Early on, one of Brick's thugs comments to Arsenal, "You're that red streak I've been seeing on the news?" Arsenal responds, "Wrong city." This is a reference to The Flash (2014) starring Grant Gustin, whose character was given the nickname, "The Streak" before making a name for himself.
There are three younger versions of characters seen throughout the show: Oliver (played by Jacob Hoppenbrouwer), Tommy Merlyn (played by Arien Boey), Nyssa Al Ghul (played by Taylor Dianne Robinson). Also seen is a younger Malcolm Merlyn, still played by John Barrowman.
First episode to show flashbacks from the perspective of Malcolm Merlyn.