Lucifer's line, "Hail to the king...baby" is an homage to Bruce Campbell's line in Army of Darkness (1992). The producers are fans of Campbell. Previously, Dean has used the alias Ashley J Williams, Campbell's character in The Evil Dead (1981) movies and television series.
In 2012 Danneel Ackles was asked when she'd appear on Supernatural (2005). Her response was "Season 13."
The backdrop of Sister Jo's stage may be the all too familiar, it was a backdrop from the play about Sam and Dean's lives in Supernatural (2005). It also marked as route 66 with a sign that reads "Blackwater Ridge" (from Wendigo (2005)). There is also a crossroads prop onstage pointing to Lawrence (where the boys are from) and Sioux Falls (where Bobby was from, and Jody Mills is the Sheriff)
The painted backdrop on the stage behind Sister Jo ( Danneel Ackles ) during her healing session is from the musical high school production of Supernatural in Fan Fiction (2014), the show's 200th episode The sign post prop points to Sioux Falls, home of Bobby Singer and Jody Mills, and Lawrence, Kansas, the birthplace of the Winchester boys', and the town where their mother Mary Winchester was killed in a fire.