|Powers and Abilities||Super strength, regeneration, possession, shapeshifting.|
|Vulnerabilities||Borax, beheading and powerful spells can temporary incapacitate them. Blood of the fallen, being eaten by another leviathan and "bibbing" can kill them.|
|Appearance||Black goo, or human with the ability to transform its face into a giant mouth with pointed teeth and bifurcated tongue.|
|Episode(s)|| 7.01 Meet the New Boss|
7.02 Hello, Cruel World
7.03 The Girl Next Door
7.05 Shut Up, Dr. Phil
7.06 Slash Fiction
7.09 How to Win Friends and Influence Monsters
7.10 Death's Door
7.11 Adventures in Babysitting
7.12 Time After Time
7.16 Out with the Old
7.20 The Girl with the Dungeons and Dragons Tattoo
7.21 Reading Is Fundamental
7.22 There Will Be Blood
7.23 Survival of the Fittest
8.01 We Need to Talk About Kevin (mentioned)
8.05 Blood Brother
8.07 A Little Slice of Kevin
8.18 Freaks and Geeks (mentioned)
8.20 Pac-Man Fever (mentioned)
There are things much older than souls in Purgatory, and you gulped those in too... Long before God created angel or man he made the first beasts: the leviathans... I personally found them entertaining but He was concerned they'd chomp the entire Petri dish. So He locked them away. Why do you think He created Purgatory? To keep those clever, poisonous things out. Now Castiel has swallowed them, he's the one thin membrane between the old ones and your home.
Leviathan, also called the Old Ones, pre-date the creation of humans and angels, as well as the soul itself. They would also pre-date any beings with souls, such as monsters. They are therefore among the first creations of God.
Death describes them as immensely powerful, hungry, clever and poisonous. Before God went on to create more creatures, however, He felt that the Leviathans threatened to consume and destroy everything "in God's Petri dish." For this reason, Death states that God created Purgatory and sealed the leviathans inside to contain them and their hunger.
When Castiel opened the door to Purgatory and took in the power of the souls stored there to increase his own angelic power, he also took in the leviathans. With the help of Sam, Dean and Bobby, Castiel finally expels the souls back to Purgatory, but some of the leviathans "held on." Castiel's vessel is taken over by the leviathans, and they manage to guide Castiel's vessel into a nearby water catchment just before the vessel disappears in a whirlpool, releasing them into the water supply.
The number of leviathans that escaped from Purgatory is unknown. The leviathans operate within a hierarchy lead by Dick Roman. Their 'modus operandi' is to take on the forms of humans who have valuable skills, or are in positions that may be useful, particularly positions of power including the military and corporations. Dick Roman says their golden rule is "there's no such thing as monsters." Their plan, as revealed by Bobby Singer, is to turn humanity into the perfect never-ending food-source. To accomplish this, they are building slaughterhouses for humanity in various locations and are putting an additive into the food that dumbs-down humans. It also kills all monsters that feed on humans such as vampires, werewolves and ghouls and the leviathans develop a version that they put in coffee creamers that breeds out unwanted traits and kills those with them. The leviathan plan is also to build centers to cure diseases so that their food supply will be disease free.
The Word of God tablet on the leviathans reveals the way to stop them:
"Cut off the head, and the body will flounder. Waste not thy time nor your breath upon the leviathan herd. Point thy blade at the heart of their master, for from him springs all their messages. Leviathan cannot be slain but by a bone of a righteous mortal, as light and good as the leviathan are hungry and dark, washed in the three bloods of the fallen: a fallen angel, the ruler of fallen humanity, and the father of fallen beasts."
Dean, Sam and Castiel use this to kill Dick Roman, and with him dead, the remaining leviathan cease to be a significant threat. By one year after Dick's death, their influence seems to be completely gone from the world as people are shown to be back to normal and Sam and Dean are able to eat normal food without apparent worry about the food additive.
