Soul

Souls are the spiritual life essence of a human or monster, which resides within a physical body while they are still alive. After their physical body dies, or is destroyed, their soul continues to exist, and typically moves on to an afterlife. After death, humans can refuse to move to an afterlife, and remain on Earth as a ghost. If they go to Hell, they will end up being tortured into a demon. Monster Souls go to Purgatory. And when a demon gets killed, the soul goes to The Empty.

Creation
"You throw your life away because you've come to assume that it'll bounce right back into your lap. But the Soul is not a rubber ball. It's vulnerable, impermanent, but stronger than you know. And more valuable than you can imagine."

- Death

When God created humans, he gave them a spiritual essence or soul, so that after their physical bodies perished, they could move on to either be rewarded or punished, depending on the life they chose to lead. Eve, the Mother of All, created monsters whose souls function similarly, but are destined instead to Purgatory.

In the Natural Order, human souls are transported to the afterlife by Death's servants, Reapers; however, the reaper Tessa refused to tell Dean on more than one occasion where she takes them. Known destinations of souls are Heaven, Hell, The Empty and Purgatory. However, when Metatron closed Heaven the human souls were stuck in the Veil, waiting for its reopening. Souls have since been shown being able to move out of the Veil once more, how this was accomplished is uncertain.

According to God, creating souls had made him feel "nauseous".

Characteristics
"What do you think the soul is? Some pie you can slice? The soul can be bludgeoned, tortured, but never broken. Not even by me."

- Death

Souls are magical by nature and could be used by several creatures to cast spells or to increase their power. They are said to be impermanent and immune to harm. Death claimed that not even a being as powerful as him could break a soul apart, however it is shown that the inner key to oz is able to accomplish this feat, showing that it can, in fact, be done to some degree. It should be noted that while separated, they still shared a link that whatever physically happens to one happens to the other one. A soul can't be fully destroyed, because even if a demon is killed, the corrupted human soul is cast out into The Empty.

It was previously thought that burning their bones would get rid of them completely, but that was shown to be untrue. Missouri Moseley claimed that Mary Winchester's spirit was completely destroyed, but seeing as multiple people were confident they could bring her back to life, this is still unknown. According to Henry Winchester, a damaged soul could heal in due time. Usually, souls leave their vessels when they die, being taken to their final place, but they can be removed by force, leaving their owners soulless. However, it seems souls have a link to their vessels; when removed, the souls return to them (if they are still alive) when they have the chance to do it.

A large number of souls could be used to build a Soul Bomb supposedly capable of killing the Darkness. It is known that one soul contains the same amount of power as one-hundred suns.

According to Castiel, the human soul would theoretically act as a filter for the prophet translating the word of god and inoculating them from any of the corrupting effects of the tablet's power. Since Donatello did not have his soul anymore, he was corrupted by whatever darkness contained within the Demon Tablet.

Deals
In exchange for a soul, Crossroad Demon's will grant humans any desire they wish. Once the exchange was completed, the demon usually would give the person ten years before they came to collect. It can be as little as one year (Dean's deal) to as long as twenty-five years (Becky's possible deal). Either way the demon has to collect and send the soul to Hell, other higher demons like Astaroth, the Princes of Hell, White-eyed Demons and even angels as seen with Balthazar can make deals and hold contracts as well.

Gaining Power
Beings can use souls to gain more power. Castiel used Bobby Singer's soul to heal himself; he also used the power of 50,000 souls to blast Raphael, effectively starting the civil war in Heaven. Angels are also able to absorb and transfer memories from souls. When Castiel opened a portal to Purgatory using a ritual, he absorbed the millions of souls of every monster there and the power he gained from them was enough to trap and kill Raphael with ease. The souls from Purgatory also made Castiel immune to the deadly effects of an Angel Blade. With his own power drastically augmented, Castiel claimed the title of God. It is also shown that Eve can draw power from the souls in Purgatory, calling it "her supply". After the Grigori Angels turned away from Heaven, and were almost completely destroyed, some of them began to slowly feed on human souls, gaining power. This slowly damaged their soul, which could not be healed by other Angels. However, after the victim is dead, should their soul go to Heaven (if any of their soul remains intact), they appear to return to normal, fully healed. Monsters such as Crocotta suck the soul out of their victim, consuming it and gaining its power. It is stated in Alpha and Omega that a single soul has about as much power as 100 Suns and hundreds of thousands of souls are thought to be enough to destroy the Darkness, an entity more powerful than God himself. In The Foundry, the ghost Hugo Moriarty was able to bind the souls of the children he murdered to himself and draw on them to gain an incredible amount of power. The children were unable to pass on even after their bones were salted and burned until Hugo himself was destroyed.

