Easter Eggs in Batman: Arkham City

 WARNING: THE FOLLOWING ARTICLE CONTAINS SPOILERS! READ AT YOUR OWN RISK!

• Easter Egg #1: Harley Quinn Pregnant: In the Manager's Office of Joker's Steel Mill is a pregnancy test right beside Harley Quinn's outfit from Arkham Asylum. The test reads positive, hinting that Harley may in fact be pregnant with Joker's child, but in the DLC Harley Quinn's Revenge, there are more pregnancy tests that read negative, excluding one positive sitting next to a box a label on it's side reading, "May provide a false positive." There is also a crib in the office that has the Scarface puppet in it, dressed as the Joker. Here, once again, is a test that states "May provide false positive."
• Easter Egg #2: Joker Singing "Only You": After beating the game on any difficulty, a missed call from Joker plays. In it, the Clown Prince disturbingly sings Only You (And you alone) by The Platters.
• Easter Egg #3: Harley Quinn Singing "Hush Little Baby": After beating the game on New Game Plus Mode, you can hear Harley Quinn singing a distorted version of the lullaby Hush Little Baby. She had previously done this in Batman Beyond: Return of the Joker.
• Easter Egg #4: Secret Coded Messages: After beating the game, using the Cryptographic Sequencer will reveal three separate messages on three various signals and at the end a chime. These numbers can be deciphered with three different methods: The first can be heard on the broadcast 700.00 x, 500.00 y and reads "9 23 9 12 12 18 5 20 21 18 14 2 1 20 13 1 14". It can be decoded via simple Caesarian Cipher, in which A=1, B=2, C=3, etc. The message reads "I will return, Batman." The second can be heard on the broadcast 500.00 x, 900.00 y and reads "5 15 9 7 21 18 18 14 3 5 24 15 12 7 22 3 5 24 15 12 7 22 3 10 5 1 9 22 3 8 25 26 15 16 25 10 15 17 25". It can be decoded in a Caesarian Shift, where the alphabet is shifter down, in this case Z=1, Y=2, X=3, etc. The message reads "You will pay for what you have done to me." The third can be heard on the broadcast 200.00 x, 500.00 y and reads "3 20 26 18 26 16 24 1 11 4 24 9 3 8 5 2 12 18 6 16 7 11 3 10 17 5 13 4 21 8". This is the most difficult to decode, and requires a keyword to translate. By using a Vigenere Cipher with the keyword "Scarecrow" the message will read "Fear will tear Gotham to shreds."
• Easter Egg #5: Killer Croc: After defeating Ra's Al Ghul for the first time, you can find Killer Croc. This is the only opportunity to see him. Instead of following the current objective, go to the easternmost part of the Subway Maintnance Enterence. Once there, throw a Remote Control Batarang through a small hole in the bars and hit the button on the other side. Killer Croc bursts out of the wall, threatens Batman, and returns to the murk.
• Easter Egg #6: Ra's al Ghul Never Dies: After Ra's al Ghul kills himself during his fall from Wonder Tower, he is impaled on the Arkham City sign. After beating the game, his body vanishes and his sword (which used to be inside his chest) is sticking out of the ground.
• Easter Egg #7: Catwoman Alternate Ending: In the Catwoman DLC during Episode 3, you are offered two choices: go and help Batman survive the Joker or escape Arkham City with her loot. If you choose to escape Arkham City, an alternate ending will play. In it, Oracle reveals over a distress signal that Batman and Commissioner Gordon are both dead. She also mentions that Joker has broken out of the megaprison and began a massacre, and that Wayne Manor has been destroyed. The game reverses afterward and allows you to make the correct decision.
