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The game contains several unused character trophies, including Tiffany Ambrose (Roman Sionis' girlfriend), the Batman Inc. Batsuit from Arkham City, and the standard Batsuit from Arkham City.
Contributed by Yoshispacedragon
The 8 assassins selected for the game were chosen for abilities which would challenge the game mechanics. The boss fights were inspired by Arkham City's battle against Mr. Freeze, which tasked players with exploring the full range of Batman's strategies and abilities to overcome the villain.
Contributed by DrakeVagabond
Copperhead's character required three motion-capture actors to animate: a stunt woman, a Cirque du Soleil performer and a martial artist. The game's version of the character"‹ Copperhead was female, instead of the male version from the comics, with input from DC Comics writer Geoff Johns.

This version of the character is also planned to appear in the comics as the new Copperhead.
Contributed by DrakeVagabond
Warner Bros. originally wanted Rocksteady make an Arkham prequel based on the Silver Age of Comic Books, featuring Superman, Wonder Woman, Green Lantern and The Flash. The game eventually became Batman: Arkham Origins, and had less involvement from Rocksteady.
Contributed by DrakeVagabond
Although Rocksteady helped improve the technology, game mechanics and its engine, WB Montréal developed the story independently. The plot was partly inspired by the comic-book series Batman: Legends of the Dark Knight and the graphic novel Batman: Year One, detailing the first year of Batman's career, with Arkham Origins described as a "Year Two" story.

Other elements of the plot were inspired by other Batman stories, such as Batman: The Man Who Laughs, Batman: Turning Points and Batman: The Long Halloween.
Contributed by DrakeVagabond
Early concept art shows that the GCPD were planned to have Martial Artist enemy types. An E3 demo also showed some martial artists working for Anarky.
Contributed by DrakeVagabond
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During the final confrontation with Spoiler:The Joker in Spoiler:the chapel, Spoiler:The Joker is smashed against a stained-glass window, which shatters. In the cutscene following the fight, however, it is fixed.
Contributed by Boyobmas
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At the Arkham Origins panel at Comic Con 2013, it announced that there would be a special reward for players who cleared 100% of the game - a new skin dubbed the "Worst Nightmare" Batsuit. It was to be a physical representation of how Batman's enemies viewed him as a mythical monster at the time. The costume was cut during development, however it does appear in game during cutscenes as how Joker sees Batman.
Contributed by Boyobmas
While investigating Spoiler:Black Mask's supposed murder at Lacey Towers, you can see that one of the rooms belongs to Dr. Penelope Young, a character from Batman: Arkham Asylum.
Contributed by Boyobmas
If you wait long enough during the credits, you can hear Spoiler:Joker singing a variation of Hank William's song: "Cold, Cold Heart" This is also a reference to the later-released DLC with the same name.
Contributed by Boyobmas
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The title screen shown at E3 2013 is different to the one used in the final game.
Contributed by Boyobmas
At the end of the DLC "Cold, Cold Heart", After Batman knocks Ferris Boyle unconscious, he says "Take a seat...Humanitarian." This is a reference to the episode of the Batman Animated Series: "Heart of Ice", which "Cold, Cold Heart" is based on, where Batman says to Boyle at the end of the episode: "Goodnight...Humanitarian."
Contributed by Boyobmas
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In the Blackgate Prisoners side mission, the booking number for one of the convicts is the same number that was given to O.J. Simpson after he was arrested in 1994.
Contributed by Pogue-Mahone
While playing as the Joker in Multplayer mode, if Robin is detected in the area, The Joker will say, "Is it a bird? Is it a plane? No, my bad, it's a bird." This is a reference to the famous Superman tagline, "Is it a bird? Is it a plane? No, it's Superman!"
Contributed by Boyobmas
There is a caged off area in the Royal Hotel level with Christmas decorations and a dead Joker henchman from Batman: Arkham Asylum.
Contributed by Boyobmas
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The Dixon Docks area is a reference to Batman writer Chuck Dixon.
Contributed by DeerBoarDude
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The game appears to use multiple instances of graffiti replicated from actual walls of the developers' city: Montreal, Canada. Specifically, it seems to be all tags by one local artist in particular who uses the tag "Sake".
Contributed by HelpTheWretched