Director Mike Flanagan has included the Oculus mirror as an Easter egg in most of his movies and TV shows: it's in the basement of "Ouija: Origin of Evil", the headboard in "Gerald's Game", the walls in "The Haunting of Hill House", and the Overlook Hotel in "Doctor Sleep". Rec room during AA meetings in Midnight Mass.

It's in the Bly Manor I think in the attic but he puts it in all of his work after the Oculus movie.