This episode features three actors who have all appeared as recurring characters on Lost (2004) - Harold Perrineau, Jeremy Davies, and William Mapother.
The building where John and Ritchie have a conversation is called Bradstreet Hall. It is named for Tim Bradstreet, a comic book artist that did artwork for the comic Hellblazer.
Oglethorpe University in Atlanta is the actual campus used as Ivy university in this episode.
At nine minutes in, the professor is talking on the phone to a student from his office. There is a Mucous Membrane vinyl lp prominently displayed on the right: in the comics this is Constantine's punk rock band from his youth.
Jeremy Davies also appeared in the CW's Arrowverse DC crossover event "Elseworlds" as John Deegan.