Injustice: Gods Among Us. A confusing listing for the DLC has appeared on the site for a little while now, but Amazon has added a detail page complete with a trailer for the DLC that shows off new zombie skins for the characters, and teases a "zombie mode" that turns all of the game's characters into the undead.
The DLC is based on the "Blackest Night" DC storyline by Geoff Johns, in which a Black Lantern Corps power ring brings back various superheroes, including Batman, from the dead. The DLC is mentioned as an Amazon exclusive preorder bonus, but that doesn't mean it won't be available as a separate purchase sometime in the future. In the meantime, we've contacted Warner Bros. for confirmation and clarification on exactly what this content is.