In it, you and your posse take on waves of the infected, while trying to reach a safehouse survive until the timer runs out. Weapons and ammo must be "chosen wisely" at the outset (though more can be rummaged from coffins) and fallen amigos can be revived, provided you get to them fast enough.
In addition to the trailer, Rockstar has revealed that the DLC will bring with it 12 additional Achievements / Trophies As you fight the deadly zombie plague across the frontier in Red Dead Redemption: Undead Nightmare youll be able to earn 12 new in-game accomplishments on both Xbox 360 (as Achievements) and PlayStation 3 (as Trophies) along the way. Revealed here today are five of them... You'll have to wait until game release to find out what the other seven secret hidden accomplishments are.
Fight off 8 unique players during your reign on top during Land Grab in Free Roam.
MAD MARSTON: THE TRAIL WARRIOR
Attain Rank 5 in all Undead Challenges.
SMOKE THAT SKINWAGON
Make it to wave 15 in Undead Overrun Gametype in Multiplayer.
Have every territory saved at the same time during the Undead Nightmare.
ZED'S DEAD, BABY
Attain 100% Game Completion in Undead Nightmare.
(View full article @ BX below)
..Red Dead Redemption 'Undead Nightmare' multiplayer video (http://slumz.boxden.com/f13/red-dead-redemption-undead-nightmare-multiplayer-video-1436324/)