Castiel and Dean, while trapped in Purgatory, are constantly hunted by leviathan. They appeared suddenly as a mass of black goo that lands, causing a crater in the earth, and morph into human form. With the help of Benny Lafitte they defeat at least four, but Castiel later tells Sam and Dean that his last memory of Purgatory is being hunted by leviathans.
In 8.20 Pac-Man Fever, Sam, Dean and Charlie Bradbury bring up a leviathan as possibly being what is killing people, indicating that there are still some leviathans unaccounted for though it turns out that they are not dealing with one.
The leviathan have been a metaphor for corporate greed, among other things, all season. When we were crafting these villains, we talked about what freaked us out in the writers’ room and we came to the conclusion that big corporations are scarier than the government.
A lot of our villains over the years have been monstrous, and we thought these monster corporations and their lack of morality seemed to be a perfect fit for this ultimate monster.
The leviathans have sharp teeth within an expanding jaw, and possess a bifurcated tongue. They feed on human internal organs - sometimes with cheese.
They can mimic a particular human being following contact with one, or if they obtain DNA from a person. They are then aware of all that person's thoughts and feelings, and even hallucinations. All the leviathans now outside Purgatory absorbed everything that Castiel knew, as he was their original vessel. When wounded they "bleed" black goo.
Leviathan!Sam said that he once had a brother with many issues, and that he ate him in the end - so they are not averse to cannibalism. This is later shown when Dick Roman eats Victor and George plans to eat Joyce Bicklebee, with George telling the Winchesters that a leviathan eating another is one of the only ways to kill them.
"Bibbing" was first mentioned by Dick Roman when he told Valente: "Next time, call me with a win. For your sake. Please don't make me bib you." When Dick decides that Dr. Gaines's experiments are drawing too much media attention, he decides to bib him. This involves literally placing a bib on him, and then Dr. Gaines eats himself until nothing is left - except a goo stained bib. This is one of the only known methods of eradicating a single leviathan for good.
Sam and Dean refer to them as "big mouths."
Powers and Abilities
- Possession - Leviathans can possess any human they come into contact with in their fluid form. This person becomes their physical embodiment of sorts. These shells bleed black ectoplasmic blood when injured and can reshape their jaws to display long sharp teeth and a two-pronged tongue.
- Shapeshifting - Once a vessel is taken they can reshape it into any human form they touch. They require only a fragment of DNA to transform into a person; even lost hair will do. The creature possessing a little girl takes the form of a doctor by touching his arm. They can also absorb the memories of anyone whose form they take, much like a shapeshifter, but without requiring the person to remain alive. It is revealed that certain humans like Charlie Bradbury and Bruce Springsteen possess a certain "spark" that means they cannot be emulated as effectively.
- Super strength - They are shown to possess greatly enhanced strength; at their first meeting, they are able to hurl Dean and Bobby across a room with little effort.
- Healing/Endurance - Leviathans are extremely resilient, surviving multiple shotgun blasts with silver shot, including one to the head at point blank range. One also survived and reassembled itself after being crushed by a falling car. They can even re-attach their heads if decapitated. 
- Can kill angels - Episode 7.21 Reading Is Fundamental shows that leviathans can overpower angels easily. They are immune to an angel's power and can kill them by forcing their fists into the angel's stomach, causing the angel to then ooze black goo and die.
- Flight - In Purgatory leviathans are able to fly through the air in the form of meteors of black ooze that crash into the ground and take on a humanoid form.
- Blood of the Fallen - The leviathan tablet states that a leviathan can be killed by a bone of a righteous mortal soaked in the blood of the fallen. There are three fallen whose blood is required; the first of these is a fallen angel (Castiel's blood qualifies). The other two fallen are the ruler of fallen humanity (meaning Crowley, the King of Hell) and a father of fallen beasts (an Alpha). Once this weapon is assembled, the leviathan only needs to be given a fatal blow to be killed, but it can result in those nearby being pulled to Purgatory with the leviathan soul.
