1x17 Hell House

As a prank, teens spread the word that a local house is haunted by the ghost of Mordechai Murdoch, a man who reportedly killed his six daughters during the 1930s, and it ends up listed on the urban legend website Hell Hound's Lair. When it soon appears that the house actually is haunted, the brothers head to Richardson, Texas, to investigate, and run into paranormal investigators Ed Zeddmore (A. J. Buckley) and Harry Spengler (Travis Wester), owners of the website. Although their research shows no truth in the legend, the brothers nevertheless encounter the spirit, but it is different from what the legend describes. When Sam and Dean realize that the Mordechai's origins on Hell Hound's Lair has also changed, they theorize that the spirit is actually a Tulpa brought on by a Tibetan spirit sigil painted by the teens as a joke, with the beliefs of the website's visitors causing the story to become reality. The brothers trick Ed and Harry into posting a vulnerability for Mordechai onto their website, and later return to the house to kill him. However, Ed and Harry are also there, and reveal that the website's server crashed. With the Tulpa unaffected, Dean decides to burn the house down to stop the entity.