The movie is dedicated to Lorraine Warren (portrayed in the movie by Vera Farmiga) who passed away two months before the film's release.
(at around 50 mins) The real Annabelle is at the Warrens' Occult Museum in Monroe, Connecticut, kept in a glass case with warning signs. Unlike the doll in the film, it is a Raggedy Ann doll. In one scene, Judy is watching a game show when a couple win a trip to Vegas and a Raggedy Ann doll. This is a nod to the real Annabelle.
The Ferryman is based on the Greek mythological deity of the same name: that ferries souls across the River Styx to the Underworld, tolled with specific golden coins. The coins also prominently feature as the artifact in the Warren's house that summon the Ferryman entity.
The samurai armor that features in the Warren occult museum is based on Japanese mythology's demonic warrior, the Oni, marking along with the Ferryman the second cultural mythology entity appearing.
James Wan stated that the movie would pick up directly after Ed and Lorraine Warren took the Annabelle doll, in the first Annabelle (2014) movie. Therefore, the movie takes place in the Warren house, along with all the other artifacts.