Every room used in the movie was specifically built and painted to be exactly the way it is seen in the film. Nothing came as is including the lighting and reflections etc.
During filming in "the other world" every crew member was fully covered from head to toe with goop and ooze.
A real working prototype of the "weapon" in the film was built for the movie.
The temperature during filming got well into the 110's so filming all the exteriors ended up being so problematic that only 30 seconds at a time could be filmed and then a 10 min break was needed.
Used in the film is an actual "haunted doll" that is famously moving online and has been documented in a lot of paranormal events.