In the scene where Dr. Thomkins is treating two of the arguing circus performers, they are John Grayson and Mary Lloyd. They will eventually marry and have a son Dick, otherwise known as Batman's sidekick Robin.
One of supposed origins of The Joker was that he was the original Red Hood in the 50's.
The relationship between the two families are the same as that of the Hatfield and McCoys two other family rivals who fought over livestock.
David Mazouz (Bruce Wayne) and Cameron Monaghan (Jerome Valeska) have both worked with actress Lucy Fry in separate projects: David worked with her in the movie 'The Darkness', playing Michael Taylor and Stephanie Taylor respectively; Cameron worked with her in the movie 'Vampire Academy', playing Vasilisa "Lissa" Dragomir and Mason Ashford respectively.
Jeremy Bobb, who plays clown Owen Lloyd in this episode, crosses into the Marvel universe when he becomes Gregory Salinger in the final season of Jessica Jones on Netflix.