Most of the movie is pretty average when it comes to scares. Some tense moments, some that fall flat, but Satan!Old Lady is scary as shit.
The brief moment where someone strikes a match and we see a mummy-like face behind him - just before Satan/Old Lady fakes her death.
The face of the devil that briefly flashes on the camera early in the film.
We never see the devil kill anyone on screen but we sure as hell can hear it!
One aspect of the film isn't even related to the devil. The security guy sees the guy who killed his wife and son and didn't realize it until hours later.