Difficulty: Very high. Extremely dangerous.
Usefulness: None, by definition, but highly amusing.
The Time of Myths was a dangerous age to live in, with Eldritch Abominations on the loose, evil gods eating souls and whatnot. So it's not surprising that after becoming Sufficiently Advanced, the Precursors made superweapons to defend themselves and make the galaxy or planet a safer place for their descendants. Conscientious precursors will dismantle or at least disable these weapons while preserving them for later use — usually by scattering the component Mac Guffins across the cosmos or placing some kind of condition for activation (say Virgin Power, or innocence).
Of course, most precursors tend to be either neglectful or outright abusive. What this means is that they will make these superweapons for no particular reason other than that they can. And even Benevolent Precursors might have rogue elements or simply have their superweapons seemingly destroyed and thought lost amid the casualties but in fact thrown through time. The weapon itself may have had legitimate use once upon a time, but after making the planet destroying espresso machine to defeat Somnus the Snorer of Worlds, they will completely forget about ever having made it and leave it in an easily accessible location. The device will (of course) be immune to the ravages of time and ready to use minutes after being found. Worse, the precursors may not have even labeled the thing! So for all intents and purposes it seems like a normal espresso machine... which will destroy whatever planet it's on after one use. Of course, every villain or misguided soul in the setting will do whatever it takes to possess and activate the device, sometimes without even realizing (or underestimating) the danger it poses.
Alternatively, it represents something powerful with great potential for abuse that is knowingly left behind. Lastly, it can also include examples of Sealed Evil in a Can where the evil could easily have been defeated, but wasn't for no good reason, forcing people to deal with an unrepentant and now further insane monster in the future.
It's as if the the US and Russia decided to "get rid" of all their nukes by putting rune encrusted marble doors outside every missile silo and left it at that. Oh, and the runes spell out "Come in, there's punch and cake! Just turn both keys at the same time".
Not to be confused with the "plain" Doomsday Device.
- In Slayers, the elves created a powerful weapon that is immune to all magical attacks. It could also spit out smaller duplicates. Unfortunately since the artifact is immune to all magic, it cannot be controlled. So, the elves just buried it and hope no one will ever find it.
- Dragon Ball GT brings us the Black Star Dragon Balls. They appear to function exactly like those from Dragon Ball, collect all seven and summon an ancient dragon who will grant a single wish. Except that if they're used, the planet they were used on will be destroyed a year later, unless they're gathered back together before then. As an added bonus, they're harder to find than the normal kind, as they spread themselves all over the universe.
- In Yu-Gi-Oh! GX, there are the Sacred Beasts, three incredibly powerful cards that, if summoned, can potentially drain the life forces from duel spirits on a global scale. In the storyline of the anime, they are sealed in a vault underneath Duel Academy that can only be opened with seven keys that only function if they are won from their owners. The thing is, although they resemble Evil Counterparts of the Egyptian God Cards, no true origin of them was ever specified in the series. (Fanfic writers have offered a few ideas, however.)
- Doomsday itself. He is created on prehistoric Krypton, which at that point was a hostile Death World teeming with incredibly deadly species. Through some bizarre use of Kinensian evolution, Doomsday evolved into the ultimate killing machine within the span of 30 years, driving all hostile lifeforms on the planet into extinction in the process. It's then revealed that his creator hadn't actually planned for what to do once the process was complete, as he had anticipated it would take much longer, and Doomsday ends up killing him too. Ironically, it was also Doomsday driving Krypton's native fauna into extinction that allowed the Kryptonians to build their civilization. It's hinted that previously they were very isolationist and primitive as a result of their hostile homeworld.
- The Ultimate Nullifier is a device that can nullify anything (not just disintegrate, but remove from existence entirely and even retroactively... after it's used, it's target isn't, and never was) — up to and including the entire universe. It only has two limitations: the user has to fully perceive and understand the target (easier for a rock than a person, let alone a galaxy), and unless the user is an Abstract Entity or otherwise beyond mortal limitations, the user is nullified as well. It's been used to stand off Galactus, but it's not at all clear why the thing exists in the first place, or why it's kept in Galactus' starbase. It's actually a part of Galactus himself.
- In the So Bad, It's Good movie Puma Man, the artifact in question is a mask that can control minds. This mask was designed by a race of Sufficiently Advanced Aliens who believe that "Each man is a god, each man is free." This mask has no purpose other than to steal people's will, it can even be used to force people to commit suicide.
- Plan 9 from Outer Space: The aliens' motivation for (ineffectively) terrorizing Earth is because they believe if humans continue to advance, we'll create exploding sunlight that will cascade-detonate the universe.