It is shown that a large amount of souls can cause damage to vessels, as seen when Castiel absorbed the 30-40 million souls of Purgatory, his vessel started to melt as a result of holding all those souls, and would've exploded, potentially taking a chunk of the earth with him, had he not returned the souls to Purgatory.

Spells
To perform certain spells, one must tap energy from their soul. It will eventually heal, and retain full power, so that the spell caster may preform the spell again. An example is the time traveling spell. This spell was introduced in As Time Goes By, when Henry Winchester traveled to the twenty-first century through a closet. The body can be made uninhabitable for a soul by use of a spell, that requires the person to commit patricide. According to Balthazar who suggested this to Sam, ''"You need the blood of your father, but your father needn't be blood." ''One could kill not just their father but also a father figure for the vessel to become scarred.

Splitting
It has been shown that you can split a soul into two, making them separate, yet identical, beings. To accomplish this, you need extremely powerful magic. An example of this is the Inner Key to Oz. This key can unlock a persons soul, allowing you to split it into separate persons, generally separating the good from the bad. Although the souls are now separate, their bodies are still connected, so if one of them is damaged, so is the other. This split can be reversed by using the key again. (It should be noted that the split soul parts are still connected, leading to believe Death meant that a soul cannot be split completely, leaving no connection between them).

Weapons
Due to the sheer power of souls, they can be used as weapons on occasion. Castiel weaponized the souls of Purgatory in order to win his war against Raphael before proclaiming himself to be the new God. When faced with the daunting task of killing the Darkness, a being God suggested could potentially be killed with the light of 10,000 suns going supernova at once, Castiel suggested using souls to power such a blast. With the help of the Reaper Billie, the Winchesters and Rowena were able to create a Soul Bomb made out of a couple of hundred thousand souls presumably capable of killing the Darkness, the oldest being in existence. In the non-canon novel Supernatural: Bone Key, the demon Fedra was able to use a ritual to imbue Dean with all the ghosts of Key West and their spiritual energy. By channeling different emotions, Dean was able to weaponize the power he got from the souls within him in various ways. The souls were also able to communicate with and guide him in using that power.

Humans
Human souls are the spiritual essence of a person, which typically reside inside a physical body. After that person dies, should they choose to move on, a reaper will take them to either Heaven or Hell, depending on how they lead their life. The soul allows the body to feel emotions, such as happiness, sadness, and remorse, and for an unknown reason, it makes it so that humans need to sleep. Human souls hold an immense amount of power, said to contain the power of at least 100 stars.

Demons
Demons are human souls which have been twisted and tortured until they are nothing but a cloud of black smoke. This occurs when a human soul goes to Hell, either by making a deal, witchcraft, or leading a bad life. They will be tortured by other demons, until they become one themselves. To manifest on Earth, most demons have to possess the bodies of humans and use them as vessels except for Acheri and Daeva. As their soul is twisted, their emotions become corrupt, where they no longer feel sympathy or empathy. They also gain powers, which they can use in Hell, or while possessing a vessel on Earth. Using the Demon Curing Ritual, a demon's soul can be returned to its original human state.

Ghosts
Ghosts are human souls that refuse to move on to an afterlife, and remain on Earth. They typically reside in The Veil, but with enough strength they can manifest in the physical plane, usually in the form of their past bodies. Staying on Earth usually turns souls into violent spirits, however. Like demons, they are also able to possess humans to accomplish things. When they are put to rest, a Reaper takes them to where they belong.

Angels
It was revealed in Sacrifice that when an angel loses its grace, they become human-like (having no powers or immortality). This allows them to feel more human emotions, as angels typically don't feel them. When an angel has no grace, and is reduced to a soul-like spirit, it can move on to an afterlife, such as Heaven or Hell, after it dies.

Monsters
Monsters are humans that have been tampered with, and altered by Eve. It has been shown that not only are their bodies physically different than humans, but their souls are altered as well. When a monster dies, its soul goes to neither Heaven nor Hell, but instead goes to Purgatory.

Nephilim
Nephilim have a special kind of soul which is essentially the same as a humans but is mixed with angelic grace. This mixture of soul and grace makes it extraordinarily powerful.