At one point I had thoughts toward writing an epic level adventure in which a BeholderMage Lich had animated a Kindori (Giant space whale from spelljammer) through the use of "the McGuffin." He tooled around space in this giant whale zombie and filled it with numerous (countless even) undead to serve him in his adventurers.
Well, eventually the McGuffin broke and the whale crashed on a city, enveloping it with its insides. The PC's were called forth to handle what they originally think is a minor undead nusicance, instead to find the entire city crushed and impaling this rotten megalith zombie whale. The BeholderMage Lich has sent out his undead hordes to find replacement "parts" for the McGuffin, and the PC's have to fight their way through the rotten psuedo-corpse to find him and stop him from amazzing another undead horde to take with him back to the outer realms.
Zombies, zombies, everywhere. Infected with some form of space-virus that transmits their condition to those they devour. Come to think of it, this may be my Epic Tier adventure for my current 4th Edition game...