• Easter Egg #8: The Lightsaber?: Inside the circuit box Deadshot uses to store his weapons, there is what was once thought a lightsaber, but it is actually a low-res sniper scope
• Easter Egg #9: Lost TV Show: There are several references to the ABC TV show Lost. Mark Hamill, who voiced the Joker, is a huge fan of the show. Additionally, Paul Dini, lead writer of the Arkham games, guest wrote for Lost. In a small speech near the end of the game, Joker makes a reference to the Lost finale. He asks metaphorically, pointing out how it might be disappointing to know all the answers, "So how come it all ended in a church?" Also, in Arkham City, you can often hear thugs saying: "I forget, do they ever explain what the island was?"
• Easter Egg #10: Joker's Secret Message: In the Catwoman DLC, Episode 3, when the game rewinds, a subtle voice can be heard. Reversing the already reversed footage reveals the Joker saying "Thank you for the entertainment, Bats!"
• Easter Egg #11: Crazy Quilt: While tracking the location of the League of Assassins, a unique conversation can be heard. In it, inmates voice their suspicion as to who actually beat Two-Face. One of them mentions seeing Crazy Quilt, an infamous comic relief villain, near the Solomon Wayne Courthouse.
• Easter Egg #12: Scarecrow Fear Gas: In the Riddler's third hostage room, there are canisters of Scarecrow's Fear Gas made famous by their appearance in Arkham Asylum. The tanks bear an uncanny resemblance to the containers found in Arkham West as part of a Riddler Challenge. The same canisters can also be found in Hush's hideout.
• Easter Egg #13: The Duality of Man: At the beginning of the first episode of the Catwoman DLC, a cutscene plays where Two-Face goons locate their bosses' safe behind a painting titled "Cain and Abel: The Duality of Man". In the picture Cain is carrying his murdered brother Abel across a barren wasteland. This is a direct reference to the end scene of Batman carrying Joker's body at the end of the game, symbolizing their opposing but symbiotic roles.
• Easter Egg #14: Scarecrow Thugs?: During Protocol 10, certain thugs can be found on the rooftops that have a bizarre outfit on, resembling the Scarecrow's color scheme, complete with a Scarecrow mask and a black Scarecrow face painted on the back. Many people believe this to be a glitch.
• Easter Egg #15: Fake Joker: When Batman is fighting the "healed" Joker just before the events of Protocol 10, using Detective Vision will reveal the entity he is fighting has no bones. This means that Batman was fighting Clayface the entire time.
• Easter Egg #16: Familiar Faces: As Bruce Wayne is entering Arkham City, he can witness Black Mask by looking to the left of the entrance. There, he is resisting two TYGER guards, who eventually subdue and beat the crime lord. Upon entering Line A, a criminal blocks his path and says that Wayne is 'on his list'. He then makes a gun motion with his hand and chuckles. This is in fact the legendary marksman Deadshot, who hints at his mission in Arkham City. When Bruce Wayne, along with the other political prisoners, are confronted by the mass of screaming inmates, Azrael can be seen watching from a nearby rooftop. This could imply that the Watcher in the Wings knows the Dark Knight's true identity. After rescuing the Medical Staff, there is a man to the left of the Church in a gurney, with bandages on his face and clutching a box. The doctor says that he was a doctor recently transferred there who stashed medical supplies and cut his own face off. This is Hush, who Batman faces later in the game.
  • The area where Black Mask resists the TYGER guards is shown via a hole in the building (from which he escaped from), which serves as a riddle. It is where Sionis Industries was owned. Additionally, in the Museum, his wooden mask can be seen seen in a display case.
• Easter Egg #17: The Stacked Deck: You can see a sign that says Stacked Deck, which is reference from Batman: The Animated Series.
• Easter Egg #18: Commissioner Gordon: In the Cryptographic Sequencer while using the encryption key to hack the TYGER radio, you can hear Commissioner Jim Gordon in the radio broadcast.
• Easter Egg #19: The Ventriloquist: In the Cryptographic Sequencer, you can hear a cop saying that Arnold Wesker, the Ventriloquist, is taking someone hostage.
