The Darkness

The Darkness is a primordial entity which has existed throughout eternity. After God came into being, He created the Archangels to fight a terrible war against it. Not even the combined power of God and the archangels could destroy it, so God succeeded only in sealing it away using the Mark of Cain as a lock and key. Whilst the Archangels battled it, this force is so ancient and mysterious that the Demons and even the Angels didn't believe it existed. Both Heaven and Hell thought it to be a "myth" or "scary bedtime story", told to keep others in line.

When Rowena used a spell from the Book of the Damned in order to free Dean Winchester of the Mark, the Darkness was unleashed once again. While on earth, it has taken the form of a woman, and spread a disease of darkness through human beings. She is somehow bonded, or one with the baby Amara.

History
According to Death, before there was the Earth, before there was any light or even God Himself, there was only the Darkness. This being is credited as a powerful, amoral, horrible, destructive force that nearly obliterated anything in its path, causing nothing but chaos. Some time after, God and Death came into being. God created the Leviathans, possibly to help fight the Darkness, as Death claimed long before God created Angels and Man, He made the first beasts, known as Leviathans. As they were too destructive, He banished them to Purgatory. He then created Archangels, beings of supreme light, after he locked away the Leviathans. God and His newly created Archangels battled with The Darkness in a terrible war. Whilst even together they couldn't defeat the Darkness, God eventually sealed it with a mark that would later be called the Mark of Cain. He then gave the mark to Lucifer, his favorite angel and most valued Lieutenant, to guard. The Mark however showed itself to be a curse; the dark effects of which corrupted Lucifer, leading to a chain of events that would see Lucifer cast out of Heaven. Lucifer then transferred the mark on to Cain who then, thousands of years later, passed it on to Dean Winchester.

Season 10
The Darkness was eventually freed with the destruction of the Mark of Cain, as Dean was the only living host of the mark remaining, where it rained down destruction and made a move to consume everything in its path.

Season 11
"We’re bound, Dean. We’ll always be bound. You helped me, I helped you. No matter where I am, who I am, we will always help each other."

- Amara

Shortly after breaking out of her prison, she spared Sam and Dean's life and thanked Dean for freeing her. She mentioned that she already helped him and Dean helped her, bound for eternity, she said they will always help each other. Michael or Lucifer recognized her release and one of them tried to warn the outside world. She temporarily assumed the form of an adult female human, but has since became one with a human baby, going by the name of Amara. Following the Darkness' release, Sam began searching for a cure for the people infected by her. His search led him to find that Holy Fire cures her victims, but as Amara the Darkness began displaying telekinesis, causing Jenna to call Dean back. Her grandmother called an exorcist who was actually Crowley and Dean finds the Mark of Cain on Amara's chest, causing him to realize she is the Darkness. Amara had consumed Jenna's soul and shortly afterwards grew into a little girl. Amara left and later encountered Crowley who offered her people to feed off of.

Powers & Abilities

 * Immortality - The Darkness predates everything, including both God and even Death itself. It even claimed that it didn't know who Death was, and that Death didn't know her. It is an ageless and invulnerable force which cannot die.
 * Nigh-Omnipotence - Castiel describes the darkness' power level as near infinite. It is so unimaginably strong that even God (a being who can do almost anything) couldn't just defeat it, and needed the combined power of Him and His archangels to eventually seal it away. Even Death was willing to make sure the Mark of Cain, the lock on the Darkness, wasn't broken. Considering the force it took just to fight it back and imprison it, the Darkness is the most powerful evil force in the Supernatural universe. She seems to have a distributed consciousness or at least some kind of local Omnipresence, while a part of her talked to Dean, the smoke form part of her was still expanding around them.
 * Nigh-Omniscience - Despite spending billion of years imprisoned, she was immediately able to speak the English language, however she claimed to not know who Death was.
 * Reality Warping - While she talked to Dean her smoke form was still expanding, causing immense winds, however they were completely unaffected by them, indicating that she has tremendous control over the physical universe.
 * Flight - The Darkness, while disembodied, can fly in a similar manner to demons and angels without a vessel.
 * Invulnerability - Considering its ability to stand against God and his archangels, the Darkness can be assumed to have an immense resilience to physical and supernatural attacks that likely constitutes invincibility.
 * Weather Manipulation - As The Darkness expanded on earth it caused strong winds.
 * Apporting - She was able to teleport Dean out of his car without merely a word.
 * Telekinesis - In the form of Amara, the Darkness displayed telekinesis.
 * Soul Consummation - In the form of Amara, the Darkness was able to eat Deputy Jenna Nickerson's soul which made her to grow into a little girl.
 * Corrupting Affect - The Darkness seems to be a corrupting force to whatever it comes into contact with. It corrupted the Mark of Cain to a curse that would make killing the host impossible, even for Death an entity that was immensely strong in his own right. It also corrupted anyone with the mark into a killer. When released, those who came in contact with the initial release of the Darkness turned into a meaningless killer. Billie told Sam that he was unclean in the biblical sense from being infected by a rabid.

Weaknesses
The Darkness is beyond destruction as it is amortal, not technically even alive; however it has weaknesses, and is possible to seal away.
 * High-Tier Entities - The combined strength of God and the archangels was strong enough to bind the Darkness, and seal it with a lock.
 * The Mark of Cain - The Mark of Cain was the "lock" to the prison that held the Darkness back. As long as one person bore the Mark, the Darkness would remain sealed. With its removal, the Darkness was set free once more.

Appearances

 * Season 10
 * Brother's Keeper


 * Season 11
 * Out of the Darkness, Into the Fire
 * Form and Void
 * The Bad Seed

Trivia

 * The Darkness is similar to many terms and entities found in many creation myths.
 * Chaos/Nun in Greek/Egyptian mythology, which predated everything and created or from which the gods came from.
 * Ginnungagap from the Norse Creation Myth. Was a primordial void.
 * The terrible battle between God and the Darkness seems to fit with the first day of creation in Genesis. "Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters. And God said, “Let there be light,” and there was light. God saw that the light was good, and he separated the light from the darkness." It is possible that the "light" he created was the archangels, and him he separating the "light" and "dark" was Him locking away the Darkness.
 * The name Amara occurs in many cultures and is ascribed a variety of meanings: "eternal" (German), "unfading" (Greek), "immortal" (Sanskrit) and "bitter" (Latin). In Bahasa Indonesia the word amara(h) means "anger" or "run amok". In Ethiopian legends, Amara is the name for paradise.
 * Name Amara is similar to name Samara from movie "Ring".
 * It is the true source of where Knights of Hell come from, channeled though The Mark of Cain.
 * It is likely that The Darkness is the progenitor of all evil that has ever existed in the Supernatural universe.
 * The Darkness is the fourth entity either that was sealed away to be unleashed, the first being a huge number a demons, the second being Lucifer himself, and the third being the Leviathans.
 * The Darkness predates the Universe.
 * Releasing The Darkness is overall easier than freeing Lucifer, but the spell to release the Mark was not even known of until recently, previously making removing the Mark impossible. In contrast, it was known Lucifer could be freed, but was very hard to do, where the Darkness was believed to be eternally bound, but once the spell was revealed, was rather easy to release.