Television last year Share Tweet Pin Share HBO’s Beware the Slender Man Trailer. Coming soon to HBO is the true-crime documentary, Beware the Slender Man. The film follows the true story of two Wisconsin pre-teens who attacked their classmate because of the online Slender Man legend. Two 12-year-olds became obsessed with a Slender Man meme posted to the Something Awful website back in 2014. They lured their classmate out to the woods and stabbed her 19 times. Miraculously, the girl survived, and the two girls who attacked her were found wondering in the wood looking for the Slender Man mansion. The court case is still ongoing. Beware the Slender Man premiers Monday, January 23rd. Watch the trailer.