Leviathans

''"They're pretty much like shapeshifters, really, but more into eatin' folk and nothin' can kill 'em." - Bobby Singer''

Leviathans, also called the Old Ones, were God's very first beasts, and thus pre-date angels, humans, and the soul itself. Being too much of a nuisance, God created Purgatory and locked them in there.

Characteristics
''"Long before God created Angel and Man, he made the first beasts: The Leviathans." - Death''

According to Death, the Leviathans were among God's earliest, if not his first, creations. Unfortunately the beasts proved to be too powerful and destructive and God was concerned they would destroy everything around them so he sealed them away in Purgatory. Death describes them as "clever and poisonous".

In spite of their chaotic nature, it is established that the Leviathans have a strict hierarchy, with several of them taking orders from their leader, Dick Roman. Under Roman's command there are head Leviathans who in turn have authority over other Leviathans. It is Roman's orders that send several Leviathans to hunt down those in their group who have been feeding indiscriminately and to deal with the Winchesters and their allies. It seems that the higher-ranking Leviathans have an easier time controlling their hunger.

Their true form hasn't been shown, but they seem to take on a serpent-like shape while under water. A leviathan doesn't necessarily need a vessel to function, because they functioned quite well when there wasn't anything to possess, but it does help. Once a vessel is taken, the Leviathan is able to shapeshift without taking a new one. When in a host, they can dislocate the jaw and reveal a mouth full of large teeth and a twin-forked tongue.

Powers and Abilities

 * Invulnerability: There is no known way for a hunter to kill a Leviathan, and they heal quickly from physical injuries. The only way to cripple one is to remove its head and hide it so that it can't reattach to its body. Borax is extremely caustic to Leviathans, but not deadly.
 * Regeneration: Leviathans can heal wounds they receive and can even reattach their heads when cut off.
 * Possession: Leviathans are able to take over a human body, much like demons can.
 * Shapeshifting: Leviathans are to shapeshift to match anyone whose DNA they have access to. This also allows them to access their form's memories. Unlike the later shapeshifters, they have the ability to mimick a human's specific clothing as well, making it even easier to impersonate people.
 * Super strength: Leviathans are uncontrollably strong, being even able to overwhelm angels, and are stronger than demons.
 * Immortality: The Leviathans is immortal, through having an ageless lifespan, meaning that they does not age at all. A Leviathan is immune to death by natural causes and aging.

Vulnerabilities

 * Hunger: Leviathans are constantly hungry, which can lead them to making mistakes, such as becoming distracted or revealing their true form. Leviathans are also a cannibalistic species; the only known way (currently) to destroy a Leviathan is for one to eat another, or for one to eat itself.
 * Witchcraft: It's unknown if witchcraft can kill a Leviathan, but it can stun and weaken it for an extended period.
 * Decapitation: By removing a Leviathan's head, the Leviathan is rendered unable to act. However, the head must also be hidden to keep it from reattaching.
 * Borax - Borax is extremely caustic to Leviathans, weakening them and eating their flesh much like Holy Water does to demons.
 * Unused methods(Methods that havent been used to kill a levithan or harm them)-ripping them in half, too much physical damage to the body to heal from, ripping them apart layer by layer(skin, flesh, blood, organs, bones), total physical destruction of head and body(ex-fire, freezing, etc.), the colt, any other unknown method or creature that can harm/kill a levithan

Season 7
When Castiel cracked open Purgatory and imbibed the souls found in there, he also unknowingly absorbed the Leviathans. After some time, they began manifesting in him and asked him to let them out.



Due to their uncontainable power, Castiel's vessel began deteriorating, until he could no longer hold it together. Coming to Sam and Dean for help, he, with the help of Dean and Bobby, opened the door to Purgatory again and hurled the souls back in. Shortly after Castiel had got rid of the souls and his body was repaired, he realized the Leviathans were still inside him. Unable to hold up against them, he finally succumbed and the Leviathans surfaced, telling Dean that Castiel was now "gone". Relishing their new-found freedom, they inform Dean that now they are going to have fun.



However, they are soon forced to leave Castiel's body due to the vessel being unable to handle them. So using Castiel, they head to a water reservoir and, using the water, spread to the population, taking new vessels, thus possessing multiple people. They then break into two distinct groups of those who can control their hunger and proceed to observe the human world and those who act careless in their feeding; drawing attention.

Two Leviathans meet in a park to discuss the current situation. The Leviathan possessing Edgar reveals to the Leviathan in the girl's body that he is here because the "Boss" heard about the careless feeding of some of the others and is angry that it has drawn human attention. He tells her to get the Leviathans in the area in line because their leader "hates bad news".

They realize they can't leave Sam, Dean and Bobby alone, and decide to get rid of them. This leads to them burning Bobby's house and the Leviathan possessing Edgar attacks Sam and Dean. Sam and Dean managed to get away, and Leviathan set their feelers out. They begin tracking the Winchesters, flagging their credit cards. Chet manages to catch up with Sam and Dean, but is stunned by Don Stark. Sam and Dean put the body in the Impala.

Later two Leviathans impersonate Sam and Dean and go on a bloody rampage; turning the brothers into public enemies and to draw them out of hiding. Thanks to Bobby discovering the Leviathans weakness to Borax they are able to deal with their dopplegangers and again convince the world they are dead. The leviathans disguised as FBI agents come to collec the bodies, but the sherif lies to them. The Leviathan returns later and kills the Sherif and his daughter.

Elsewhere Crowley meets with the leader of the Leviathans who is impersonating buisnessman Dick Roman. Crowley attempts to secure an alliance with the Leviathans but Roman see's through Crowley and tells him he would rather "swim through hot garbage than shake hands with a bottom feeding mutation like you." The creature explains that it sees demons as lesser than humans, whose only use is a food supply. Roman tells Crowley not to bother him again and warns him that, if not currently occupied with other matters, the Leviathans would wipe demonkind out in a heartbeat.

While the brothers work to discover the Leviathan's master plan they learn from the deity Chronus that the Levianths will soon cover the earth leading to oblivion.

Known Leviathans

 * Castiel (He initially hosted all the Leviathans, up until they disposed of him, taking on all new forms)
 * Dr. Gaines/Annie
 * Edgar
 * Chet
 * Agent Valente
 * Agent Morris
 * Dick Roman
 * Susan

Trivia

 * They are the main antagonists of Season 7.
 * They are possibly based upon the biblical sea monster mentioned in Job 41 or the biblical sea monster mention in the first chapter of Genesis as the first inhabitants of the seas.
 * The Leviathans are unusual in the Supernatural universe in that they are the only creatures to possess another creature which is using a vessel, because they possess Castiel while in the possession of Jimmy Novak. Similarly, Azazel was able to possess a reaper while it assumed human form.
 * They were referred to as "The Old Ones" by Death. This may be a reference to the ancient creatures described by H.P. Lovecraft, who had previously created a portal to Purgatory, where the Leviathans were once imprisoned.