Might as well throw in ninjas and robots while you're at it.
Those are already in game.

As for waves of undead, open your command console and type the following:
player.placeatme 640b7 10
As for multiplayer:
http://www.thenexusforums.com/index.php?/topic/504494-tytanis-skyrim-online-and-skynet-announce-cooperation/