I watched it about 11 years ago starts with an audition for actors to go into a house to act a reality horror movie only for them to be trapped in a real horror house.
The horror starts with one guy going to the kitchen and getting split into two by a disk coming out of the floor once he opens the fridge door. Later on another guy dies by being impaled into a deer's antler and another's head smashed into a bathroom sink.
The twist at the end is that the girl who survives is actually being used by the monster killing all the people and she had no recollection of it.
She goes back to her normal life, she is a depressed self cutter until the monster asks her to put another ad in the newspaper for more auditions.
I may have misremembered some details but I really need to know the name of the movie.