The 12 best Easter eggs in 'Batman: Arkham Knight'

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.

A little-known Justice Leaguer gets a nod.

The Blue Beetle isn't as well-known as other DC Superheroes, but he's a pretty important player in the DCU. This poster references his alter ego, Ted Kord, the CEO of Kord Industries.

Superman's greatest foe is busy in Gotham.

Probably the most common one on this list, Superman foe Lex Luthor's LexCorp has posters plastered all over the city. Luthor also leaves Bruce Wayne a voicemail.

The Penguin's voice actor gets a shout out.

Oswald Cobblepot, AKA The Penguin, runs a refrigeration company called North Refrigeration. The Penguin is voiced by voice acting extraordinaire Nolan North — who is now a part of the DC Universe.

A cult classic comic gets a makeover.

An old DC Superteam with a paranoid twist, "Secret Six" is a bit of a cult classic, especially under writer Gail Simone's tenure from the mid-2000s to the present.

In "Arkham Knight," there is a pretty glam-looking storefront named Secret 6. While not quite evocative of the actual Secret Six, it is a fun reference for those who love DC lore.

Solomon Grundy live on Broadway.

The imposing (immortal?) villain from "Arkham City" is back, in a brand-new play.

A Batman villain, Copperhead, it out at large.

A DC villain that got reimagined and prominently featured in "Arkham Origins" is still kicking about all these years later. While she's nowhere to be found in "Arkham Knight," you can find a lab where someone's trying to recreate her poison.

Gothamites really want to get out of town.

You'll find a few travel ads scattered throughout "Arkham Knight," with the most recognizable destination being Metropolis — Superman's hometown.

There's a nod to the original Robin's origins.

Even though they have a bigger role in this game, most of their backstory is kicked off to the character bios you can read in your spare time.

This particular poster refers to Nightwing's past. Before he left Batman's side to fly solo in another city as Nightwing, Dick Grayson was the first Robin, a former acrobat of The Flying Graysons that joined Batman as a boy after his parents were killed by criminals extorting their circus.

The Green Arrow is out there, too.

Spotted in the diner of the very beginning of the game is a newspaper with a familiar corporation name.

Queen Industries is run by none other than Oliver Queen, the Green Arrow.

Turns out there are a bunch of DC superheroes that run megacorporations. Funny how that works.