Supernatural may be over, but fans are still getting treated with new content, whether it be from the prequel series The Winchesters or from the podcast Supernatural Then and Now (hosted by Rob Benedict and Richard Speight Jr., who are determined to help carry on the series' legacy with the help of fans).
In Supernatural, Sam and Dean encountered many terrifying monsters in their travels. However, there were also times in which the Winchesters themselves could have been perceived as the villains - especially when the writers decided to blur the distinctions between good and evil by exploring their darker sides. Although these storylines often created some iconic and memorable episodes, there's no doubt that they sometimes overshadowed the terrifying monsters of the week.
"The Girl Next Door"
Season 7, Episode 3
"The Girl Next Door" is a key episode in Season 7 in which Dean does one of the worst things he's ever done - an action that makes him much scarier than the focus monsters of the episode, a kitsune.
At the end of the episode, Dean confronts the kitsune, Amy Pond, who Sam let live previously. Explaining that she'll just kill again, Dean murders her in cold blood. While this may not seem as scary as it seems, the kitsune really wasn't that scary and seemed almost like a knockoff werewolf. As such, Dean going behind Sam's back and murdering Amy made him look both terrifying and a jerk.
"The Bad Place"
Season 13, Episode 9
Dean's rough demeanor, a personality trait he shares with John Winchester, once again makes him quite terrifying to watch in this episode. During this episode, Sam and Dean find Jack, who is using dreamwalkers to try to reach Mary after he discovers she is stuck in Apocalypse World. But when angels track them down, Dean holds Jack's latest dreamwalker ally, Kaia, at gunpoint and forces her to come along with them and help them.
Although this is to protect her from the angels, the real ones that are killing the dreamwalkers Jack is getting to help him, but that doesn't make Dean any less scary. He's certainly scarier than the angels.
"The Things We Left Behind"
Season 10, Episode 9
Supernatural is clearly one of Jensen Ackles' best roles, and he continues showing off his scary side in "The Things We Left Behind." After rescuing Claire from the humans that have her captive, Dean, who at this point still has the Mark of Cain, is knocked down by the group's leader. What happens next the viewer doesn't see play out, but they are treated to the gory aftermath as Sam, Castiel, and Claire return inside to find all the humans dead.
The scary thing about this is that, though we don't see the fight, the fact that it started and ended in less than a minute, showing off just how strong Dean is with the Mark of Cain - and how scary his violence can be.
"Live Free Or Twihard"
Season 6, Episode 5
Dean's transformation into a vampire in this episode is clearly Sam's fault - and also leads to another moment where Dean becomes much scarier than the monsters in the episode.
After getting turned into a vampire, Dean eventually launches a solo raid on the vampire nest, slaughtering all the vampires within all by himself.
This is an impressive feat if of itself, but Dean's vampiric nature in the episode is frightening, especially when struggles not to go after innocent people and drink their blood, which would make his transformation permanent. Then, seeing his brutal nature in dispatching the vampires all on his own makes him seem far more terrifying than normal.
"Ask Jeeves"
Season 10, Episode 6
While this episode was more humorous and kind of a tribute to Clue, it still leads way to Dean once again showing that he's much scarier than many of the monsters the Winchesters have faced.
The monster in the episode, a shapeshifter, isn't all that scary, and for the most part, the Winchesters aren't that terrifying in the episode either. But the chilling part of Dean comes at the end of the episode, when he kills the shapeshifter and then proceeds to shoot her dead body over and over again. The cold, brutal expression on his face as he shoots her over and over again is quite horrifying to see, especially since everyone knows this brutality is only coming due to the Mark of Cain.
"Slumber Party"
Season 9, Episode 4
Fans will always remember Charlie Bradbury as one of the best side characters in Supernatural, and she played a big role in "Slumber Party," where both Winchesters were shown to be much scarier than the monster.
Towards the end of the episode, the Wicked Witch possesses both Sam and Dean, sending them after Charlie and Dorothy. It's absolutely terrifying to see both Winchester brothers, with green eyes signifying their possession, coming straight at their friends with the intent to kill them. Having the Winchesters act darker and scarier under their own power is one thing, but being forced to be terrifying by the monster they were trying to kill is even scarier.
"The Prisoner"
Season 10, Episode 22
Getting the Mark of Cain was one of the worst things to happen to Dean on Supernatural, and it leads him down a dark and scary path, influencing him to be even more terrifying than usual. A clear case of this happening is in "The Prisoner," where Dean slaughters the entire Styne family after they murdered Charlie.
His rampage alone at the Styne home is scary enough, but what truly makes him terrifying in this episode is his treatment of the remaining Stynes, who have broken into the Bunker. He brutally kills all of them, including the youngest, nicest one and then proceeds to beat Castiel nearly to death when he tries to stop him. It's beyond terrifying and shows just how far Dean has fallen under the Mark of Cain's influence.
"There's No Place Like Home"
Season 10, Episode 11
Dean influence under the Mark of Cain has even led him to harm friends when they attack him, even close friends like Charlie did in this episode.
After Charlie is split into her good side and bad side, the brothers try to help her become whole again by seeing the good side of the infamous Wizard of Oz, Clive Dylan. However, Dark Charlie tries to stop this, and Dean intercepts her, brutally beating her (which also causes pain for Good Charlie). Though the situation is resolved, Dean realizes what he did, and though Charlie forgives him, he can't forgive himself. It's another moment where Dean's brutality scares not only the audience but Dean himself.
"Appointment In Samarra"
Season 6, Episode 11
Dean isn't the only one that can be terrifying; Sam has had his fair share of scary moments throughout the show, especially when he lost his soul and didn't want to get it back. In "Appoint in Samarra," while Dean makes a deal with Death, Sam attempts to kill Bobby so that his soul can never be returned. The two play a game of cat and mouse, but Sam eventually gets the drop on him and would've killed him if Dean hadn't arrived at the last moment.
It's absolutely terrifying to see Sam hunt down his father figure, especially given that this is all because he lost his soul. Soulless Sam is easily more terrifying to see in action given that Sam usually isn't that scary compared to Dean.
"Born Under A Bad Sign"
Season 2, Episode 14
Technically, the scariness of Sam in this episode is caused by the demon known as Meg possessing him, but given that it's still Sam's body, it's still technically a Winchester being scarier than the monster.
In this episode, Sam is possessed by Meg and commits terrible acts, the most terrifying of which being capturing Jo and tormenting her. He then attempts to kill Bobby, but he is subdued and Meg is exorcised from his body. While the episode isn't the scariest Supernatural has to offer, seeing Sam sadistically mess with Jo's head is not a pleasant sight to see, and the episode remains one of the most memorable episodes in the series just for that scene.