• Easter Egg #20: Next Arkham: After beating the game, three thugs can be heard in the hallway to the right of the Museum's Torture Room. One thug asks what's next, Arkham County, Arkham Country, or even Arkham World. The other thugs nervously dismiss him saying that they'd have to be crazy to do that.
• Easter Egg #21: Prometheus Dossier: All over Arkham City there are newspaper clippings with the headline "Criminal Couple Gunned Down" and "Boy Watches Parents Die." Mentioned previously in his Arkham Asylum Bio, Prometheus' criminal parents were killed and he vowed vengeance, like an opposite Batman. Interestingly, in Mr. Freeze's GCPD Laboratory, there is a dossier on the wall. It's an old Arkham Medical Examination for Prometheus, saying he passed the tests in November 12th, 1982.
• Easter Egg #22: Rocksteady Developers Arrested: Also in the GCPD building is a flyer of recently arrested criminals. These include Joshua Dahdrai, David Tyndale, David Higgins, Jigar Patel, Noel Chamberlain, and Johnny Armstrong. These are all developers at Rocksteady, the makers of Arkham City and Asylum.
• Easter Egg #23: The Ice Trail: After telling Mr. Freeze the location of his wife, there is an ice trail on the water coming from the GCPD; evidently, he used his freeze gun to make an ice bridge/path to the warehouse with his wife.
• Easter Egg #24: Leslie Thompkins: On a flooded building in the Amusement Mile, there is another sign for the Medical Clinic of Dr. Leslie Thompkins. Thompkins was a colleague of Thomas Wayne and an ally of Batman.
• Easter Egg #25: Black Canary: In several places in Arkham City, a green neon sign for the Black Canary can be found. The Black Canary is one of DC Comic's most famous heroines.
• Easter Egg #26: Where It All Began: In Park Row, you can find behind the Monarch Theatre chalk outlines of where the bodies of Thomas and Martha Wayne were when murdered. You can pay your respects on this spot and find a tape left by Hugo Strange to Batman including a message "It will end where it began. - Hugo Strange"
• Easter Egg #27: DC Universe: During the events of Arkham City, Hugo Strange and Talia al Ghul both mention the cities of Metropolis and Keystone. They are the cities of Superman and the Flash, respectively.
• Easter Egg #28: A Death Foretold: Earlier in the game, when Batman is in the Church steeple with Joker's bombs, Batman can wait until the countdown hits zero. Then Joker tells Batman that "You're going to come and find me, you can't stop yourself can you? Sometimes I wonder if all this is just one of us looking down at the other's corpse, trying to work out what to do next. The only question is; whose body will it be? I know who I'm rooting for!" This level of foreshadowing could suggest that the Joker has an even more sinister plan for the Dark Knight...
• Easter Egg #29: Blueprints: In the first Catwoman mission, there is a side table with a map and a blueprint on it. The blueprint is also shown in the War Room in the museum as well as the GCPD next to the Joker magazine. This blueprint is also found in the secret room in Arkham Asylum on the Warden's desk (room with the map of Arkham City) and in Scarecrow's lair in the elevator shaft in Intensive Treatment.
• Easter Egg #30: Hugo Strange's Hidden Room: If you return to the room where you start the game in the Arkham City Processing Center you will find a door that cannot open, however, if you punch the mirror next to it, it will reveal a hidden room. However, the only thing in the room is a Riddler Trophy, and, on the Xbox 360 version, a Political Prisoner.
• Easter Egg #31: Scarecrow's Secret Room: One of the boats near Funland contains a room in which Scarecrow has been testing his fear gas. A thug can be found strapped to a chair inside. To gain access, use the sequencer.
• Easter Egg #32: Cadmus Labs: In Harley Quinn's Revenge, there is a poster that says Cadmus Labs. Cadmus was a scientific research center located in Metropolis.
• Easter Egg #33: Paul Dini: Before Batman took down two snipers, Vicki Vale says the gun shots are seized in Dini Towers, which it is referenced to Paul Dini.
