Mick Davies is saved in Sam's contacts as "Frodo." In Mary's phone, in previous episodes, the viewer sees that he is saved in her contacts as "Hobbits."
After completing a job, Dean held a baseball bat wrapped in barbed wire and said "Dad would love this thing." [EDIT: Dean's actual comment is: "Dad loved this thing."]
John Winchester was played by Jeffrey Dean Morgan, who, at the time this episode aired, was playing Negan on The Walking Dead (2010), a villain famous for using a baseball bat wrapped in barbed wire (called "Lucille").
Cass' FBI name is Solange in this episode. Solange is Beyonce's sister. He used Beyonce earlier in the series.
Dean calls Crowley "Peaches" when speaking on the phone. Peaches is the name of the Devil in the Nickelodeon animated show Rocko's Modern Life (1993).
Crowley says the hellhounds survived because Lucifer (an angel, or agent of God) saved a pregnant one. This mirrors old testament belief that Saul (an agent of God) was commanded to kill all Amalekites and their animals but although he killed the people off he allowed one pregnant animal to survive. This animal was said to be an Amalekite transformed into an animal and, after escaping, repopulated the nation.