Red Dead Redemption: Undead Nightmare is an open world, western action-adventure video game developed by Rockstar San Diego and published by Rockstar Games. It was released for the PlayStation 3 and Xbox 360 consoles on October 26, 2010, as a downloadable expansion pack to Red Dead Redemption. The game follows John Marston as he searches for a cure for an infectious zombie plague that has swept across the American Old West. Undead Nightmare is played from a third-person perspective in an open world environment, allowing the player to interact with the game world at their leisure. The player can travel the virtual world, a fictionalized version of the Western United States and Mexico, primarily by horseback and on foot. Hordes of zombies traverse the world, often attacking towns. Gunfights emphasize a gunslinger gameplay mechanic called "Dead Eye" that allows players to mark multiple shooting targets on enemies in slow motion. Two gameplay modes were added to Red Dead Redemption 's online multiplayer mode upon release of Undead Nightmare, allowing up to 16 players to engage in both co-operative and competitive gameplay in a recreation of the single-player setting. Upon its release, Undead Nightmare received generally positive reviews. It won year-end accolades, including Best DLC awards from several gaming publications. A Game of the Year Edition, bundling the game with Red Dead Redemption and all additional content, was released in October 2011.