Supernatural has delivered many frightening monsters during its long run. Among those monsters, are ghosts. While it seemed that more ghosts were the subjects of their hunts in the earlier seasons, ghosts still remained a part of their narrative.
While many of the ghosts were frightening, others were sympathetic. Often, the sympathetic ghosts were stuck in limbo for a specific reason like reaching out to a loved one or telling a secret. The majority of the scary ghosts often had been scary humans, and the grave didn't improve their characters. Meanwhile, other scary ghosts held on too long, and their humanity disappeared the longer that they stayed on earth.
10 Scary: Peter Sweeney
Peter Sweeney was a child ghost in Season 1, who had been accidentally killed by other children. Those children hid his bike and put his body into the lake. Decades later, Peter seeks out the other children to kill them.
What made Peter especially scary is that he tried to kill all the family members of the other children. His judgment didn't see shades of gray. All and any family members were considered an enemy.
9 Sympathetic: Kevin Tran
In Season 15, we've been reintroduced to Kevin Tran. Sam and Dean are surprised to learn that their friend and former prophet, Kevin, has been in hell this whole time, being tortured. Since Chuck/God had promised that Kevin would be in heaven, they assumed he was there.
Kevin asks to be released of the demon trap that they created to capture the other demons/spirits, that he can live as a ghost. He tells them that his two options are being sent back to hell where he'll be tortured or living as a ghost, eventually going mad and that he would prefer the latter. Poor Kevin, one of the good guys, we had expected better for him.
8 Scary: Bloody Mary
Another ghost from Season 1, Bloody Mary inhabited a mirror that she had been killed in front of. Though not a horrible human being while alive, the nature of her death and resistance to moving on had made her truly frightening.
Mary would inhabit other mirrors and reflective surfaces, and she'd call out people about their secrets and guilt. Eventually, she'd kill them. She was harsh in her judgment, literally finding fault in anyone.
7 Sympathetic: Callie Garrison
In Season 3, we meet Callie, a literal Snow White, and living corpse. Callie's body has been sustained, but she has been in a coma for a long time. During this time, her spirit has tried to reach out to her father, wanting him to know what happened to her. The poison that she ingested wasn't by accident but done by her stepmother. Since her father doesn't listen to her, she becomes angry. She makes the fairy tales that her father tells her come to life, with dire outcomes.
Once she is able to talk to her father, she stops and lets herself die. It's sympathetic because of her death and how hard she hung on until her father would hear her (and not rationalize her ghost away).
6 Scary: Freeman Daggett
Freeman had been a lonely person who worked as a janitor at a morgue. When he was alive, he stole bodies from the morgue and played with them. As a ghost, he takes this one step further.
He steals live people, forces them to "join" his birthday party, and kills them so that they stay with him forever. Freeman shows that a scary person makes for a very scary ghost.
5 Sympathetic: Molly
In Season 2, Sam and Dean investigate two ghosts that show up during the anniversary of their deaths. One of the ghosts is frightening, but Sam and Dean quickly realize that the other ghost, Molly, doesn't know that she's dead.
Her main worry is her husband as both were in the car when it wrecked. Later, she finds out that her husband lived and remarried. It was she who had died in the wreck. Once she's assured that her husband knew that she loved him, she moves on.
4 Scary: Nurse Dolores Glockner
Another ghost we met in Season 2 is less sympathetic. Sam and Dean help out one of their father's Marine buddies by being thrown into the jail where he works so they can investigate a haunting. People have been dying in mysterious ways.
Sam and Dean discover that it was the ghost of the nurse who was to blame. While alive, she had killed many a prisoner. Dead, she does the same, except with more of a vengeance.
3 Sympathetic: Jo Harvelle
Jo is called back to Dean's trial in Season 7 by Osiris as a witness to Dean's guilt. Dean blames himself for her death and almost wants to be punished for it. However, Jo tells him that she doesn't blame him, still, he feels guilt. Made by a god to punish Dean, Jo says that she doesn't want to do it, but that she has no control.
It was nice to see Jo, albeit briefly, as Jo and Dean were the romantic pairings that was never really able to happen due to Jo's death.
2 Scary: Melanie Merchant
This is probably the scariest ghost, partly because Melanie appeared so innocent. Imagine a young girl's ghost dragging her doll and carrying a razor.
In life, she killed her biological family and her adopted family. In death, she comes out of the family portrait painting and kills anyone who possesses it. She is terrifying!
1 Sympathetic: Bobby
When Bobby dies, he rejects moving on so that he can be there for his boys. Initially, he's attached to his old flask, which Dean carries, and it's humorous in the way he helps. Even while a ghost, he researches for the brothers, points them to the right books and translations. But later, he starts to become a vengeful spirit, possessing a human with little regard to her life. Dean and Sam make the difficult decision to push him away, back into the spirit realm.
As Bobby served often as their father figure and rejected heaven so that he could be with Sam and Dean, our sympathies are in full mode. Bobby was a great character in life and in death, and we miss him.