Leviathan (Supernatural)

"Why do you think he created Purgatory in the first place? To keep those clever poisonous things out."

- Death explaining the Leviathan

Leviathans are the main villains encountered in the seventh season of Supernatural.

Appearance and Anatomy
The true form of a Leviathan has not be seen so far in the show but a glimpse of them under the water shows a serpent-like shape.

To blend in on Earth Leviathans take human vessels. These vessels appear completely normal but bleed a black oily substance when injured

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When a Leviathan is attacking or feeding they dislocate the jaw of the vessel to monstrous proportions to reveal a mouth full of sharp teeth and a twin forked tongue.

Diet
Leviathans have an immense near unquenchable appetite for human flesh. It is implied they need to eat daily to survive and function properly on daily basis, more experience and elder Leviathans can control the hunger while younger Leviathans act rash in their killings. Each Leviathan may be different, as one may enjoy a preference on their meal by adding ingredients such as cheese or garlic to their food while some other will rather try to evoke emotional responses in their victims to flavor the meat.

Abilities

 * Aaaa.jpg shifting: After taking a vessel a Leviathan is capable of shapeshifting into another person provided they have a sample of DNA. This can be acquired through physical contact or a strand of hair.
 * Super Strength: Leviathans are stronger than normal humans.
 * Possession: Leviathans can take over human bodies
 * Regeneration: Leviathans have a frighteningly efficient regeneration. Severed limbs and their heads are capable of reattaching themselves after separation.

Weaknesses

 * Borax: It is discovered that Borax is the only known substance capable of harming a Leviathan. Exposure to the chemical burns severely in the same way a human exposed to powerful acid would react.
 * Decapitation: While the head of a Leviathan can reattach, separating the head and taking far enough away from the body appears to be the only way to put a leviathan down.
 * Magic: Certain spell can temporarily paralyze them.

History
In the beginning the Leviathans came into existence as God's first attempt at creating life. Unfortunately the creatures proved too powerful and destructive and God eventually sealed them into Purgatory to protect the world from their power and hunger.

The Leviathans though were unleashed upon Earth, after a Seraphim named Castiel absorbed all the souls within Purgatory to become the new God. In the end Castiel seeing the error of his ways, tried to return all the souls to Purgatory, but the Leviathans latched unto his body, and took over, before escaping out into the world, possessing various humans as hosts.