- Borax - Leviathans are highly susceptible to materials that contain the chemical compound borax (sodium borate) such as household cleaning products. Contact with their skin results in an instant burning effect that can reduce them to charcoal-like husks if they are exposed to too much. It is suggested that they will eventually heal from the effects, however. Their leader, Dick Roman, may be less susceptible to the chemical.
- Beheading - Removing a leviathan's head disables them temporarily. But unless the head is kept far away from the body it will re-attach itself. The combination of burning them with borax and then beheading them and separating the head and the body appears to be the only way to put them down indefinitely, assuming the head has no way of finding its way back to the body.
- Witchcraft - Leviathans show susceptibility to witchcraft. It can incapacitate them temporarily.
- Other leviathans - Leviathans can be killed by another leviathan eating them. A leviathan can even eat itself, a process referred to as "bibbing."
- Rigid hierarchy - The leviathans rely heavily on having one all-powerful leader to give them instructions and conduct their master plan. If he dies, they fall apart completely and revert to a state of disorganization.
List of Leviathans
The first leviathan appearance is when they take over Castiel. As leviathans take the form of humans, they are referred to here by their human names.
- Dick Roman (deceased) - Leader of the leviathans.
- Annie / Dr. Gaines (deceased)
- Edgar (incapacitated) - A leviathan who works in demolitions.
- Two members of the Stockville Sharks Swim Team, who later become a head nurse and a hospital administrator at Sioux Falls General.
- Chet (incapacitated) - Leviathan who works for a credit card company assigned to track down Sam and Dean Winchester.
- Valente - A leviathan FBI agent.
- Leviathan!Sam and Leviathan!Dean (incapacitated) - Leviathan doppelgängers of Sam and Dean Winchester.
- Susan - Dick Roman's assistant.
- Joyce Bicklebee (deceased) - A leviathan in real estate.
- George - Joyce's assistant.
- Pete - Charlie Bradbury's manager at RRE.
- Tarrell - The leviathan who assumes Pete's position at RRE.
- Victor (deceased) - Roman's minion at RRE.
- Approximately ten leaders of various divisions of Dick Roman's grand plan.
- Three SucroCorp guards (incapacitated).
- At least one SucroCorp scientist (incapacitated).
- Four seen during Dean's time in Purgatory (incapacitated).
Whilst ingesting all the souls from Purgatory to became the new God, Castiel also took in the leviathans. The leviathans struggled for control, briefly taking over Castiel's vessel to smite people that even the now-wrathful Castiel didn't intend to, and causing his vessel to physically deteriorate and potentially explode.
With the assistance of Dean, Sam and Bobby, Castiel returns the souls to Purgatory. But "some" of the leviathans hold on, and assume control of Castiel's vessel. Stating that Castiel is dead, the Leviathan!Castiel attacks Dean and Bobby with manic delight, remarking: "Oh this is going to be so much fun."
After having revealed themselves to Dean and Bobby, the leviathans quickly realize they cannot remain inside Castiel's vessel as it begins to rapidly burn up and are forced to leave for the time being; they promise to return and finish what they started. Leviathan!Castiel staggers out into the open and submerge themselves in a nearby municipal water source, abandoning the vessel, leaving only Castiel's bloody trenchcoat behind.
The leviathans then disperse to take separate vessels of their own by various means of exposure to the tainted water. One takes a girl whilst she drank from a public water fountain, for example. Two of the creatures infect a pair of gym students and use them to kill and devour two other students, leading Dean to their whereabouts. The creature possessing the girl meets with another leviathan - Edgar - to discuss their next move and the "boss" they take their orders from.
The girl comes up with a plan to solve their feeding problem and steals the form of a doctor - Dr. Gaines - at Sioux Falls Hospital. It then uses the position to acquire easy meals. Its act of cannibalism is witnessed by Sheriff Jody Mills, who escapes the hospital with Bobby's help. Edgar arrives with the two gym student leviathans, which take on the forms of members of staff. Bobby investigates one of the bodies and is confronted by the leviathan Dr. Gaines, who recognizes him from before, when it was inside Castiel.
