Frequent returning characters include hunter Bobby Singer (who becomes a father figure to Sam and Dean after season two), Castiel (an angel), Crowley (a demon and the King of Hell), and Jack Kline (the Nephilim).
Abaddon goes back on her agreement and ends up mortally wounding Henry, but not before he shoots her in the head with a bullet engraved with a devil's trap, binding her powers and her to her now-paralyzed host body.
Appearing in Crowley's former palace, Asmodeus announces himself as the new King of Hell to all of the gathered demons with a stated intention to rule until Lucifer or his Nephilim son Jack can be found to replace him.
The Winchesters come to the funeral of one of Duke's victims, their father's favorite wrestler and stumble across the crime scene of his newest target, quickly putting together that they are dealing with a demon stealing souls.
A recent meeting with the alternate reality version of the archangel Michael has caused Kip to reevaluate his life and decide that he wants everything and he has begun attempting to take up the position of King of Hell.
Dean expressed skepticism initially (due to hearing the story in the midst of a drinking game inspired by the exploit) but he later confided to Sam that he believed Asa to be a 'legit' hunter, evidenced by his armory, complete with an angel blade.
After a violent encounter with them, Charlie is shot but narrowly escapes, and calls the Winchesters from a telephone booth, informing them of her discovery and injury, mentioning she sewed it back together with dental floss, a testament to her resourcefulness.
Donna burns the mask and it appears to be over, but a young woman in a court jester's outfit attacks the local football coach and the Winchesters learn that they are dealing with an angry ghost, not a cursed object.
Mary helps defend Bobby's colony against an angel attack led by Zachariah and together with Jack, forms a resistance against Michael as learned by Dean and a resurrected Arthur Ketch when they briefly visit Apocalypse World in "Bring 'em Back Alive".
A case he worked during his year spent hunting with Sam is seen in the episode, "Unforgiven", during which Samuel was shown to be disturbed at soulless-Sam's actions, using one of their current allies as bait to trap a monster.
In "Hey, That's No Way To Say Goodbye," Samuel returns after receiving the news that Ada has found magic capable of stopping the Akrida Queen who intends to use a planetary alignment to open her portal and begin the invasion.
Samuel is contacted by a former hunter named Joan Hopkins who turns out to be the Akrida Queen, having been driven insane, consumed monster essences and seeks to wipe out humanity as a result.
After the Winchesters open a rift to Apocalypse World, Arthur decides to join Dean on the mission, feeling that he is safer in another universe when Asmodeus will inevitably come looking for him.
With the rift closing, Arthur chooses to remain behind in Apocalypse World with Charlie to continue the mission to find Mary and Jack and to help coordinate for Dean's inevitable return with reinforcements.
Through the connection that still exists between them, Dark Kaia has learned of her world's peril and is frustrated when the Winchesters refuse to use Jack's powers to open the rift as it risks drawing God's attention.
It is shown in "Trial and Error" that Kevin lets himself go completely while he focuses on translating the tablet, believing that closing the gates of Hell will be the only way he can go back to a normal life.
In the third-season episode "The Kids Are Alright", Dean decides to visit Lisa and he discovers she has an eight-year-old son named Ben who shares his cocky attitude and love of classic rock.
In "Season 12, Mamma Mia", Mick comes to America to return Toni Bevell to London, where she'll face consequences after establishing that she's gone way off her original mission, which was to identify American hunters and gain their trust.
After Claire Novak is bitten, Mick advocates killing her while Sam wants to try a cure the British Men of Letters invented involving injecting the newly turned werewolf with the blood of their sire.
In season 5's "Sympathy for the Devil", Nick, who has recently lost his wife Sarah and son Teddy in a brutal home invasion, is tormented by visions created by Lucifer regarding the loss of his family.
Though Ms. Watt suggests bringing in Mr. Ketch, Toni refuses as she doesn't like the man and instead decides to resort to mental torture, causing Sam to have hallucinations of dead people in an attempt to break his mind.
Following the accidental death of Renny at the hands of Eileen Leahy and the Colt, Doctor Hess personally comes to the British Men of Letters compound, leaving Britain for apparently the first time.
Chuck Shurley, also known by the pseudonym Carver Edlund and portrayed by Rob Benedict, is an author of a marginalized book series Supernatural, which recounts everything the Winchester brothers have experienced during the show's run.
As Dean brings Jack, who is intended to be a bomb, to the bunker, Sam arrives, revealing that their plan will result in Billie, the current "death", to take Chuck's place.
In season three, Sam and Dean encounter Madge and Edward Carrigan (portrayed by Merrilyn Gann and Spencer Garrett) in "A Very Supernatural Christmas" where they are pagan gods of the winter solstice from an unspecified culture.
In season ten, Sam and Dean encounter Calliope (portrayed by Hannah Levien) in "Fan Fiction" where she was interfering with a play adapted from Chuck Shurley's book by manifesting a copy of the Vanir's scarecrow form.
At the end of season 14, God opens every door in Hell and unleashes billions of condemned souls upon the world, some being old enemies of the Winchesters like Constance Welch, Mary Worthington, and John Wayne Gacy.
Nothing worked, until a Borax cleaning product used by Sheriff Jody Mills upstairs dripped from the ceiling; the chemical was significantly more painful and corrosive than anything else used, which Bobby affirmed to be the most effective countermeasure to Leviathans, in tandem with decapitation as long as the head was kept away from the body.
Originally they believe the wife to be a ghost and salt and burn her body, but discover more murders of people by deceased loved ones, all connected to a grief counselor named Mia Vallens whose patients are closed-lipped about how she helps them achieve peace.
In season 12's "Somewhere Between Heaven and Hell", a wraith is amongst the monsters Dean kills with a wire-wrapped baseball bat while on a hunt assigned in secret by British Men of Letters operative Mick Davies.