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. This force is so ancient and mysterious that even the Angels didn't believe it existed, rather they thought it to be a "scary bedtime story".

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.

History
According to Death, before there was any light or God, there was only the Darkness. This being is credited as a powerful, amoral, 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 to 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. He eventually sealed it with a mark that would later be called the Mark of Cain. He then gave the mark to Lucifer, his 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 passed on the mark to Cain who then, thousands of years later, passed it on to Dean Winchester.

Present Day
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. It presumably will assume the form of a female human, going by the name of Amara.

Powers & Abilities

 * Immortality - The Darkness predates everything, including both God and even Death itself. It is an ageless and invulnerable force which cannot die.
 * Nigh-Omnipotence - It is so unimaginably strong that even God (a being who supposedly can do absolutely anything) couldn't just instantly defeat it, and it took 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.
 * 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.

Weaknesses

 * 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

Trivia

 * The Darkness is similar to many terms and entities found in many creation myths.
 * Chaos in Greek/Egyptian mythology, which predated everything and created or from the gods from.
 * The terrible battle between God and and the Darkness seems to fit with the first day of creation in Genisis. "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 seperating the "light" and "dark" was Him locking away the Darkness.
 * It may be the true source of where demons come from, based on the fact that Lucifer created the first demons after becoming corrupted by the Mark and that every human that has had the Mark was at some point transformed into a demon. IF this is true it could theoretically corrupt any spirit to become like a demon. A demon's essence, although much smaller, even looks almost identical to the Darkness' true form upon its release.
 * It may even be why the Leviathans became so hungry, dark, and destructive, wanting to consume all in their path, as it may have corrupted their essence before God banished both the Darkness and the Leviathans away to other dimensions.
 * Despite being older than God himself, the Darkness will manifest in human form on Earth. Whether or not it chooses to take this form is unknown. The Darkness also was called a (she) so it is insinuated that the Darkness will take a female shape and form.
 * It is likely that The Darkness is the progenitor of all evil that has ever existed in the Supernatural universe.