Supernatural - Hell House Season 1 Episode 17

Dean and Sam have to face the ghost of Mordecai who has been living in an old Texas farmhouse. The brothers discover that Mordecai is not a normal spirit, but rather a tulpa, who was created by thousands of people believing in him after the fake legend of him was posted on a popular website. Now, Sam and Dean must stop his spirit from killing any more people who enter the house.