A trailer just released on YouTube has revealed the Game of the Year edition of last year's Batman: Arkham City. This is the fairly standard GOTY treatment that has become common place with titles that sell particularly well and amass a large collection of DLC.
The Arkham City GOTY edition will be released on May 29th and will include all previously available DLC (Robin, Nightwing, Arkham City map and skins, and the Catwoman packs) along with the newly announced Harley Quinn's Revenge DLC pack.
It appears that the leaked PS3 Harley Quinn trophies which hinted at this content from earlier this month were legitimate. This will be the final piece of downloadable content released for the game. The content is announced in the announcement trailer below but there isn't much known about the nature of the content. The trophy descriptions seem to hint that the content will be more story based than the previous Challenge Map packs. The Harley Quinn DLC will be released separately on April 30th.