In 2014, two Wisconsin girls came to a disturbing decision. In order to appease the “Slenderman,” an internet-sourced boogeyman, they would attempt to murder a classmate. The victim survived, but three lives have been altered forever. Beware the Slenderman explores the intersection where mental illness, social media, and urban mythology collide to result in a horrific crime. It’s available to HBO viewers or as a rental on Amazon for $3.99.