They are ghosts, who have had some great wrong done to them in their lives (normally what killed them), this causes them to remain after death, to try and avenge this wrong. Overtime they slowly become obsessed with this until it is the only thing they can think of. Bobby described it like "an itch that you just can't scratch". As such they act violently to try and avenge the wrong, however in the process, their obsession with revenge often leads to them harming innocent people. Sometimes their vengeance can spread on to others, who had nothing to do with them, but have or are doing something that is similar to their death.
It is possible, that once they are avenged that they pass on, however often they are unable to cause this. Occasionally, they're people who are still alive, but on the verge of death.
To kill a vengeful spirit you must find the body, salt and burn it. If the body is already burned then the spirit is possessing an object. Salt and burn the object.
- Peter Sweeney - Takes revenge on those who drowned him and their families, passes over when the final killer gives his life to him, thus avenging him.
- Mary Worthington - Kills people, who are, or believe they are responsible for others deaths, as in her death her killer was never captured. Dispatched when forced to look at her own reflection, as she was responsible for many deaths, forcing her to destroy herself.
- Cyrus Dorian - Takes revenge on those responsible for his death, and their families. Dispatched when lured onto holy ground, thus forcing him leave.
- Jonah Greely - Attacks drivers, as he himself was killed in a car crash. Dispatched when Sam, salts and burns his corpse.
- Father Thomas Gregory - Killed on the church steps, for his keys, returns thinking he was an angel, he went to those who had nothing, and rebuilt their faith, but also had them kill people doing evil deeds. Was put to rest when his fellow father, convinced him to stop.
- Callie - A very powerful ghost, following years of building anger at her father not letting her die, and her not knowing it was her stepmothers fault. As such started bringing the fairy tales he read her to life. Passed over when he accepted the truth, and let her die.
- Sailor’s Ghost - Killed those, who killed their own family, as he was killed by his own brother. Appears every 37 years, to mark his age when he died. He was dispatched, when he attacked the summoned ghost of his brother, causing them both to be destroyed.
- The Witnesses - Raised by the Demon Lilith, they attacked the hunters who failed to save them. They were all dispatched by a spell.
- Dirk MacGregor Jr - A victim of bullying, after being overthrown, he returned and possessed others causing them to attack their bullies. He was dispatched when his last lock of hair was burned.
- Rose Brown - Took revenge on her colleagues, who bullied her in her life and led to her death. Dispatched, after she accidentally killed her sister.
- Jo Harvelle - Made a Vengeful Spirit, by the Egyptian god Osiris, who summoned her from rest and forced her to attack, and try and kill Dean, in a manner similar to her own death. Once Osiris was defeated, she was free from his control and passed on for a second time.
- Other Unnamed Spirits - Summoned by Osiris, to kill those who were declared guilty. They each passed on, once their target was killed.
- Lara Coggins - Left at the aisle on her wedding, she slit her throat, and took revenge on all men who broke women's hearts, by grasping their own hearts and squeezing them, until they died. Was dispatched by Bobby and Rufus.
- Howard's Brother - Summoned, using Howard's own fear based magic, killed his brother, for being partially responsible, for his own death. Passed on after doing this.
- Marin's Brother - Older brother of a young woman named Marin. While originally only haunting his sister, he appeared to become vengeful out of loneliness and began targeting Marin so that he wouldn't be alone. Dispatched after Sam burned Marin's bracelet which he was attached to.
- Bobby Singer - Following his death at Dick Roman's hands, he returned as a spirit, but his anger towards Dick, continued to grow, turning him into a vengeful spirit, unable to control himself he tried to kill Dick, and anyone who got in his way. However his humanity was reached, when he almost managed to kill Sam. Realizing what was happening, he returned to the brothers, and told them to burn his flask, as he knew he would soon lose control again. They did, and he was dispatched.
- Andrew Silver - Killed in a car accident that was the fault of four young college students. Using the Internet to move around, Andrew sought revenge, killing three of the students before his wife, Corey, convinced him to move on peacefully.
- Isabella - A nun who in 1520 fell in love with a man named Piarro who painted her, using her blood and ground up finger in the pigment of the painting. After Piarro rejected her and she found him in bed with another woman, Isabella brutally murdered him and was burned at the stake as a witch. Came to the United States when her things were sent to a church in Massachusetts and began murdering unfaithful men. Put to rest when Sam salt and burned the painting.
- Chester Johnson - A man who was accused of child molestation and accidentally killed by the men accusing him. Came back for revenge by possessing the various costumes he wore in life as a children's performer. Put to rest when Sheriff Donna Hanscum, her deputy Doug Stover, and Sam burned the various costumes.
- Fiona Duncan (original timeline) - The fiancé of Gavin MacLeod she became a vengeful spirit after Gavin was displaced to 2014 by Abaddon and wasn't there to protect her from being brutalized by the crew of the Star. Wished for revenge against teachers as her own teacher had encouraged the crew's treatment of her rather than protecting Fiona. Killed four people before the truth was discovered. Fiona's existence as a vengeful spirit was negated when Gavin returned to 1723 and protected her on the Star. In the new timeline, Fiona's victims were all alive and well.