Many people haved pointed that 'A Song of Ice and Fire' (and particularly the 'A Game of Thrones' TV series) is actually a zombie apocalypse disguised as a fantasy. And that's really a cool way of seeing Westeros. If you really think about it, the wights created by the Others/White Walkers are a good example of 'zombies', even thematically. The way they're used in the TV series represents, with perfection, the themes of death and inevitability usually associated with zombies. They also make you wonder about the futility off all the power struggle going on for the Iron Throne - in the end, when 'the Things in the North' come out, who’s sitting on the throne won't make any difference. In other words, Westeros use zombies in an original and cool way (which is a bless in itself in this zombie-overloaded age).
How about stealing that theme for your favorite campaign/setting? Of course, forget zombies. Also forget undeads. Use orcs.
Yes, orcs. "Real" orcs.
Forget World of Warcraft and other attempts of "sanitizing" orcs. As it happens with all great villains which a long presence in media, orcs were eventually "converted" to a player race (like drows, dragons, demons... even illithids!). Magnanimously ignore this thread. Make yourself a favor and watch again the first minutes of Lord of the Rings - The Fellowship of the Ring. That hungry, bloodthirsty and savage horde plunging directly in the abyss to reach their foes - those are our orcs!
|Picture this... but without elves!|
Orcs are the perfect element for a "zombie" campaign. Players believe they known them. After all, they're just a few Hit Dices with weapons. The classical "cannon fodder" for the Big Bad Boss. So, please, start with orcs that are mechanically identical to what your players are used to. But send them in hordes. Really big hordes. You can even let the players unite a few cities (realms?) to make a beautiful and epic final stand - then throw in all your "George R.R. Martin-powered" sadism on them, sit and watch (and make that last epic battle ends in a perfect "Martin-style" twist if you can… by killing any Aragorn-like NPC!).
After showing them that the “Realms of Man” are doomed, see the party's slow realization that the only way out is retreat. Show them that against the Horde, retreat is ever the only option. This isn't a game about defeating orcs. This is a game about what are you capable of doing to survive the orc apocalypse.
But, please, don't just slaughter your PCs. This is a horror campaign, not an exercise in GM sadism. Once you crush any resistance your players came up, start to probe them, to ask questions: "Now that the World of Man/Free Kingdoms/Waterdeep has fallen… what do you do?" That's the official beginning of your campaign. A good source of inspiration here can be Tolkien's works on Hurin and the Silmarillion legendarium, where we get to see entire lands conquered and controlled by orcs.
Now your players have plenty of – I hope – new and unique challenges. If they still decide to flee, they have to find a safe haven (maybe in the far mythical West, beyond the seas... maybe in the Underdark or inside a very far dwarven kingdom... maybe in oriental lands! etc). If they decide to stay they have to learn to live as the underdog (a good change of roles for a fantasy RPG), maybe going out only during the daylight (that if the orc massive volcanic forges or magic-induced volcanism doesn’t cover the skies in darkness)*.
*And talking about darkness, you have a perfect sword & sorcery setting with an orc apocalypse ready to use - Pathfinder's Golarion during the Age of Darkness.
Or maybe you really want to keep the horror element up in this scenario. Maybe now your PCs have to watch the full scale of extinction as the orcs will probably keeping devouring and bleeding entire races before turning against each other and reducing the entire world to bones and ashes. This second path may be more faithful to the "zombie" mythos (especially if you insinuate that things like eating human flesh can grant you unholy powers, eventually turning humans and demihumans into orcs).
Why in the Nines Hells would any sane player want to play that crucible, you ask? Because it’s different and looks really hard (and your fancy players need a lesson). Because you players are curious (or really thought that Midnight and Dark Sun were “easy settings”). Maybe they want to know how the orcs won or from where they came from. Is it possible to vanquish them? These could be good threads for a slightly different “second season” of this horror campaign.