Batman: Arkham City - 10 Coolest Easter Eggs, Secrets And References Explained

3. Harley Quinn's Pregnancy Tests

Arkham City dangled a lot of potential plot-threads for the sequel, but only one was followed up on in a major way - Scarecrow's return. Hush - who had the potential to be a major villain in the third game - was relegated to minor side role in Arkham Knight, and it seems as though Rocksteady nipped another potential plot thread in the bud before it could become a major thing in their next game.

Approach Joker's Steel Mill office in Arkham City, and you'll actually spot a crib in the middle of a room. There's a Scarface puppet repainted to look like a little Mister J, and some positive pregnancy tests next to them - the implication being, of course, that Harley Quinn was pregnant.

Now, the idea of Joker having a child isn't anything new. In fact, both Arkham City and Arkham Knight pay homage to one of the stories where they "adopt" a new child - Batman Beyond: Return of the Joker. Harley sings Hush, Little Baby in Arkham City's credits, just as she does in WB's animated classic, and Arkham Knight's Jason Todd arc takes the idea of Joker torturing a Robin to breaking point from the same film.

In the end, though, Rocksteady opted not to move ahead with Harley's pregnancy, revealing in Harley Quinn's Revenge that further tests read negative. Arkham Knight did find a different way to continue Joker's legacy though, having him manifest in Batman's inner mind, as well as in the creation of three new proto-Jokers in Johnny Charisma, Henry Adams, Christina Bell and Albert King.