The two main characters have the same last names as the two main characters in Resolution, Moorhead and Benson's first movie.
The red substance John and Levi smoke around the 50 minute mark appears to be "The Flower". This is the same substance smoked by Aaron and Anna in Moorhead and Benson's film "The Endless".
The wind chimes heard at the beginning of the film bear a uncanny resemblance to parts of the soundtrack heard in The Endless.