Blood

Castiel uses Dean's blood to track down Balthazar.

Blood is an important component in many rituals, weapons, spells, and other aspects of the supernatural world.

Usage

Rituals and spells

An angel Banishing Sigil drawn in human blood.

• Creating an Angel Banishing Sigil: Requires Human blood or Angel blood.
• Using the Goblet of Blood: Requires fresh blood from a human victim, although animal blood can be used as a substitute. 
• Summoning a demon that was previously exorcised: Requires the blood of the original exorcist. (Repo Man)
• Angel-tracking ritual: This ritual, which Castiel uses to track down Balthazar, requires human blood. (The Third Man)
• Soul-proofing spell: Requires the blood of the soulless person's father - or the equivalent of a father. The father must also be killed. (Appointment In Samarra)
• Summoning Samhain: Requires three blood sacrifices. (It's the Great Pumpkin, Sam Winchester)
• Opening a portal to Purgatory: Requires the blood of a creature native to Purgatory and a virgin. There are several rituals to open Purgatory, and most of them required blood.
• Binding blood spell: Kali used Gabriel, Sam and Dean's blood to cast a spell that prevented them from escaping outside the field/area of her presence (the hotel). (Hammer of the Gods)
• Binding Death: Part of the ritual to summon and bind Death requires the blood of the summoner. (Meet The New Boss)
• Blood Sigil: The blood of the person who's blood relative the spell is seeking is needed for the spell. (As Time Goes By, King of the Damned)
• Curing Vampirism: The ritual to change a newly-sired vampire back into a human requires the blood of the vampire that infected him/her. Also, if the victim has already drunk human blood, the ritual will not work. (Live Free or Twihard)
• Cloaking Flame spell: this spell required blood to be cast.
• Time travel using a blood sigil: Henry Winchester used his own blood to travel into the future and appeared in front of Sam and Dean due to their blood connection.
• Curing Demons: Injections of purified human blood can be used to restore demons' humanity. The blood must be from someone who has recently gone to Confession or blessed.
• Trials of God: The first trial to close the gates of Hell requires that one kill a Hellhound and bathe in its blood.
• Human Body Restoration Ritual: A ritual to restore a demonic vessel that is damaged beyond repair. Requires sigils painted in blood and demon blood to be dripped over the body.
• Binding spell: The caster's blood is required for a binding spell used to trap two beings together such as Dorothy and The Wicked Witch.
• Vampire resurrection ritual: The blood containing the vampire's soul must be dripped over the vampire's remains.
• Opening the Werther Box: Opening the box required a massive amount of blood from a Man of Letters or Legacy, an amount that is fatal without a second person donating their blood.
• Mark of Cain Removal Spell: Requires the blood of the person the caster loves the most.

Weapons

Dead Man's Blood

• Bone of Righteous Mortal Washed in the Three Bloods of Fallen: Requires blood from a Fallen Angel, an Alpha, and the current King of Hell. Once completed can kill a Leviathan.
• Dead Man's Blood: Can be used to incapacitate Vampires.
• Vamp-Tonite: It can kill Vampires, Werewolves, Ghouls, Shapeshifters and other creatures that eat humans, except for Leviathan. (There Will Be Blood)
• Sword of Bruncvik: Forged in Dragon's blood. The only thing that can kill Dragons. (Like A Virgin)
• Leviathan blood is fatal to Angels and possibly other creatures. (Reading Is Fundamental)
• Djinn can only be killed by a silver knife dipped in lamb's blood.
• Veritas could only be killed with a knife dipped in a dog's blood. (You Can't Handle The Truth)
• Chronos could only be killed by an olive stake dipped in the blood of "You don't want to know." (Time After Time)
• Tricksters can only be killed by a stake dipped in the blood of one of their recent victims.
• Sirens can only be killed by a bronze dagger dipped in the blood of someone under their spell. (Sex and Violence)
• Vesta can only be killed by an oak stake stained in the blood of a virgin. (Rock and a Hard Place)

Other uses

Castiel possessing Jimmy Novak

• Angelic Possession: Angels, especially Archangels, typically only possess humans of certain bloodlines, such as the Winchester bloodline. Although this is not necessarily required, as evidenced by Lucifer's possession of Nick, who's certainly not related to the Winchesters, vessels that are not of proper bloodlines will deteriorate over time.
• Croatoan Virus: The virus is passed on through blood contact.
• Food: Certain creatures, namely vampires, vetala, and djinn live off the blood of humans. Some demons, like Lilith, also drink human blood for fun.
• Vampiric reproduction: Humans can be transformed into vampires by ingesting vampiric blood.
• Demon blood is needed to charge the Special Children's powers, as well as for a vessel to contain Lucifer.
• According to Crowley, the blood of a demon could be used for a number of "nefarious spells" against that demon for various harmful purposes, such as Hexing.

See Also

• Demon Blood
• Dead Man's Blood (Object)
• Ruler of Hell's blood
• Fallen Angel's blood
• Alpha's blood
• Vamp-Tonite
• Purified Blood