The symbols on the device Maya was trying to open resemble the symbols used by the Monitor on the prison of his anti-matter counterpart. This explains why Nash has such a grudge against Mar Novu.
Due to Danielle Panabaker's pregnancy during the shooting of this episode, all her scenes were shot above her waistline and most scenes of Frost fighting were performed by a stunt double.
In the DC comics, Earth 13, which is referenced in The Flash as Earth-13, is an occult Earth of 13-hour days and 13-month years, locked in a perpetual mystic twilight. This Earth is home to Etrigan, rocketed from the planet Kamelot by Merlin, who as Superdemon defends this gothic universe alongside the terrifying supernatural defenders of the League of Shadows.
Sunshine killing the police officers except Joe West and David Singh is quite similar to what Zoom did in Rupture (2016), in which he killed all of the police officers and a news cameraman except for Joe and Singh at CC Jitters for the sake of his affections for Caitlin Snow.
Success is Assured and Liberation were mentioned in the episode. These are episode titles of upcoming episodes of the season.