Bobby subsequently escapes the confrontation and races back home, informing the boys of his discoveries along the way. When they return to his house they discover it burned down and Bobby missing, however. Sam and Dean are then attacked by Edgar the leviathan who informs them that they are considered "competent" enough that the head leviathan wants them dead. The boys succeed in defeating it by dropping a car on it. Both suffer severe injuries, however, forcing Dean to call for an ambulance.
Back at Bobby's, the black blood of the leviathan Edgar, spills back into the body and its hand twitches as a sign of life.
Bobby arrives at the hospital where Dr. Gaines works to rescue Sam and Dean. He tells Dean to meet him in the ambulance bay and tosses him a pair of crutches, then grabs the gurney holding an unconscious Sam. He stows Sam in the back of the ambulance and climbs in the driver's seat. Dr. Gaines receives a call telling him the Winchesters are in the hospital, and with the leviathan nurse he goes in search of the brothers. They spot the ambulance and run towards it. Dean board the ambulance just in time and all escape.
Three weeks later, Bobby's contacts tell him that the Leviathans at the hospital - Dr. Gaines, the head nurse and an administrator - have disappeared. He says that other hunters are reporting similar attacks and that "they're like shapeshifters only a lot more into eating folk. And nothing can kill 'em."
A leviathan has taken the form of an employee working for a credit card company called Chet, and has set up flags on credit cards with the Winchester brothers' known aliases. One is triggered when Sam uses the pseudonym Lemmy Kilmister in Whitefish Montana. Chet calls Edgar for guidance, and Edgar tells him to get after the brothers. He tracks down the location where the card was used, and finds Sam on the security footage. He calls Edgar again to tell him that he is on their trail, then pours a vat of hot cheese on the bound and gagged store clerk, and eats him.
Chet gets instructions by phone as to the Winchesters' location and says he's about a day and a half drive from Prosperity, Indiana. When he finds Sam and Dean, Dean shoots him, but his body simply pushes the bullet out. As Chet is about to attack, Don Stark enters and paralyzes him with some sort of spell, which he says will disable him for a day or two. He advises the Winchesters to put the creature in a bottomless hole.
Sam and Dean bind Chet with chains, and put him in the back of the Impala.
Chet is chained to a chair in the basement of Bobby's cabin, still weakened by Don Stark's spell. Bobby tries every method in the book to find a means to harm the leviathan, but everything fails, much to Chet's amusement. Whilst preparing electric shock, Bobby brushes against Chet's arm, allowing him to take his form in order to mock him on a personal level. Bobby loses his cool and cuts Chet's head off, which seems to be the solution he was looking for.
Bobby later finds Chet re-attaching his head, however, and wonders how else he might harm the monster when something starts to drip through the ceiling and onto Chet, who screams in agony as the liquid burns through his skin. Bobby rushes upstairs to find his guest, Sheriff Jody Mills, cleaning the floor with borax products. He quickly douses Chet with the stuff and beheads him once again, this time keeping his head in a cardboard box and instructing Jody to take it far away and "drop it in the drink" while he buries the body in cement.
Meanwhile, two more leviathans have taken Sam and Dean's form and are going on a rampage from town to town, killing people en masse. This causes the authorities to place Sam and Dean on the top most wanted list and a manhunt begins, with two FBI agents taking a particular interest. The doppelgängers succeed in luring them into a trap and Sam and Dean are arrested by the police.
The leviathans then infiltrate the police station and try to kill the Winchesters, but are caught by surprise when Dean uses Borax against them and decapitates them as informed by Bobby. With their heads missing, one of the FBI agents, actually a leviathan, informs his "superior" of the situation and is advised to adopt new tactics in hunting the brothers.
Elsewhere, the leviathan superior, Dick Roman, enters his limo and is greeted by the demon Crowley, who proposes an alliance between their two factions. Dick coldly refuses his offer, however, considering Crowley a "hideous mutation" and not worthy of his attention. Crowley leaves, insisting the leviathan keep his offering of infant-flesh muffins.
