Ray urges Obama to "Run Barry run" referencing the often-repeated phrase used on The Flash (2014) to encourage speedster Barry Allen to run faster.
The episode title "Guest Starring John Noble" refers to the fact that it was in this episode that John Noble made his first on-camera appearance as himself portraying Denethor, the Steward of Gondor from The Lord of the Rings: The Return of the King (2003). For most of the season, Noble's role has been the voice-over artist for the character Mallus. The reason he was chosen by the Legends was that his voice had an uncanny resemblance to Mallus. Noble has made a number of noteworthy performances in the sci-fi /fantasy genre over the years, such as Dr Walter Bishop in Fringe (2008), as well as Sleepy Hollow (2013), Salvation (2017), The Librarians (2014), and The Blacklist (2013).
The Legends get actor John Noble to imitate the voice of Mallus. Noble has portrayed the actual voice of Mallus all season.
Sara told Barack Obama to hold on to his birth certificate, he may need it later. She was referring to a controversy surrounding whether or not he was born in the United States. One of the requirements for becoming President is that a person must be an American citizen and born on US soil, which many disputed in the case of Obama, professing that therefore Obama should be disqualified from the Office of the President of the United States.
The Legends actually met "Lord of the Rings" author J.R.R. Tolkien in season two's "Fellowship of the Spear (2017)".