The same exterior building as Paddy's Pub from Its Always Sunny In Philadelphia.
The Thanksgiving murder took place in 1966, presumably a separate event before the Defeo killings in the original film.
Because the filmmakers were going for an "old school" tone and sensibility, none of the visions in the cursed mirror were created with composites or other visual effects. They were all done in-camera with the use of half-silvered mirrors placed at an angle in front of the lens via a process called the "Pepper's Ghost" effect that dates back to stage performances from 1862.