The basic idea is that a world is hit by a certain sort of monsters in enough numbers to tear down civilization. Zombie pandemics and alien invasion seem like the best-documented examples.

Here are a few, simple ideas. Hopefully other posters can further refine them, put them to good use, and/or come up with other interesting concepts in the same vein.

Vampires and/or Werewolves. I've toyed with the idea of running a late 19th or early 20th Century apocalyptic campaign with a vampirism and/or lycanthropy pandemic by analogy with zombie scenarios. Perhaps both? Maybe they're different strains of the same infection, as in the Underworld movies? Maybe it's Dracula's little London jaunt that gets this cataclysm started?

Dragons. I'm also fond of the premise of the Reign of Fire movie — dragon apocalypse! This just begs to be a D&D campaign. Imagine Dragonlance if the bad guys won (or were only stopped late and at a terrible price) and you got to play the grim champions and conquerors of that shattered world.

Demons. The evil cult succeeds in opening a gate to Hell, and fiendish hordes pour forth to annex our home. Literal Hell On Earth. La Divina Commedia meets Mad Max.

The Cthulhu Mythos. The idea that the Old Ones will soon rise and consume all is a recurrent one. While a good case may be made that not much will be left when they do, at least one HPL Mythos piece makes reference to a magic-using human civilization several thousand years in the future. Maybe they've lived through one or more Mythos disaster? Arguably, the Mythos apocalypse is happening in the present of Cthulhutech or even good old GURPS Cthulhupunk.

Giants.

There was some Twilight Meets Matrix film about vampires taking over the world a few years ago.

Giant Insects

Something has caused the insects of the world to grow to giant size. Civilisation is overrun by abnormal flies, ants, locusts and thousands of other giant critters. Livestock is a new food source for some of these critters, forcing flocks underground - where huge scorpions, spiders and worse await.

There is still beauty - giant butterflies and bees pollinate fields of crops and fruit, but man is no longer at the top of the food chain.

What caused the meek to inherit the Earth and can the process be reversed?

Giant Alien octopus things.
Monsters
Six years ago NASA discovered the possibility of alien life within our solar system. A probe was launched to collect samples, but crashed upon re-entry over Central America. Soon after, new life form began to appear and half of Mexico was quarantined as an INFECTED ZONE. Today, the American and Mexican military still struggle to contain "the creatures"...... Our story begins when a US journalist agrees to escort a shaken tourist through the infected zone in Mexico to the safety of the US border.

Something akin to John Carpenter's the Thing would be great.

Roadside Picnic +99

99 years after the alien "visitation" humans, animals and vegetation living near the zones are mutating.


Mist Europa

When the Americans opened a gate to another dimension, they were lucky to get it closed again. The Russians, however were not so lucky with their gate ...


Cloverfield Redux

The northeastern seaboard area is inundated by parasites following the attack.

Take a normally benign race and then take things out of control.

Halflings aggressively ruralizing the land. Coming into conflict with elves and sylvan forest races.

Elves aggressively reforesting the land with a vast increase in predatory plants and animals.

Elemental invasion or using the earth as a warzone.

Dragon Storm has this theme. Mages seeking immortality by draining the souls of dragons and their descendants. Creating mutating storms that trigger those seemingly human and demihuman descendants to change. Huge swaths of land blighted or twisted in the aftermath and all the while blaiming the storms on eeeevil dragons.

Ok, this is ... somewhat specific.

In D&D 3e, werebears are LG. If you are bitten by a werebear, you become tainted, and slowly, inexorably! Become LG.

Now imagine the werebears look at the (fantasy) world and go 'you know what, fuck this. We will have law and prosperity for all.

We just have to BITE EVERYBODY.'


(I originally came up with this contemplating ways you could get paladins to war between themselves)

(or similar. I have heard GURPS Reign of Steel is great for this but do not own a copy.)

Also one can imagine a lot of ways a superhero setting could be given a post-apoc angle. 1) Villains kill all the heroes and take over, 2) superpowered battles become increasingly destructive until they've glassed large portions of the planet, 3) heroes and villains all go God complex insane and enslave humanity, etc

Superman probably isn't much different from a great dragon or demon army when you're a hungry norm searching through the rubble of civilization trying to survive.

In fact imagine a Road Warrior or Fallout-esque wasteland controlled by an evil Justice League, where the pc's dungeon crawl through ruined cities, abandoned superhero bases and forgotten villain lairs in search of lost super-science, magic and alien tech. I think that sounds pretty damn sweet.

The aftermath of a Rust monster population explosion. Dark Sun without the Dark part...

Elves. The noble fey version. You know, all those missing persons every year? They get them. And they keep them sleeping, without aging while dreaming, dreaming dreaming... until it is time for the Sidhe overlords to unleash them and reclaim their dmoination about puny mankind. Besides: they have magic. They are beautiful. They truly want you to believe that it is better to be a slave in their proximity than to be a free man without them. Worse, they might even be right about it.

Pacifc Rim

Spirits of Decadence.

Ennui, apathy, fear-mongering, etc. infect people into not curbing the more self-destructive elements of their civilization until it is too late. A perfect storm of energy, water, food, and other resource scarcity collides with environmental degradation, jingoistic militarism, and population ignorance, leading to an unrecoverable collapse. It's also painfully believable to players, which is a plus.

Quote from: mightyuncle;771073Something akin to John Carpenter's the Thing would be great.

And would probably play out like a Body Snatchers scenario.

For an interesting setting, thr Iron Empires comic series (used as the default setting of Burning Empires, the Burning Wheel SF hack) pits a starfaring human empire and its alien allies against a race of parasites — who use the human bodies and brains they control to build and operate weapons, starships and launch all-out war against the uninfected.

Here's another idea: the Xenomorphs from the Aliens franchise. Now that would escalate quickly.

Quote from: Omega;771126Elemental invasion or using the earth as a warzone.

An "elemental apocalypse" is more or less the plot of World of Warcraft: Cataclysm. Good call. Still, you need to work out a trigger; Cataclysm's was "crazy, ancient, Cthulhu-worshipping dragon breaks free from his prison and rallies rogue elemental lords to destroy the world."

Quote from: Will;771146In D&D 3e, werebears are LG. If you are bitten by a werebear, you become tainted, and slowly, inexorably! Become LG.

Now imagine the werebears look at the (fantasy) world and go 'you know what, fuck this. We will have law and prosperity for all.

We just have to BITE EVERYBODY.'

This is awesome! Though it's up for debate whether a cabal of LG werebears that goes out into the world to forcibly infect everyone are still LG...

Quote from: Raven;771147(or similar. I have heard GURPS Reign of Steel is great for this but do not own a copy.)

Of course! How could I forget about robots. Reign of Steel, isn't that the one in which humans use biotech so robots can't co-opt their weapons?

Quote from: Raven;771148Also one can imagine a lot of ways a superhero setting could be given a post-apoc angle. 1) Villains kill all the heroes and take over, 2) superpowered battles become increasingly destructive until they've glassed large portions of the planet, 3) heroes and villains all go God complex insane and enslave humanity, etc

Shades of Squadron Supreme, Kingdom Come, plus the nightmares of every mutant-hating Marvel X-villain. Fantastic idea. Your post-apoc scenario is pretty sweet too.

Quote from: Beagle;771183Elves. The noble fey version. You know, all those missing persons every year? They get them.

Changeling: The Lost! Only en masse. Maybe with a side of Hellboy 2: The Golden Army if the fey really hate us.

Quote from: Opaopajr;771195Spirits of Decadence.

That's pretty much Werewolf: The Apocalypse in a nutshell.