It's been known that Zombies Mode would be returning to Call of Duty: Black Ops II, but Treyarch has promised some new surprises. Specific details have still not been made available, but we have a teaser trailer and a date when all will be revealed.
From previous rumors and interviews, it looks like Zombies will see it's own single player or co-op campaign. Whether or not this is all new content or modified versions of the regular single player game are unknown. Here are some details about Zombies development and a comment that suggests we'll see an 8-player Zombies Mode:
Treyarch's Mark Lamia: “[We have given the] zombie team free reign to do pretty much whatever they want with the mode regardless of the direction the campaign is headed in… It’s a totally different frame of mind when you sitting down to play zombies. It’s you and your friends and its coop and it’s blasting Zombies….Black Ops II has the most ambitious zombies that we have ever created. If you ask zombies players what they want, they want more zombies. They are going to get that, more game modes and more ways to play it,”
“The multiplayer engine can throw around twice as many shambling corpses at once, and it can handle a co-op tally double that of Black Ops 1′s.”