"Batman: Arkham Knight," like every game in the "Arkham" series, is packed to the gills with Easter eggs and sly references to other characters and events in Batman's world. They're probably one of the best aspects of the series.
However, where "Arkham Knight" differs from the rest is in the substance of all these nods and references. While previous games focused pretty squarely on the wider Batman mythos, "Knight" doubles down on the world outside of Batman, making lots of references to other DC Superheroes and a few other supervillains.
Of course, this isn't a comprehensive list — development studio Rocksteady Games once famously hid a secret so well in "Arkham Asylum" that they had to rat themselves out years later — but it gives a good feel about how other heroes might fit into the world of the "Arkham" games.
Some light spoilers ahead.
There's a great nod to the Emmy-winning "Batman: The Animated Series."
"The Ghost in Gray" posters scattered around Gotham reference the "Batman: The Animated Series" episode "Beware The Gray Ghost," in which it was revealed Bruce Wayne was inspired to become Batman by the fictional Gray Ghost (voiced by '60s Batman Adam West). Years later, the actor who portrayed Gray Ghost returns to the spotlight to team up with Batman and stop the Mad Bomber (voiced by "Batman: TAS" creator Bruce Timm).
It's pretty meta.
The origin of Clayface.
Clayface is a pretty important character in the "Arkham" games, with a fun cameo in "Arkham Asylum" before taking on a bigger role in "Arkham City."
This poster is before all that, though, when he was just a horror movie actor in the classic film "The Terror." His path to villainy would begin when his studio would decide to remake "The Terror"— without him.
The Black Canary has a side gig.
If you watch "Arrow" or "The Flash" on the CW, chances are you might know about the DC superhero Black Canary— she doesn't appear in "Arkham Knight," but this club is named after her — and it's apparently frequented by the poker-card themed villains of the Royal Flush Gang.
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