Felicity's bumbling explanation to Curtis as to why she needs the playing card analyzed is reminiscent of when Oliver first came to her with similar requests at the beginning of his crime-fighting career.
When Ra's al Ghul/Malcolm Merlyn (John Barrowman) warns Laurel (Katie Cassidy) about bringing back Sara, "What you are asking for hasn't been done in ages past. Even then, only in legend." This same quote was used in Star Trek III: The Search For Spock (1984) between Spock's father Sarek (Mark Lenard) and the Vulcan High Priestess, T'Lar (Dame Judith Anderson).
The Dark Archer Theme is used in the soundtrack for the first time since the Season 3 finale.
Neal McDonough and JR Bourne, who play Damien Darhk and Double Down, respectively, have each appeared on Suits (2011), as a lawyer and a client, respectively.
The last name of JR Bourne's character Jeremy Tell/Double Down could be a reference to either the cards he uses as weapons or archery/bow and arrow: a "tell" is a gesture cards players have that gives away what kind of hand they have and William Tell is the fabled archer who was forced to shoot an apple off his son's head. It has a "double" meaning.