• Easter Egg #34: The White Knight: In the interview tape with Two-Face, it tells about that day in the courtroom where Two-Face was once, former DA, known as the White Knight himself, before a criminal threw acid at Dent's face.
• Easter Egg #35: Bludhaven: In Arkham City, you will hear thugs saying that if they're going to get out of Arkham City, they will leave Gotham and go to another city known as Bludhaven, Nightwing's new home. After solving the Falcone poster as a riddle, it tells the story that the Falcone family fled Gotham and moved to Bludhaven.
• Easter Egg #36: Toyman: In Harley Quinn's Revenge, one of the thugs says that they are going to sell Batman's utility belt to the Toyman. Toyman (Winslow Schott) is an enemy of Superman, and uses toy-based gimmicks for his crimes.
• Easter Egg #37: Abramovici Twins Reunited: If the Steel Mill is revisited after the game's story is complete, the Abramovici twins can be seen and heard, having apparently settled their differences. This is used to solve a riddle, and is therefore not an easter egg.
• Easter Egg #38: Happy Birthday, Mr. Cobblepot: In the Iceberg Lounge VIP Room, there are signs that say "Congratulations" and "Happy Birthday" that suggest it was Penguin's birthday and Killer Croc is the only one who is invited.
• Easter Egg #39: Ferris Boyle: In the Steel Mill, there's a sign that says Boyle Cryogenics that was already solved as a riddle which may be reference to Ferris Boyle's business, GothCorp. Mr. Freeze mention Ferris Boyle in the Interview Tape with Hugo Strange about his origins that he used to work for GothCorp. Ferris Boyle was a CEO of GothCorp in Batman: The Animated Series.
• Easter Egg #40: The Laughing Fish: You can see a box of tricks that has two similar items, a fish that was similar to the one from Batman: The Animated Series episode "The Laughing Fish" and X-ray glasses the Joker was wearing in Batman: Arkham Asylum.
• Easter Egg #41: Lucius Fox: Fox is mentioned before Batman goes to do the side-mission "Tea Party", when Batman requests the Grapnel Boost and is hinted to have manufactured the cure.
• Easter Egg #42: Holly Robinson: Holly is mentioned in the Interview Tapes of Catwoman, where Hugo Strange threatens Catwoman to kill or arrest Holly in his new prison, Arkham City.
• Easter Egg #43: The Long Halloween: The event is mentioned by Catwoman while talking to Calendar Man, also, in the Maroni's Italian Restaurant there's a note saying "NOTICE CLOSED 14th FEB", where, in the storyline, a group of men working as Maroni's bodyguards were gunned down.
• Easter Egg #44: No Man's Land: The event is mentioned in the story "Seismic Disturbances", where a earthquake had occurred in Gotham and flooded Amusement Mile, and in the Catwoman trailer for the game, you can see a vandalized sign saying "No Man's Land", but the sign was removed from the final game to avoid a direct reference to the comics.
• Easter Egg #45: Jezebel Jet: The Jezebel Center is named after her, that was a love interest of Bruce Wayne and an agent of the Black Glove and approaches Bruce as part of a scheme of the Black Glove.
• Easter Egg #46: Azrael's Message and Symbolism: In the circle made outside the Church, you can see words that say "Well thank you ...ie to tell you the truth it's a sacrifice. I was close to giving up many times and nearly broke up with Amanda over it as well. I ...ate that in each. I would take ... as holiday when our production and activity levels would be high." Also the image in the circle doesn't represent the locations where Batman met him during the game, but if compared to the "No Man's Land" map, it shows some locations, they are: the Cathedral Square, the Reservoir, the Wayne Botanical Garden, the Monolith Square and the South Complex.
• Easter Egg #47: Sarah Gordon: The password used by the undercover cops to identify themselves as part of Gordon's team is "Sarah", this is a reference to Sarah Essen Gordon, the second wife of Gordon, after divorcing with his first wife, Barbara Gordon.