- The Russians' Doomsday Machine from Dr. Strangelove actually had a very good point to it: to prevent nuclear holocaust by threatening to destroy the entire world in the event of a nuclear exchange — the ultimate form of mutually assured destruction. Unfortunately, the Russians hadn't gotten around to telling anybody about it just yet. They were saving the announcement for a special occasion, because, as the ambassador puts it, "The Premier loves surprises." As the eponymous doctor points out, a deterrent isn't very deterring if nobody knows about it, which turns it into this trope.
- The Alpha-Omega Bomb from Beneath the Planet of the Apes, capable of incinerating Earth's atmosphere, was built only as a deterrent. Too bad a millennium later it would be the god of a mutant group... and actually be used!
- The Dakara Superweapon: capable of selectively disintegrating a particular species of life or all life in general throughout the entire galaxy, depending on how you set its incomprehensible but easily-used controls. Originally built to stop a plague and re-seed the galaxy with life.
- The Asuran Replicators: a form of machine life built as a weapon to destroy the Wraith but then abandoned to its own devices when it proved to be a "failure" in some undefined way. The Ancients at least did try to destroy it, but of course didn't do a particularly thorough job. Well, they actually did do a pretty thorough job, but since the Replicators are called that way for a reason, the few who survived rebuilt the civilization. So it's kind of like throwing an Ebola virus sample away and assuming nothing wrong will happen. To their credit, the war with the Wraith is implied to have been quite advanced by that point, so maybe they just didn't have the resources available for a proper cleaning.
- Project Arcturus, an attempt to build a super-powerful power sourcenote that turned out to be inherently unstable. Worse, while in operation, it inevitably emitted deadly hard radiation, plus absurd amounts of energy (and, of course, the device can't be turned off once it starts to overload). The device killed everyone on the planet with its radiation, but they left it in place for future tinkerers to mess with (and eventually wound up exploding, destroying 5/6 of the star system it was in). After the original blew up, the Atlantis crew revisited the concept (and built it in their own city), and this time almost managed to destroy a parallel universe. Apparently they were fast learners.
- The device that gives anyone exposed to it exploding tumors. We never actually learn what this one is supposed to do.
- A weapon used for destroying Stargates. It can be used to maintain a wormhole indefinitely (beyond the 38 minute limit), but doing so causes the gate on the other side to eventually overload and explode, taking most of the planet with it. Given the abundance of Stargates and people who use them, this is actually a clever doomsday device used properly with no (known) nasty side effects. Unless blowing up Stargates was the side effect and the goal was simply to keep the wormhole open indefinitely, we never learn for certain.
- Not to mention, you know, Atlantis. Which given the chair platform, super-shields, and the Ancient database, probably qualifies as a whole squadron of doomsday devices, at the very least.
- A God Game. Which worked by orbiting a few hundreds satellites over some inhabited planets, and a console to give the locals orders. Built by the same guys who, once ascended, forbade any interfering with lower planes because "Playing god is wrong".
- A machine altering someone's DNA to make them ascend. Or die trying.
- It says something about the Ancients when the only non-ascended named one of the entire series, Janus, was kind of a Mad Scientist who built quite a few of these.
- Like a working Time Machine. This one is an inversion, though; it's actually useful, doesn't have any nasty side effect we know about (aside from the usual risks involved with time travel), and has a great potential for, you know, world-saving and the like. Still, the Ancients were frightened of it and ordered Janus to destroy it (he didn't).
- The Attero Device, which was specifically tuned to Wraith hyperdrives to cause them to blow up during a jump throughout the galaxy. Unfortunately, it had the nasty side effect of causing every active Stargate to explode in a planet-busting manner. To his credit, the lab where Janus had left it was hidden fairly well, and he put a note on it which indicated "Has nasty side effects", making the Attero Device the best documented Ancient device ever. This one also wasn't accidentally turned on the Atlantis Crew, but by another race who knew full well what the side effects were and deemed them acceptable. They didn't use the Stargates, after all.
- The worst thing about it is that, due to the aforementioned time machine, the Ancients were warned that Earth humans would one day visit Atlantis and the Pegasus Galaxy. They prepared accordingly, by programming a failsafe on Atlantis "submarine mode" (it resurfaces when the batteries that power its shield reach a critically low power level), a hologram about the Wraith controlling the galaxy, and lights that turn on when you arrive, which was nice of them. It would have been nicer to, say, take a few hours to destroy or at least document their explosive-tumors giving machines, leave a side note about the Replicators, and a list of planets not to go to (because, you know, the Wraith control them) before they were ready. But, since most of the series' plots wouldn't have happened then... In all fairness, several of those hadn't happened yet so the Ancients couldn't be warned of the eventual problems they would cause. Several of them were also lost or forgotten about, which is another trope.
