Ghouls are spirits of the dead that traditionally feed on the blood of the dead (with the exception of the ghouls encountered by Sam and Dean), and can only be killed by decapitation or the destruction of their heads. They can shapeshift, appearing human by taking the form of the last person they ate. Ghouls are unaffected by silver or holy water. The only way to kill them is with a head shot, decapitation or extreme head trauma.
The Golem was created in Vitsyebsk, Belarus following the Nazi occupation in World War II, by the rabbis of the Judah Initiative. The Golem was sent to destroy the camp where the Thule Society were carrying out terrible magical experiments on the Jewish people of Vitsyebsk under the direction of Commandant Eckhart. The Golem is taken by Rabbi Bass to America where he eventually bequeaths him to his grandson Aaron Bass. They have superhuman strength, invulnerability, endurance, and longevity. They can be rendered inanimate by removing the scroll from it's mouth.
Hellhounds are aggressive, violent dogs that can and do serve demons in Supernatural. They commonly appear to kill a person who has made a deal with a Crossroads Demon allowing the person's soul to be harvested by hell. In the days proceeding the end of a person's time, they will appear to the victim in dreams. The person will also hallucinate, and be able to see the true face of demons when they are possessing humans. Their origin is unknown. They are also used to hunt down renegade demons and drag them back to hell. They have tremendous strength and speed, can drag human souls to Hell, are invisible to humans unless the person is near death or looking through an object scorched with holy fire, and once they have the scent of a person they won't stop until they catch them. They can be killed a number of ways, using salt, iron nails, and explosives. The can also be killed by "the colt" and an angel blade. They can be kept at bay with Goofer Dust, Devil's Shoestring and salt and can be killed with Ruby's knife.
Kitsunes can take on human form, have claws for stronger defense, are stronger than humans and feed on pituitary glands. Stabbing it in the heart will kill it.
Leviathan, also called the Old Ones, pre-date the creation of humans and angels, as well as the soul itself. They would also pre-date any beings with souls, such as monsters. They are therefore among the first creations of God. They have sharp teeth within an expanding jaw and possess a bifurcated tongue. They can mimic a particular human being following contact with one, or if they obtain DNA from a person. They are then aware of all that person's thoughts and feelings, and even hallucinations. They bleed black goo. Leviathans can possess any human they come into contact with in their fluid form. This person becomes their physical embodiment of sorts. Once a vessel is taken they can reshape it into any human form they touch. They require only a fragment of DNA to transform into a person; even lost hair will do. The creature possessing a little girl takes the form of a doctor by touching his arm. They can also absorb the memories of anyone whose form they take, much like a Shapeshifter, but without requiring the person to remain alive. They are shown to possess greatly enhanced strength.
Leviathans are extremely resilient, surviving multiple shotgun blasts with silver shot, including one to the head at point blank range. One also survived and reassembled itself after being crushed by a falling car. They can even re-attach their heads if decapitated. They can kill angels and in Purgatory Leviathans are able to fly through the air in the form of meteors of black ooze that crash into the ground and take on a humanoid form. Their weaknesses include Blood of the Fallen: The Word of God states that a Leviathan can be killed by a bone of a righteous mortal soaked in the blood of the fallen. There are three fallen whose blood is required; the first of these is a Fallen Angel (Castiel's blood qualifies). The other two Fallen are The Ruler of Fallen Humanity (meaning Crowley, The King of Hell) and a Father of Fallen Beasts (an Alpha). Once this weapon is assembled, the Leviathan only needs to be given a fatal blow to be killed, but it can result in those nearby being pulled to Purgatory with the Leviathan soul. Leviathans are also highly susceptible to materials that contain the chemical compound Borax (Sodium Borate) such as household cleaning products. Contact with their skin results in an instant burning effect that can reduce them to charcoal-like husks if they are exposed to too much. However they will heal from these effects. Removing a Leviathan's head disables them temporarily. But unless the head is kept far away from the body it will re-attach itself. The combination of burning them with Borax and then beheading them and separating the head and the body appears to be the only way to put them down indefinitely, assuming the head has no way of finding its way back to the body. Leviathans also show susceptibility to witchcraft. It can incapacitate them temporarily. Leviathans can be killed by another Leviathan eating them. A Leviathan can even eat itself, a process referred to as "bibbing"(Long one I know!!)
Pestilence is one of the Four Horsemen of the Apocalypse, along with War, Famine and Death. He equates to the Green Horsemen, and wears a emerald-embedded ring. He states that his power is "pure". Pestilence professes allegiance towards War and Famine, showing anger when he learned of their defeat. His ring, along with War, Famine and Death rings form together as a key to Lucifer's Cage. Pestilence is a direct supporter of Lucifer's plan which involves a process which would ultimately result in the extermination of all of humanity. In spite of this, he deliberately attacked Dean and Sam knowing that he was under strict orders not to harm Sam, Lucifer's Vessel. He is also the creator of the Croatoan virus. He is immortal by default. Through his ring he can create/manipulate infestations, plagues, diseases and other sicknesses. He can Teleport wherever he chooses and is indestructible. Removing his ring can make him powerless.
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