Azazel is a Yellow-Eyed Demon, and is the only one seen to date. Azazel is a servant of Lucifer. On at least one occasion, Azazel has called Lucifer his "daddy", a reference to Lucifer's role in creating demons. Azazel was King of Hell during Lucifer's imprisonment, although the term was never used to describe him. However, the demon Casey did describe him as a tyrant who held the demons all together. The only weapon described as having the power to kill Azazel is The Colt. Azazel was integral in Lucifer's plans to escape from his his prison. On Lucifer's instructions, he created the Special Children. Azazel is impervious to Holy Water and has yellow eyes (iris and pupil). He possesses human hosts, but can exist in a disembodied form also, and has the ability to possess a reaper. He can create and manipulate fire, is telekinetic, and has pinned humans to the walls and the ground using this power. He has the power to cause internal bleeding and grievous wounds with his mind. He can enter a human's subconscious; he is able to enter Sam's mind and he shows Sam what really happened to his mother. He displays superhuman-strength, has the authority to make deals and is impervious to the salt barrier. His only weaknesses are "The Colt" and iron. Dean ends up killing him with the colt at the end of Season 2.
Death is one of the Four Horsemen of the Apocalypse, referred to in the Book of Revelation as the Pale Horseman, he appears to be the eldest of the four, older than Famine, War and Pestilence. According to him, he is the only being in existence that will persist through the end of time. According to Death neither he nor God can remember which of them is older. Death also believes at the end of time, God himself will die, and he will then reap God. Death created reapers to serve him and his purpose to keep balance of the Natural Order. He is immortal by default. He is indestructible, although it is implied by Crowley that Death's scythe can harm him). He can raise the dead and resurrect anyone he wants and can manipulate the weather to whatever he chooses or wants it to be. He is omniscient - Has extensive knowledge of the universe and is omnipotent - Can practically do whatever he wants and go wherever he wants. He can be bound (as he was imprisoned for thousands of years beneath the Earth). Assuming what Crowley said to be true, Death's scythe can harm him.
A tulpa is the given name to anything formed through the meditation (focusing) of an idea. The theory is that if you meditate hard enough on an idea, it will materialize. Tibetan monks practice this often, and teach it as part of their learning. Tulpa do not have to be live-creatures but can also be inanimate objects, animals, furniture, or creatures. There is a theory that the entire universe was made through tulpa meditation. A tulpa is hard to define, as anything could possibly be a tulpa. While the idea is still being focused on, the object or creature may change & morph into different forms as the idea itself changes. Tulpa can only be destroyed by eliminating the thought (if the tulpa is not yet formed properly), or the diluting the concentration of the though, then destroying the object or creature.
Veritas is the Roman goddess of truth. She made people say the truth so they would kill each other to pay her fee. Veritas is summoned by a young woman named Corey using a cat's skull, grains of paradise seed, and Devil's Shoestring. As a result of her summoning, anyone in her presence in Calumet City, Illinois who asks aloud for the truth invokes her curse. After being summoned to a location, anyone who asks aloud for the truth invokes her curse. When a person is cursed by Veritas, everyone he or she encounters has to speak the truth. Usually these truths are harsh and drive the person to commit suicide. She takes the bodies of her victims as tributes and feasts on them. She has cat-like speed and agility. Dogs are her Achilles' Heel. She can force people to speak the truth to her. Being stabbed with a knife dipped in dog's blood will kill her.
The Whore of Babylon is a creature from Hell whose name also appears in the Book of Revelation. According to Castiel, it cannot leave Hell until Lucifer has broken out of his Cage and is walking the Earth. This creature wanted to harvest and prepare humans souls for Hell. Her primary goal - condemning human souls to Hell by speaking falsely of prophecy - suggests that she is the "False Prophet" described and mentioned in the Book of Revelation. It can assume human form and read human minds. It's a telekinetic being, which allows it to influence and move objects and people with its mind. This creature understands the Enochian language and seems to be semi-fluent in speaking it; she recited a spell that harmed Castiel, and she also influenced a small town and taught them a false Enochian exorcism that when translated by the Castiel means "you breed with the mouth of a goat". This creature can be very manipulative and she, while in human form, almost condemned an entire town to Hell. This creature also has power over the will of demons and uses this to "predict" where battles will occur thus strengthening the belief in her being a prophet. She can only be destroyed by being impaled with a stake or branch of cypress from Babylon by a true servant of heaven.
A witch is a person who has the power to effect change by magical means ("witchcraft"). Most of those encountered by Sam and Dean are practitioners of Black Magic - that is, spells used for self-gain or to harm others. In 3.09 Malleus Maleficarum, it is stated that witches get their power from Demons - presumably in exchange for their souls. It is notable that Sam, Dean, and Bobby often use the same spells and rituals, but would not consider themselves witches. Witches can be extremely long lived. Only two of the witches encountered has been able to be killed by a hunter.
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