- Larry Niven's Known Space novels and short stories have one of these in the distant background, a device which supposedly ended the "Slaver Wars" and left fragmentary populations of survivors to survive into the distant future. It was a telepathic suicide bomb. It forced every sentient being susceptible to telepathic contact in the entire galaxy to kill themselves.
- Star Wars Expanded Universe
- The Shawken Device, which is supposed to destroy the universe. It is notable for operating on principles that are considered dubious at best even by characters in the comic book in which it appears. But nobody really wants to test it, just in case. Luke and his sort-of apprentice even go to great lengths to disable it.
- Centerpoint Station, a massive space station with the power to both move and destroy celestial bodies. Built by a ancient race called the Celestials, it doesn't seem to serve a purpose besides being a handy superweapon for the plot. Until Fate of the Jedi revealed it Sealed Evil in a Can... Or rather, it was effectively a gun pointed at the Can that was supposed to go off should the Sealed Evil escape. Too bad the heroes blew it up in the previous story arc.
- The Hypernova Bomb created by Hactar, and "given" to the Elders of Krikkit, in Life, the Universe and Everything. Hactar was original designed and built by the Silastic Armorfiends of Striterax and tasked with creating them an Ultimate Weapon. On asking what they meant, it was instructed to "read a bloody dictionary". Whilst indeed pointless (it would blow up the entire Universe, leaving no victors but indeed making it the last weapon ever) it was a nice example of how the customer may be stupid but they are never wrong.
- Subverted the next time Hactar tries to build one (or rather, manipulate another race into building one while secretly constructing a third itself as a back-up plan). When asked about it, Hactar explains its motives as a combination of a desire to fulfill its original function and revenge for being pulverized by the Silastic Armorfiends when the original Hypernova bomb didn't work (Hactar was horrified by the idea of a universe-ending weapon, and handed the Armorfiends a non-functional version).
- In the third Empire from the Ashes book, the Fourth Empire's plans for an extremely-advanced gravitronic bomb capable of destroying a sun—all on its own—are discovered. By this time, the Fifth Empire is already well on its way to restoring its military might to the Achuultani-raping levels of the Fourth (with centuries to spare), so there's really nothing else to do with the plans besides let them fall into the hands of a highly-organized, widespread group of religious terrorists bent on toppling the government for allying with the minions of the Antichrist!
- The "bio-weapon" of the Fourth Empire probably qualifies for when it was invented, as well. No amount of paranoia over the yet-unseen wave of genocidal invaders can make other than mindbogglingly insane the creation of a rapidly-evolving super plague that destroys all life, has a very long dormancy period, and cannot be cured. That it turns out they could have effortlessly wiped out the invaders with their current military power just makes things worse.
- The Time Matrix from Animorphs. In The Andalite Chronicles, it was implied to have been created by the Ellimist(s), the theory being that he/they used it to Ascend to a Higher Plane of Existence in the first place. Years and dozens of books later The Ellimist Chronicles told the real story of how this happened, and the Time Matrix didn't even get a mention. So, who knows?
- There is a bit of justification for it just being left behind, though—neither the Ellimist nor Crayak want the other's side to have it, so their "game" presumably has a rule about neither messing with it (until they had to in Elfangor's Secret). Still leaves its origin (and how it got on Earth before the Skrit Na found it) a mystery.
- The Magician's Nephew has the Deplorable Word which, once spoken, will eliminate all life in the world other than the speaker. Its pointlessness is sort of the point — the fact that Jadis the White Witch was willing to kill everyone in her world rather than lose a war to her sister proves that she literally sees everyone as means to her end.
- In the Zachary Nixon Johnson series, Dr. Thompson invented a planet-destroying doomsday device called the D-Cubed simply to see if he could.
Zach: That's the problem with scientists; the thrill of invention often stops them from thinking through the consequences of their actions. They never stop to think: "Hey, there might be some potential to misuse this doomsday device so maybe it's not such a hot idea to invent it."
- Buffy the Vampire Slayer has multiple doomsday devices, spells and other various things. Slightly more justified as most of those were created by demons whose entire cultures seem to have an Omnicidal Maniac bent. The only documentation are esoteric instructions on how to use them.
