Which 1973 horror film is about the demonic possession of a girl named Regan?

What mask does the killer wear in 'Scream' (1996)? What type of mask does Jason Voorhees famously wear? What is the name of the clown in Stephen King's 'It'? In which state is the fictional town of Derry, from 'It', located? Which horror film features a cursed videotape that kills viewers in seven days? In which horror film do characters communicate using sign language to avoid sound-hunting creatures? In which horror film are characters forbidden to look at creatures, so they wear blindfolds? Which 1999 horror film was presented as found footage of three student filmmakers?