As the final game in the Arkham series, at least before the reveal of Suicide Squad: Kill The Justice League which supposedly takes place in the same universe, Arkham Knight was the last chance Rocksteady had to include references to either their previous games or other DC characters. This resulted in dozens of little nods to both Batman characters as well as wider DC personalities being sprinkled throughout the game.
Many of these can be very easy to miss, especially if you stick to the rooftops as Batman tends to do or are zipping through the streets on the end of the Grapnel Launcher. A lot of them are found hidden away in far corners of the map or can't be seen from the skies.
10 John Constantine
On Founder's Island, on the road under the main part of the city, you can find a ruined street where the majority of buildings are either condemned or abandoned following the evacuation of Gotham City.
One of these condemned buildings is for John Constantine Paranormal Investigator, a character from DC comics who investigates the paranormal and occult. He has been portrayed by both Keanu Reeves and Matt Ryan. Although he can't be seen in person, he was in Gotham at some point before the fear gas threat forced him to leave in the chaos.
9 Toyman
In Ferris Mall, just opposite Pauli's Diner where the fear gas is first released at the beginning of the game, a reference to Toyman can be seen on the outside of the building.
The shop in question, Winslow's Toy Shop, is a reference to Winslow Schott, the alter ego of Toyman who appears to live in Gotham despite normally being a Superman villain. That said, he has come up against the Justice League several times in the past.
8 Kingston Crossroads
Just like in Arkham City, the Black Canary Club returns in Arkham Knight as a reference to Black Canary. However, it is in a very different location this time around and looks completely different compared to the run-down building from Arkham City.
This building can be found on Miagani Island at the crossroads near Kingston on the north-east side of the island. This crossroads is also home to a reference to Solomon Grundy, as there is a theatre show being advertised across the road for a presentation about the undead villain.
7 Queen Industries
On Founder's Island, just across from the Wayne tower, there is a skyscraper currently under construction that you have to rid of thugs partway through the story. This building holds more importance than it lets on.
If you go to the base of the building, the sign reveals that it is the Gotham branch of Queen Industries, the cover for Oliver Queen's luxurious spending as Green Arrow, which is not unlike Bruce Wayne's own company.
6 The Answering Machine
Lucius' office is home to many hidden secrets, including the ability to sneak a peek at the Disruptor before it is actually given to you. Hidden away in the corner of the room is an answering machine with a number of references to DC characters.
Kate Kane, A.K.A. Batwoman, calls Bruce asking if he is going to attend her engagement party and thanking him for his support. Lex Luthor also calls Bruce to try and buy WayneTech from him for a mere one billion dollars.
5 Calendar Man
One of the hardest to find easter eggs in Arkham City involves Calendar Man. He has specific dialogue depending on what date the console clock is set to and will claim to be present at Batman's end if the clock is set to December 13, 2004, the date that Rocksteady was formed.
During the Knightfall cutscene, Calendar Man can be seen among the crowd of reporters just before Wayne Manor is destroyed, fulfilling his promise in the previous game of being there at the end of Batman.
4 Miagani Island
Although there are many small references to DC characters in Arkham Knight, there is one far more obscure reference in the name of one of the islands itself. Miagani Island is a reference to the Miagani Tribe who worshiped the "Man of Bats" in the past. This mysterious person was none other than a time-traveling Batman.
The location of the Miagani Tribe would later go on to become modern-day Gotham. This might explain why there seem to be so many bats in the catacombs under the city, as the people began to worship bats and the Man of Bats as gods.
3 The Long Halloween
While taking part in the Professor Pyg side missions, Alfred will make a note of the killings reminding him of another serial killer he and Batman dealt with who operated on Halloween.
This is a reference to The Long Halloween story, where Batman is tracking a mysterious killer named Holiday while also serving as something of an origin story for Two-Face, who was still just Harvey Dent at the time.
2 Clayface
Inside Panessa Studios, where Batman keeps the civilians infected with Joker's blood, there are several movie posters around the area for a film called The Terror. The lead actor in this film is Basil Karlo, the original Clayface who was the second, healthy Joker in Arkham City and who Batman had to defeat near the end of the game.
There are several other references to the people who would later go on to be known as Clayface, though this one is the most prominent.
1 The Atom
Possibly one of the easiest easter eggs to miss in the entire game is a reference to The Atom. The DC hero, who is currently being played by Brandon Routh on Legends of Tomorrow, is something of a cross between Iron Man and Ant-man.
A locker inside the ACE Chemicals can be found with the name Ray Palmer on it, a reference to The Atom's alter ego. The Atom's signature logo is also painted on the door of the locker.