Revealing mistake: At the end when Katie enters Hunter's room and throws Kristi against the camera, Katie's reflection in the wardrobe mirror shows her in a different position from when she attacks Kristi, to after she drops out of view.
Revealing mistake: At the end where Katie kills Kristi by throwing her upwards into the camera mounted on the wall, the reflection of them both in the mirror behind them doesn't match their actual movements. In the reflection, Katie simply pushes Kristi against the wall. She doesn't throw her upwards. (01:30:05)
Chosen answer: It's the demon.
Manky