Continuity mistake: After the cops leave Roger's house, Roger is fighting with the Sandy/demon upstairs, note how the large shotgun hole in her body has suddenly disappeared.
Continuity mistake: When Sandy turns into the demon she's still wearing her own clothes, however her footwear has gone from high-heels to blue socks and white leg warmers. Most noticeable when she gets shotgunned out through the front doors of the house. Then she reverts back to human and is wearing high-heels again.
Continuity mistake: When Rogers blasts the Sandy/demon out through the front doors we see a supposedly large bloody hole in her back, but no blood nor damage to the doors.
Continuity mistake: When Roger digs a hole in his backyard to bury the decapitated body of Sandy/demon he's startled by a neighbour who steps out of his swimming pool. Note the inconsistency of the sweat patch size on his t-shirt throughout this whole scene.
Continuity mistake: In the scene where Sandy visits Roger's house, the 'cross' on her necklace changes position and back throughout the scene.
Revealing mistake: About 27 or 28 minutes into the film, right before the giant creature flies out at Roger through the doorway, you can see the wall (part of a film set) "wobble" for about a half second as Roger opens the door.
Answer: That's the horror movie Don't Look in the Basement (1973), at its own timecode 01:09:30 within that movie.
Super Grover