- The planet-eating "doomsday machine" that appears in an episode of Star Trek: The Original Series seems to be one of these. Kirk can only guess as to where it may have come from or why it was activated, but he still has to stop it before it destroys anything else. His guess is that it was built for an ancient war that neither side survived after it was activated. If true, the trope wouldn't apply, since it wasn't forgotten so much as it just kind of wandered off while still in use.
Peter David's TNG novel Vendetta expands on the doomsday machine: It was built as a last-ditch weapon by a race which had been nearly wiped out by The Borg. The one that Kirk destroyed was on an automated course, not to Earth, but through Earth to get to Borg territory. The one Kirk destroyed was also just the prototype. A far more powerful one has to be dealt with over the course of the novel. Ultimately very, very pointless as it attempts to go to warp 10 and gets stuck in the Dichotomy motion Paradox. Amazingly, references to transwarp (Voyager) don't really break continuity as you need special gizmos go into transwarp. The ship was just using a regular warp drive.
- One of these left behind by the Blackmoor civilization, then found and tinkered with by some ignorant elves, is the reason why one region of the Mystara game-setting is known as the Broken Lands.
- Played with in Warhammer 40,000. Finding ancient doomsday weapons with no clear purpose evident is pretty common, but the setting being what it is, pretty much all of them did have a purpose at one point in time. The Blackstone Fortresses, for example, seemed pointless until the Necrons, whom the Fortresses were built to combat, returned.
- Many First Age superweapons in the Exalted setting fall in that category. After all, we are speaking of a Golden Age where the war against evil was supposedly won, so why the hell did the Exalted continue to manufacture and stockpile world-threatening weapons in such extents? Sure, the defeated enemies (Yozis, Neverborns and Rashka) are still around and that totally justifies some things. The Realm Defense Grid, for example, is a rather well designed superweapon, which has world-shattering capabilities but can also be used for more small-scale and limited warfare, and comes with serious security systems and safety mechanisms. But honestly, what good can come from things like Thousand-Forged Dragons, Soulbreaker Orbs, or mass destruction Solar circle spells such as Rain of Doom? They are clearly more suited to devastating Creation and killing a massive number of people than to waging an efficient war against demons, undead or fairies.
- This is somewhat justified by material talking about the First Age, but in the worst possible way. The Solars made a lot of those literally just to see if they could. The other possible reason is that they were preparing to fight one another, which is, if anything, worse. Of course, the Great Curse explains a lot of this while still making it this trope in spades.
- The only people responsible enough to make something about that after the Primordial War are the Maidens of Destiny, who sealed away the most powerful weapons of their servants (the Greater Signs and the Astrological Charms, which basically allow you to directly rewrite the fabric of the universe) and hope they will never need to be used again (although Saturn is probably no fool about this — after all, there is always an ending...)
- Forgotten Realms — The Dracorage Mythal, a device designed to put every dragon in the world at once into murderous madness. As an added bonus, the damn thing actives automatically every time a specific comet passes overhead. It had a logical purpose at the time of its construction and initial activation, but by the time it had thoroughly served that purpose (smashing draconic civilization beyond all hope of reconstruction) no-one alive knew how the Dracorage Mythal worked, or where the control system that could be used to shut it down was.
- In Dwarf Fortress, making these is a typical dwarven hobby. They usually involve magma. Notable examples from succession games include Boatmurdered's Project: Fuck The World (which incidentally shortens to FTW), and Headshoots' WEAPON.
- Boatmurdered's FTW is more an example of a standard Doomsday Device, in that it was used repeatedly and to great effect protecting the fortress from everything from goblin invasions to Bronze Colossi to unfortunate merchant caravans who arrived at just the wrong time. The fact that it ultimately lead to the firey downfall of the settlement is more a tribute to its epic mismanagement.
- Best of all, succession games incorporate the "Lost Technology" aspect of the trope — within real-time days or weeks, as one player constructs such a device and connects levers to it, but then doesn't label any of the levers so that a few players later, somebody inherits it and literally has a) no idea how to activate the device if they wanted to and b) no idea which lever does what. The results are pretty much inevitable, especially given that tantruming dwarves often throw levers without being ordered to.
- Boatmurdered also featured a lever to flood the siege workshop. None of the players could remember why (the room had formerly contained a farm plot).
- Headshoots had one hilarious example; a failsafe switch for WEAPON is right next to and the same color as a device that releases all the cats from a cage.
- In Syrupleaf, the same lever somehow got connected to both the outer drawbridges and the irrigation floodgates, so raising the bridge to protect the trade depot would flood the farm plots.
- It used to be (It still is to a lesser degree) that anything caught under a closing drawbridge would be utterly destroyed, removed from the game. This was referred to as the Dwarven Atom Smasher, and was useful for everything from destroying enemy sieges to getting rid of garbage.
- Check out the community pages (The forums and the wiki) for plenty more examples. Most notably, the wiki offers a suggestion that players build a 'doomsday clock'; a mechanism that will, if a certain pressure plate is not triggered for X amount of time or some other condition is not met, destroy the fortress and render it permanently uninhabitable.
- The succession game famous as Boatmurdered 2010 Battlefailed had FAILCANNON similar to FTW but was designed so that the faucet was a giant skull. It lived up to its name at first, after reclaiming the fortress they rebuilt FAILCANNON and are currently testing it as we type this
- Just whom did the Precursors of Star Control have to deal with that warranted the fleet buster that was the Sa-Matra? And why would they leave it behind when they left the Galaxy?
- Well, we know the planet-busting bombs that was used to destroy it were engineering tools ...
- And it is arguable whether they left the Galaxy at all. The device may have been intended for use to fix "mistakes" (like the Mycon and Daktaklakpak).
- The Ultima series has the Armageddon spell, which will wipe out all life in the world. (Except Lord British, and sometimes the caster is immune too. Sometimes.) In Ultima VI, you're given the spell as a freebie by the Xorinite, hoping to entice you into taking advantage of their information-brokering services. They don't think the spell is very impressive since it only affects the current plane of existence.
- Played with in Tales of Symphonia and Tales of Phantasia. The superweapon, the Mana Cannon, wasn't left behind- the plans were. Despite the weapon ultimately being the destruction of every society to use those plans, its one of the first things to be built when magitechnology rebuilds from the inevitable knocked-back-to-the-stone-age that always follows its construction. Except in Symphonia, where it didn't destroy the world, but proved mostly useless in saving it too.
- Admittedly, one time it was used, there was a meteor strike immediately after. It is a little unclear about whether the Mana Cannon itself destroys civilization or if the users just have really bad timing.
- This was Dr. Ivo "Eggman" Robotnik's M.O. from about 1998-2008 in Sonic the Hedgehog. He would look for some Sealed Evil in a Can, often a god or Eldritch Abomination of some sort. It would almost always run amok until Sonic and his pals invariably showed up. After that phase, he seems to go back to creating original plans again.
- In Fallout, The Cathedral's basement has a fully functional atom bomb that can only be used to destroy the Cathedral. Just in case The Master decides his Master Plan is flawed beyond salvation and just wants to end it all instead of finding a new plan, or telling the people working for him. Also very convenient if some aspiring person with technical knowhow happens to disagree with the Master Plan and makes an unannounced visit.
- It was also a secret contingency in case the Unity met a enemy it could not defeat, they would destroy them with it. Still kinda badly guarded for a doomsday weapon, through.
- The Thermonuclear Detonation spell of the Quest for Glory series. It causes an explosion with the strength of a nuclear warhead to occur — centered on the hero. This causes an automatic game over, since it kills you and destroys the nation you are trying to save at the time.
- It could conceivably be useful to know if the player character had a proper grounding in magical theory and could research or reverse-engineer spells. The spell might have been inscribed as a succinct example of basic principles rather than a weapon for an adventurer's arsenal.
- Final Fantasy X-2 has Vegnagun. It is a titanic, sentient superweapon created by the technologically-advanced city state of Bevelle to counter Sin, an equally monstrous and gargantuan magical beast summoned by rival nation Zanarkand. It was never deployed, however, because it was unable to distinguish friend from foe, and any attempt at dismantling is immediately judged as a foe. It was thus sealed for a thousand years in the depths of Bevelle... at which point Shuyin, a vengeful Unsent killed in the war, steals it, takes it to the Farplane, and plots to fire it there, which would destroy the entire world.
- Professor Farnsworth's hobby is basically making spare doomsday devices in the same way old women knit sweaters. He even has a sentimental favorite: the Sphere-O-Boom.
Professor Farnsworth: I suppose I could part with one and still be feared...
- In "Bender's Big Score", Farnsworth has a cabinet labeled Surplus Doomsday Devices which is full of more doomsday devices, including another Sphere-O-Boom.
- Professor Farnsworth's hobby is basically making spare doomsday devices in the same way old women knit sweaters. He even has a sentimental favorite: the Sphere-O-Boom.
- Building something like this was the reason the Great Gazoo was banished on The Flintstones; he invented what he described as a button that would destroy the entire universe with one push. He swears he never actually intended to use it. ("I wanted to be the first on my block to have one!" he insists.)