what is scary movie 4 based on

Scary Movie 4 is a 2006 American science fiction parody film and the fourth installment in the Scary Movie film series). The film parodies several movies, including War of the Worlds, Saw, The Village, and The Grudge). It also spoofs Million Dollar Baby and Brokeback Mountain). The movie is considered the grand finale to the Scary Movie franchise and concludes the story-arc that began with the first film.