Sam, Dean, and Bobby follow a suspicious meat truck from a Biggerson's Restaurant to a building run by Dr. Gaines. Their first clue that something is very wrong is the arrival of Edgar, who is meeting with Dr. Gaines. Dr. Gaines has been experimenting on food to create an addictive product that will pacify and fatten humans for ease of leviathan consumption. He is behind the new Turducken Slammer at Biggerson's. However, a small percentage of test subjects have a had a bizarre reaction involving massively enlarged adrenal glands that drive them into a zombie-like, cannibalistic frenzy. Their behavior has led to newspaper reports speculating about the Jersey Devil. Edgar warns Dr. Gaines to burn his failed subjects because their leader, Dick Roman, is coming to check on him.
Dick arrives, and Dr. Gaines shows off his lab, in which test subjects are passively watching surgery on television next to a dead relative. Dick likes what he sees, but reminds Dr. Gaines that his work made the papers. Dick wants to make this a "teachable moment" for his other subordinates. His assistant, Susan, places a bib around Gaines's neck, and he reluctantly eats himself alive.
The leviathans capture Bobby, who has been spying on them, and take him to Dick's office. Dick tells Bobby that he is going to eat him, but he is mildly impressed by humanity's achievements, including the gun. He speculates that Sam and Dean will soon attempt to rescue Bobby, who tries to convince him otherwise. Dick is proved correct when Sam and Dean burst into the facility with spray bottles of borax and start spraying the Leviathans. Dick commands Bobby to remain in his office and leaves to take on the brothers, taking a gun with him. Bobby runs to the desk, finds folders of information on Leviathan plans, and grabs one of Dick's fancy weapons. Susan tries to stop him, but Bobby shoots her in the head, buying enough time to get past her.
Sam and Dean try their borax on Dick, and while he burns, he seems less susceptible to damage. The brothers by enough time to get outside the building and start their van. Bobby runs after them and dives inside just as Dick comes out of the building, shooting. He hits Bobby as the van speeds away.
Dean finds Dick in his car outside the hospital where Bobby is fighting for his life. When Dean yells that Dick Roman is there, passers-by start taking pictures with their phones. Dean challenges him to kill him there, but also points out that - being famous - he can't kill him without bringing attention to the leviathans. Dick laughs, seemingly unconcerned by Dean's threats.
Dean has given Frank the numbers 48495 which Bobby wrote on Sam's hand before he died, and also asked him to research Dick Roman. It is shown that the leviathans have recalled the Turducken Slammer meat, presumably because of the bad side effects of the additive. Having not heard from him for a month, Dean returns to Frank's house to find it deserted. Frank confronts him, and they both have to shed some blood to prove to the other they are not a leviathan.
Frank has moved all his equipment into an RV, after feeling he was being watched after he started investigating Dick Roman. Frank says he has found evidence of the leviathans in positions of influence. He tells Dean he has found nothing on Bobby's numbers, but then he tried combinations with adding a sixth number and realized they are coordinates to a field in Wisconsin, owned by Dick Roman.
Frank and Dean travel to the area and disguise themselves as phone company workers. They discover surveillance covering the area and retreat to Frank's RV to monitor it. They discover Amanda Willer, who works for Richard Roman Enterprises, surveying the site for construction. It is unknown if Amanda is a leviathan.
Before he dies, Chronos - the God of Time, tells Dean and Sam:
"You want to know your future? I know your future. It's covered in thick black ooze. It's everywhere. They're everywhere. Enjoy oblivion."
Frank reports that there is nothing new on Dick Roman but that Fred Savage is a leviathan.
Frank reports to Dean that leviathans have infiltrated the luxury cruise ship industry.
Dean continues to insist Frank research the leviathans and try and find out what Dick Roman is planning. Frank reports to Dean, Dick's funding an archaeological dig, a factory in Saudi Arabia, and a fishery in Jakarta. He thinks they are behind the new Biggerson's restaurant in Butte, Montana. Frank tells Dean Tromso in Norway has "zero leviathan activity."
