The new map features the iconic Arkham Asylum from the DC Comics universe.
It is not to be confused with the 2009 game Batman: Arkham Asylum, with the free DLC map featuring a more comical and exaggerated interpretation of the setting better tailored to multiplayer matches.
Gotham City Impostors received its first free DLC update in February, which added a new map, weapons and costume options.
A second free update in April added another new map and the Bounty Hunter game mode.
Gotham City Impostors was named Digital Spy's 'Biggest Surprise' at last year's gamescom expo.
The Arkham Asylum map is available to download now on Xbox Live, PlayStation Network and on PC.
> Read Digital Spy's Gotham City Impostors review
Watch the Arkham Asylum trailer for Gotham City Impostors below: