Maurice LaMarche voices both Mr. Freeze and the Calendar Man in this game. Seeing as this is Julian Day's only voiced appearance in the Arkham games, it makes this trope particularly noteworthy for LaMarche.
Troy Baker portrays both Harvey Dent/Two-Face, and Tim Drake/Robin.
Grey DeLisle plays Vicki Vale and also does Selina Kyle/Catwoman. She would later reprise both roles in Arkham Knight.
Kevin Conroy voices Batman/Bruce Wayne as is standard of him, but also voices Thomas Elliot/Hush, due to Elliot's constructed appearance to make himself look like Bruce Wayne. Like with Grey DeLisle above, Conroy would do both roles again in Knight.
As the generator slams Clayface into the Lazarus Pit and explodes, the vial holding the cure is in Batman's left hand, but when he comes to, it's in his right one. Until Arkham Knight confirmed the Joker died, some people speculated that it was intentional, and the Joker took some of the cure and was faking his death. After Knight, though, it's become clear that it was indeed a screw-up.
In the remaster, the damage to the batsuit completely vanishes during the cutscene where Penguin revives Solomon Grundy.
Development Gag: At one point, Batman overhears thugs talking about the rumor that Harley Quinn used to be a man. Harley Quinn was actually motion-captured by a man, and they even released a fake reveal trailer to tease fans about it.
Robin's is RobinHood.note In his very first appearance, Dick Grayson said his name was "Robin, as in Robin Hood... not robbing hoods!"... hey, it was 1940.
"Vomit vision", (and other similar names) used to describe Catwoman's thief vision by those who dislike her predator gameplay.
God Never Said That: Many have misquoted or misinterpreted Mark Hamill as saying this game will be the last time he plays The Joker. He clarified that what he meant was he wouldn't continue playing The Joker if he felt that he couldn't top his performance, he wanted to leave on a high note. He has since played the Joker again on multiple occasions.
The Other Darrin: Tara Strong replaces Arleen Sorkin as Harley Quinn note as Sorkin had retired as a voice actor by this point, David Kaye replaces Tom Kane as Commissioner Gordon, and Grey DeLisle replaces Tasia Valenza as Martha Wayne. The latter two are perplexing since, as noted above, Tom and Tasia returned from the first game to reprise the respective roles of Quincy Sharp and Poison Ivy.
Nolan North voices both The Penguin and provides the voices of several randomized inmates. It's not unheard of to hear Nolan North berating his Mooks about how much they suck, only to hear Nolan North reply "You heard Penguin! Let's move!"
Hush, who has being-Bruce-Wayne's-evil-double as part of his gimmick, is also voiced by Kevin Conroy.
In an interview, director Sefton Hill said they wanted to include a reference to the infamous Bat-Shark Repellent Spray from the Adam West seriesnote Reportedly, when confronted by "Tiny" in the Iceberg Lounge, Batman would break out the repellent... then open it up to reveal a set of brass knuckles, but ended up nixing it because they felt it was a Level Breaker. There's still a subtle reference; if you get killed by the shark, one of the possible hints reminds you to remember Batman's shark repellent: a flurry of blows to drive it off. In one room, you can listen to the Riddler mutter about ways to take down Batman, and ponders taking Penguin's shark, only to say that there are "too many variables", and that Batman likely has some sort of "shark contingency".
Arkham City was released the same day as Batman: Year One and shares a lot of the same voice talent: Grey DeLisle (Catwoman, Vicki Vale, Stacy Baker, Martha Wayne) is Barbara Eileen-Gordon and Vicki Vale, Steve Blum (Killer Croc and Sickle) is Stan, Fred Tatasciore (Bane, Solomon Grundy and Mr. Hammer) is Arnold Flass and Johnny Vitti, and Danny Jacobs (Victor Zsasz) is Flass's lawyer.