Sam asks Lucifer, "Well, let's say you gank her. Then what?" Lucifer replies, "I dont know, move to LA and solve crimes?" This is a reference to the TV series called Lucifer, based on a character from Neil Gaiman's comic "The Sandman," in which Lucifer takes a vacation from hell and helps cops solve crimes. Billie is also reading a Neil Gaiman book. The series premiered on January 25, 2016, five days after this episode aired!
Misha said during a panel that he was actually very sick whilst filming the scene in which Dean becomes sick from Smiting Sickness.
The music playing in the background during the fight with Lucifer is the same music that was playing in the background when Castiel got his grace back (Season 10, Episode 18: The Book of the Damned)
Lucifer playing Tavares "Heaven Must Be Missing an Angel" may be doubly fitting: according to the bible, Lucifer is "the fallen Angel", so heaven must be missing him, and to the Winchesters with their predilection for classic rock, disco music may very well be "the Devil's music".
When Castiel materializes at the address Dean asked him to come to, Billie the Reaper is reading the Neil Gaiman comic book "Death: The Time of Your Life". It is a spin off of "The Sandman" comic series, dealing with the anthropomorphic personifications of metaphysical entities. The character of Death in this comic series has the task of collecting and escorting those who have died, a task that Reapers similarly perform. In this particular comic volume, a mother strikes a deal with Death to save the life of her son. The bargain is that Death will return at a later date, and the mother will have to take the place of her son by dying. This is ironically similar to the deals that have been made (or attempted) to various Crossroads Demons by Sam and Dean over the course of the series.