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 revenge. It was released to the public on May 29, 2012.
Harley Quinn's Revenge begins with Robin searching for Batman, who has disappeared while infiltrating Harley’s headquarters in the Industrial District to free several cops that Harley has kidnapped. During the search, Oracle confides in Robin that she’s worried about Bruce, who hasn’t been the same since the Arkham City incident and refuses to talk about Talia or Joker. Eventually Robin discovers Batman's Utility Belt, discarded. The story rewinds to two days earlier, where Batman learns from Gordon that Harley has taken several officers hostage. Before Batman leaves, Gordon warns him that Harley still blames him for Joker’s death, and that it could be a trap. Batman rescues one cop from the Steel Mill, who tells him that the others were dragged elsewhere. After attaining location and access codes to Harley’s secret base, Batman infiltrates the shipping yard and attempts to rescue another cop, but is rendered unconscious when Harley attempts to shoot the officer, which Batman intercepts. One of Harley’s thugs removes Batman’s belt, only to drop it when the belt’s countermeasures electrocute him, leaving it for Robin to find.
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 tracks Harley and several more of her thugs to 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 confronts Harley and several Mechanical Guardians painted to look like Joker. After destroying the robots, Harley reveals the Giant Joker Scrap Statue is housing a large bomb and is set to go off any second.
After escaping with Harley, Batman is unable to find Robin and frantically asks Gordon 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 everyone 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 uncertainly telling Gordon that Batman will be fine.
- 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"