While investigating cursed objects in Portland Oregon, Dean and Sam discover that leviathan Realtor Joyce Bicklebee and her assistant George, are acquiring properties from local owners, and killing those who refuse to sell. In the confrontation that follows, Sam and Dean decapitate Joyce with help from George who plans to eat her in order to kill her. Afterwards, George reveals that the leviathans are planning on building a research facility, in order to find a cure for cancer. When Sam asks why, George replies: "'Cause we're only here to help."
Bobby's ghost reveals that the leviathans are planning on making slaughter houses so they can feast on humans regularly and cure them of cancer to improve their food source. They are also using Turducken style meat to dumb down humanity so that no one will notice and have bought a list of restaurants "ten pages long" to spread the additive. Dick, who has Frank's hard drive, asks his employee, Charlie Bradbury, to hack into it and give him any info that's on it, namely about himself and the Winchesters. He also has one of his minions eat Pete and another pick up a package from an airport containing the Word of God tablet regarding the leviathans. However, Sam and Dean steal it after learning of it from Dick's emails and Charlie helps them by erasing everything on the hard drive. Dick tries to stop them and is attacked by Bobby, who is having trouble controlling his anger towards Dick. Enraged, Dick eats Victor for failing him.
Dick Roman discovers the identity of the prophet Kevin Tran, who has the power to read the Word of God stolen from them by Sam and Dean previously. He orders Edgar to capture the prophet, which he does by posing as a detective and questioning Kevin's mother. As chance would have it, two angels deliver Kevin to his mother and directly into Edgar's hands. Edgar easily kills the angels and takes Kevin. The leviathans also recapture the leviathan tablet which Kevin has with him.
After Kevin is taken away by the angels, Sam and Dean learn a way to kill leviathans from Kevin's translation of the tablet: the bone of a righteous mortal washed in the three bloods of the fallen. They start their search for the needed ingredients by getting fallen angel blood from the resurrected Castiel.
Kevin Tran is captured and taken to the new leviathan headquarters, SucroCorp, where he is forced to translate the Word of God after the leviathans threaten his mother's life. After reading the translation, Dick Roman sends Edgar to kill the Alpha Vampire and get his blood.
Putting their additive in the high-fructose corn syrup SucroCorp makes, the leviathans are able to quickly spread the additive and humanity starts to become mindless just as the Leviathans planned. Dick also does a series of interviews promoting himself and his plans with SucroCorp.
Edgar travels to the Alpha's hideaway and meets with him, sensing that he has Sam and Dean Winchester. The two discuss the leviathan and vampire relationship and the Alpha's worry about the death of other vampires, especially after Sam and Dean told him that the leviathans are purposefully making the food poisonous to them. Edgar eventually admits to this and attacks the Alpha who is no match for him. However, Sam and Dean break free and Sam decapitates Edgar. Edgar's visit has the opposite intended effect: now knowing that the leviathans have betrayed him and owing Sam and Dean his life, the Alpha gives them the blood they need without a fight.
In order to stop Crowley from giving the Winchesters his blood, Dick Roman summons him into a devil's trap at SucroCorp and offers him a deal: Canada in exchange for the demons leaving the U.S. alone and giving the Winchesters the wrong blood. Crowley agrees and the two formalize a deal with a very long contract. However, not trusting Crowley, Dick has the arm of the real Dick Roman brought out and used to have a bunch of leviathans take on his form to confuse the Winchesters and make it so they can't tell which one is him if they come after him.
Dick holds a meeting with a bunch of leviathan delegates working on various parts of the leviathan grand plan. He describes how America will be cut up into different zones each with a different purpose for their plan. He shows them how a modified dairy creamer will hold a modified version of the additive which will weed out unfavorable traits such as thinness. He demonstrates this by having a scientist inject a thin girl named Polly with the creamer which kills her. At the same time, Kevin Tran escapes, but after learning the new plan, is recaptured by Susan.
