Harley Quinn's Revenge is a story-based DLC available for Batman: Arkham City. It shows the events that happens after Joker's death and how it affected Batman and Harley Quinn, at the point of making her plan a whole operation to get a revenge. It was released to the public on May 29, 2012.
Harley Quinn's Revenge is a story-based campaign where Robin begins the search for Batman, who has disappeared while he was infiltrating Harley's HQ in the Steel Mill trying to free some cops that Harley has kidnapped, after going inside the base, he discovers Batman's Utility Belt. The scene goes back to Batman, a few days earlier, where he infiltrated the building to help the cops. After untying one of them, he gets shot by Harley.
Continuing his search, Robin encounters a giant Joker Statue, made of scrap metal holding a bubble with Batman meditating inside. After examining the device, Robin learns that the bubble is quickly running out of oxygen and learns that Harley Quinn has the only key to release the ball. Robin encounters Harley and several more of her thugs in a dry dock not far away, along with several cops who were taken hostage. After dispatching the thugs and Harley and saving the cops, Robin returns to Batman's prison and is attacked by several waves of thugs, including one Titan thug.
After beating all of the thugs into submission, even the Titan henchman, Robin frees Batman and returns his belt. Harley then reveals over the speakers that she has planted bombs in the building. Batman orders Robin to get the cops to safety and he will deal with the bombs. After successfully defusing the bombs, Batman encounters Harley and several Guardians of Wonder City painted to look like Joker. After destroying the robots, Harley reveals the Giant Joker Scrap Statue was housing a large bomb and was set to go off any second.
After escaping with Harley, Batman can't find Robin and frantically asks Gordon, who was outside Harley's hideout; if he has seen Robin, to which Gordon thought he was with Batman. Fearing Robin was killed in the blast, Batman lets his guard down and begins to mourn. Harley pulls a knife and prepares to kill Batman, however she is stopped by Robin, who not only survived the blast but managed to rescue all of the officers. Realizing Robin is safe (and secretly hiding his relief that his adopted son is okay), Batman tells Robin he is done here and leaves the area. Gordon asks Robin if Batman is okay, with Robin telling Gordon that he will be fine, but in reality knows that Batman is not fine as a worried expression appears on his face.
- On the same day it was released, it was announced that all of the released DLC, including Harley Quinn's Revenge, would be made available as part of the Arkham City Game of the Year edition.
- In the Joker's office in the Sionis Steel Mill, there are countless pregnancy tests scattered around the floor, all reading negative. In the center of the room, there is a baby crib with Scarface inside, painted green and purple to resemble the Joker. This suggests that the depression she suffered after Joker's death cause Harley Quinn to have a miscarriage. A box also mentions that there is a chance for a false positive; possibly rendering the original test moot.
- In the entrance of the Industrial District there is a big plaque saying "Harley's Fun House"