Astaroth

Astaroth was a demon who worked to condemn humans' souls to Hell by turning them into witches. In "Malleus Maleficarum", she turned Renee Van Allen, Elizabeth, and Amanda Burns into witches, which resulted in several deaths, including the entire coven in question. The Winchesters' investigation led them to Astaroth and they ended up killing her.

Background
Astaroth was hundreds of years old. In the fourteenth century, she came into contact with a human whom she taught witchcraft to in exchange for the human's soul, which went to Hell and became another demon, named Ruby.

Astaroth herself later ended up in Hell. She managed to escape when a Devil's Gate was opened in "All Hell Breaks Loose - Part 2"; when talking about the escape later with Ruby, Astaroth described escaping Hell as "a bitch of a fight" and was impressed that her student had made it.

Astaroth was a devout follower of Lilith. In attempt to please Lilith, Astaroth and her "friends" sought to hunt down and kill Sam Winchester to eliminate Lilith's "competition" for leadership of Hell.

"Malleus Maleficarum"
Astaroth secretly possessed Tammi Fenton in order to "break the ice" with Tammi's friends Amanda Burns, Elizabeth, and Renee Van Allen. She then brought the Book of Shadows into the women's book club, and tricked them into unwittingly selling her their souls in exchange for her improving their lives.

Amanda used witchcraft to kill her lover Paul's wife and then tried to kill Paul himself, bringing Sam and Dean Winchester to investigate. Astaroth planted a hex-bag that killed Amanda in a way that appeared to be a suicide, and later cast a spell to kill Dean, although Ruby intervened to break the spell and save Dean.

When Sam deduced that Tammi was possessed, Astaroth briefly kept up her charade before dropping it and taunting him by claiming that his brother was already dead. Sam tried to shoot her with The Colt, but she telekinetically slowed and then stopped the bullet completely, making it fall to the floor without hitting her. She incapacitated him, killed an angry Renee out of annoyance, and taunted a horrified Elizabeth about having sold her soul without realizing it.

Astaroth started trying to kill Sam by crushing him to death. When Dean and Ruby arrived, Astaroth incapacitated Dean as well, but allowed Ruby to explain why she was there; Ruby claimed to have lured the Winchesters to Astaroth as a gift and that she wanted to serve Astaroth again. Astaroth appeared to consider Ruby's words for a moment, but then Ruby tried to kill her, leading Astaroth to brutally beat Ruby. She began to exorcise the younger demon, only to be caught off-guard by Elizabeth's spell, causing her to release Sam and Dean and kill Elizabeth. Her brief distraction allowed Dean to retrieve the Demon-killing knife, grab her from behind and stab her several times, killing her.

Powers and abilities
Astaroth was an extremely old and powerful black-eyed demon. She overpowered Sam, Dean, and Ruby with ease when they attacked her; however, when she was distracted by a spell Elizabeth performed, Dean managed to kill Astaroth when catching her by surprise.


 * Possession - Astaroth secretly inhabited Tammi's body in order to trick Tammi's friends into becoming witches.
 * Spell-casting - Astaroth had extraordinary knowledge of witchcraft, which she taught to her pupils in exchange for their souls. Astaroth was not reliant on hexbags, and she could cast similar spells without ever needing to plant one. She also knew an exorcism which would send other demons back to Hell without affecting her, which she started to use on Ruby. She was also the one who taught Ruby all she knew about magic.
 * Super strength - Astaroth was much stronger than humans as well as fellow black-eyed demons, as shown when she easily overpowered Ruby during their fight (although Ruby was a weak demon).
 * Invulnerability - Astaroth could not be killed by old age, disease, or injuries dealt out by ordinary weapons. She also had some degree of immunity to iron, as she held a fireplace poker without any visible pain and used it to beat Ruby. However, she was killed when stabbed repeatedly using the Demon-killing knife, and was vulnerable to The Colt.
 * Immortality - As a demon, Astaroth could potentially live forever, she was over seven hundred when she was killed.
 * Telekinesis - Astaroth broke Renee's neck with a wave of her hand. She also pinned Sam and Dean to walls and held them incapacitated without effort while she concentrated on fighting Ruby, even beginning to psychically crush Sam to death at one point; however, she lost control of them when attacked by a spell that made her cough up pins. She also stopped a bullet from The Colt in mid-air, a feat no other demon has been shown capable of (although the majority of demons are often caught by surprise).
 * Reality Warping -  Astaroth granted the wishes of the coven once they sold her their souls; this included getting Elizabeth's husband a promotion as well as having her win a trip to Hawaii, and improving business for Renee's pottery business.
 * Biokinesis - Astaroth killed Elizabeth by telekinetically stopping her heart.

Trivia

 * Although she was not named in the episode, Astaroth's name was revealed in the Supernatural Companion for Season 3.
 * Astaroth was the second demon of lore to appear in the show; the first was Azazel.
 * In lore, Astaroth is the demon of laziness, vanity and rationalization. It is also said that he grants power to magicians who summon and kneel before him.