Sam and Dean, after getting the needed ingredients for the weapon with Crowley betraying Dick like feared, try to locate Dick by hacking into SucroCorp's security cameras using what Charlie Bradbury taught them, but find all of the decoys that Dick set up and are confused. Bobby Singer shows up possessing a motel maid named Louise to try to kill Dick with a machete, but is stopped by Sam and he and Dean then leave to come up with another course of action.
After learning that Castiel, because he was the leviathans' original vessel, can tell the leviathans apart no matter what form they are in, Sam and Dean convince him to help them and launch an assault on SucroCorp. The rogue demon Meg crashes the Impala through SucroCorp's front gate and giant glass sign, allowing Sam, Dean and Castiel to sneak in while they are distracted. Meg decapitates the guards and Sam finds and rescues Kevin and the two plan to blow up the leviathan lab and the poisoned creamer. After finding at least one fake Dick Roman, Dean and Castiel locate the real one in the lab and decapitate the leviathan scientist before confronting Dick. In the fight that follows, Dean, with the help of Castiel, kills Dick, but the two are dragged to Purgatory with his soul.
After the death of their leader, the leviathans are left confused and disorganized which, according to Crowley, is because Dick is the only leader they ever had since creation. With Dick dead, the leviathans are little more than ordinary monsters, tough to kill but manageable. Crowley informs Sam that they have to keep them from getting a new leader and that he has an army of demons outside SucroCorp ready to dispatch all the remaining leviathans inside.
After escaping from Purgatory and reuniting with Sam, Dean proves to him that he is not a leviathan among the other tests he performs (demon, shapeshifter) and does the same to Sam. Later, after finding Kevin Tran, Kevin shoots them with a squirt gun which Dean appears to assume is filled with borax as he informs him as well that they are not leviathans. All the leviathan influence appears to be gone by this time one year later as people are no longer dumbed-down as they were before the assault on SucroCorp and Sam and Dean eat regular food without apparent worry or mention of the food additive.
Castiel reveals that he abandoned Dean in Purgatory as he feared that the more powerful monsters there, including the leviathans that are still in Purgatory, would come after him and he didn't think Dean was safe. However, Dean doesn't care that the leviathans may be after Castiel and convinces Castiel to work with him and Benny to get out.
In a flashback to his time in Purgatory, while arguing with Dean and Benny, Castiel senses Leviathans nearby and the three run, but are attacked by two leviathans. Dean decapitates one, but the other gets the drop on Castiel and nearly kills him before Benny decapitates it.
In a flashback, as Dean and Castiel head for the portal out of Purgatory, two leviathans attack them. They initially get the upper hand, knocking Dean down and beating Castiel up, but Dean decapitates one from behind and Castiel holds the other one in place while he decapitates that one.
In the present, Castiel describes the last thing he remembers in Purgatory as being on the run from leviathans before appearing in Illinois.
Victor Rogers mentions the past leviathan situation as a "fiasco" and a "wake up call."
While trying to figure out what is killing people and turning their insides to "jelly," a leviathan is suggested, but the idea is discarded. Eventually its figured out that what they are dealing with is a "bastard off-shoot" of a djinn.
Leviathans in Lore
In the Judeo-Christian tradition a leviathan is a giant sea monster, described in the Book of Job. The Talmud Baba Batra 75b states that the archangels Michael and Gabriel will be the ones who slay the Leviathan. Other legends say God will slay the beast. (Source: Leviathan in Judaism)
Death also refers to the leviathans as "the Old Ones" a term used by H.P. Lovecraft in the Cthulhu mythos to describe ancient powerful alien beings who come to Earth. A race called the Old Ones also features in Stephen King's Dark Tower series. In Binsfeld's Classification of Demons, Leviathan is the name of Envy, one of the Seven Deadly Sins.
- Sera Gamble and Bob Singer talk about Leviathans with AOLTV