• Easter Egg #48: The Terror: The sign seen outside the Monarch Theatre is for the movie Basil Karlo starred, "The Terror", the title is a reference to the series "Joker's Asylum", where Joker tells a story about Clayface's origins. The names featured in the poster, except Basil Karlo, are people from DC Comics and Warner Bros. they are: Shawn Kittelsen, Victoria Setian, Ernest Zamora and Matthew Mizutani.
• Easter Egg #49: Royal Flush Gang: The Gang is referenced by a shop called "Royal Flush Tobacco" in Wonder Tower Foundations.
• Easter Egg #50: Rocksteady Stores: Most of the store in Wonder Tower Foundations are a reference to the developers at Rocksteady Studios.
• Easter Egg #51: Gentleman Ghost: In a store in Wonder Tower Foundations there's a store called "Gentlemen's Hats & Accessories" with a picture that appears to be Gentleman Ghost.
• Easter Egg #52: The Great White Shark: On a building in Amusement Mile, you can see a building with a sign saying "W WHITE" referencing Warren White, the Great White Shark, you can see a similar sign during the Demon Trials with Ra's al Ghul.
• Easter Egg #53: Batman Begins: During the Demon Trials, you can see in the background a train falling off the rails, similar to the climax scene in the movie "Batman Begins", where Ra's al Ghul dies when the train falls from its rails, stopping him once and for all.
• Easter Egg #54: Cupcakes and Wines: In the Collapsed Streets, there's a fence, if you throw a Remote Control Batarang there, you can find two perfectly clean cupcakes and many bottles of wine around them. 
• Easter Egg #55: Catwoman Extra Dialogue: If the player visits various supervillains as Catwoman during points in the game, unique dialogue and cutscenes play (Calendar Man, Bane, Mr. Freeze, Poison Ivy, Mad Hatter, Mr. Zsasz).
• Easter Egg #56: The Broker: In Scarecrow's boat, there is a note says "Mr. Fine will give you all that you require." In Zsasz's hideout, there are cards on the table which is unlocks a riddle. Oracle contacts Batman and mentions the Broker after completing the final Riddler room.
• Easter Egg #57: Wonder City Guardians: During Protocol 10, if the player enters Wonder City, the mechanical guardians would be stacked on top of another in the center of the streets. After Protocol 10, if the player returns to the streets, the guardians would be gone.
• Easter Egg #58: Jason Todd: If you decide to enter the challenge map Joker's Funhouse as Robin, Joker will ask "Didn't I kill you already?". Near the Batmobile in the Batcave, you can find four tires. This might be a reference when Jason first met Batman, which was him trying to steal the tires of the Batmobile.
• Easter Egg #59: The Dark Knight: In the courthouse, Two-Face shoots Batman in the chest, similar to a scene from The Dark Knight. In both cases, Batman survives and takes down Dent just before he can deal a fatal blow on his target.
• Easter Egg #60: Calendar Man's Secret Message: Setting the consoles/PC date to December 13th 2004 and visiting Calendar man results in special dialogue. The date is when Rocksteady studios was founded.
• Easter Egg #62: Gotham City Model: In Wayne Manor, you can see the model of Gotham City in a glass case.
• Easter Egg #63: Batman Returns: In The Steel Mill, when undergoing the side mission 'Hot and Cold' if the player finally reaches The Boiler Room and then walks to where the upgrade gadget is located they can see in the corner of the room a giant yellow duck. This is reminiscent of the one The Penguin uses as a mode of transportation in Tim Burton's Batman Returns. In Park Row, if the player heads towards the front door of Solomon Wayne's Courthouse, turns around and looks towards the right they will see a billboard. If the player grapples up to the billboard and then looks down they will see a large Cheshire Cat's head stationed. This is another nod to Tim Burton's Batman Returns. The head was seen atop Max Shreck's department stores in the film.