D&D General Doomsday Weapons?

[Unwise]

My PCs kept missing the hint that the Tribbles they encountered were going to cause an ecological disaster. Time went on and on and they kept ignoring signs of famine as the tribbles destroyed entire ecosystems.

They skipped forward in time about 50 years and went back to their home continent to find it a wasteland just starting to grow back from nothing. Of course, sailors had thought they were cute and taken them to other continents too.

 

[toucanbuzz]

My PCs kept missing the hint that the Tribbles they encountered were going to cause an ecological disaster....

They're trouble.

 

[ccs]

Gives party an Alchemy Jug as part of treasure

DM: one gallon of any liquid...

PC 4: PURE ANTIMATTER!!!

I don't think that's a liquid.

 

[Seramus]

1 Sphere of Annihilation.
1 Core of Planet.
Wait until the oven dings.

 

[Blue]

In a 3.0 campaign I ran, the campaign took a sudden left turn when they found out that a coterie of vampires they were dealing with was attempting to find an artifact orrery that could be used to extend eclipses for arbitrarily long periods of time.

The party eventually found it first, but only because the vampires had been stymied by a mirror that they did not realize was a portal because they had no reflections. Once it was out they were pursued in a desperate trek across the continent to the dwarven homeland that had prisons/asylums carved into stone with a natural anti-magic aura and other protections that they hoped would keep out the vampires.

 

[Dannyalcatraz]

Sphere of Annihilation Bowling Alley

 

[CleverNickName]

You don't need a fancy doomsday weapon, you just need a single wish.

"I wish the sun was only a mile away from Earth."

 

[Dannyalcatraz]

You don't need a fancy doomsday weapon, you just need a single wish.

"I wish the sun was only a mile away from Earth."

I wish all this would just stop.

 

[Baldurs_Underdark]

#1 DM advice: If you don't want it to happen, don't put it into the campaign.

I would never put a real Doomsday Weapon into my campaign because at least 2 of my players are far too
curious and chaotic and would definitely set it off to see what happens. Their characters would most likely die while gleefully cackling and giggling too. (It's an interesting campaign).

 

[Delazar]

In my last Eberron campaign, I had Merrix d'Cannith work together with the lord of Blades to build the Godforged, a contruct dragon powered by a sentient magic item (Xulo). His breath had the power to turn the land into a waste similar to the Mournland, at the same time sucking the "life" out of it to be stored and used later. Their plan was to make Cyre great again (sorry...) while making the rest of the world like the Mournlands. He also made a eldritch machine that could create/destroy manifest zones on nation-wide scale.

In my Spelljammer campaign, I had a solar build connected portals around the sun of Fearun, that would completely deplete the sun, and "transfer" it in the crystal sphere where the solar empire was. Their sun had been destroyed by a previous experiment. He actually succeeded. Faerun was without a sun for 16 days. Then one of the PCs became the new sun... It's a long story.