Over its 15-season run Supernatural provided more than a few scares - but season 1's "Bloody Mary" might remain the series' most terrifying episode. It might only be the fifth episode of the entire series, but it's still considered by critics and fans alike to be among the show's scariest and is one of the most beloved episodes of Supernatural - despite the Winchesters continuing to save people and hunt things for 15 years afterward. On the trail of their missing father, Sam and Dean stumble across a bizarre death in Toledo, Ohio, and soon learn the titular urban legend is to blame.
Even as the brothers investigate, Mary continues to strike, claiming her victims by liquifying their eyeballs and leaving them dead in front of the mirror. Naturally, "Bloody Mary" makes extensive use of the urban legend, which serves as the basis for the story. "Bloody Mary" draws on themes of guilt, with Mary targeting those with a death on their conscience - and given the number of people Sam and Dean kill during the show, it's hardly surprising she sets her sights on the brothers too.
What makes this Supernatural episode so scary is a perfect storm of story and premise. As "Bloody Mary" makes use of an urban legend so widespread it's recognized around the world, it allows viewers to easily understand the concept without the need for any real exposition. This allows "Bloody Mary" a slightly more considered pacing, which is key to building horror in a single 40-minute episode. It also allows more time to show what Mary can do without the need to rush things, making for several suspenseful scenes that linger in the memory.
Mary might not be among the most iconic monsters to appear on Supernatural, but the legend has been striking fear into children for generations; this lends a familiarity to the story that makes it all the more unsettling. "Bloody" Mary's appearance in varied reflective surfaces is achieved using convincing effects, which certainly goes some way towards the episode's lasting reputation. There are times in which Supernatural's use of CGI was less than impressive, but this episode isn't one of them. Seeing Mary crawl out of the mirror also pays an excellent homage to The Ring, but her ability to jump between mirrors and windows is enough to leave anyone a little afraid of their own reflection.
Supernatural season one remains popular for its focus on urban legends, and "Bloody Mary" is quite possibly the most recognizable urban legend there is. However, how it presents the legend is the real reason for the episode's lasting popularity: it's realized using flashy effects, with plenty of tension-building scenes. Sam's guilt over Jessica's death gives the episode a personal edge too, which is why Mary targets him. "Bloody Mary" plays out as a mini-horror movie and showcases just how well Supernatural could carry off traditional scares.