.

Meta references

Detail of Becky's Supernatural merchandise

• The name on the crypt that Sam, Dean, and Castiel take refuge in is "Carver," a reference to previous Supernatural writer and showrunner, Jeremy Carver.
• In 15.04 Atomic Monsters, we find Becky is still a Supernatural fan, writing fanfic and making miniatures. The Supernatural merchandise in Becky's house was a combination of commercial Supernatural merchandise, items made by fans, and some things made for the show. The plaid quilt and other sewn items were made by Stef, aka @arachnobite, who also made Jensen's Red Hood and Batman costumes. A carved Supernatural-themed chess set in the living room was gifted to Jared at EyeCon in September 2008 by by Sandra Echeverri (@Sanpao19).
  
• Becky's notes about Chuck's new manuscript can be seen as a meta commentary on the episode itself. Many of her notes such as there being no classic rock and neither Sam nor Dean mentioning Castiel and a cornered Sam and Dean listening to the "villain's" monologue happen in the episode. Her claims that the story has low stakes cause Chuck to write a new dark ending, which is mirrored in the episode when he disintegrates Becky and her husband.
• In 15.07 Last Call, Lee Webb quips that Dean can't just lip-sync to "Eye of the Tiger" when no one's watching. This is a reference to the Jensen Sings outtake for 4.06 Yellow Fever where Jensen Ackles lip-syncs to "Eye of the Tiger."