Anything that justifies unleashing the Dirty Pair on a situation.
Lampshaded in Biohazard: "If the terrorists do release experimental bioweapons, this planet will become a sterile desert. Whereas, with the involvement of the Dirty Pair, there is a chance — a remote possiblity — that some people may be left alive. We have to play the odds, gentlemen... God help us." They do indeed stop anyone from deliberately releasing a bioweapon and then drop it accidentally in the last panel.
Those two probably count as a bioweapon by themselves.
Tower Of God: No-one wanted to deal with Viole. To them, he was a villain, the most dangerous enemy. But when Kim Lurker started murdering people, they swiftly resorted to asking him for help.
In Tenchi Muyo! In Love, this happens when the characters are discussing using a particular superweapon that is designed to destroy galaxies and galactic clusters on a being that is maybe 30 ft tall (but extremely powerful). At the beginning of the movie, it's a non option, but by the end things are so bad that they use it anyway, albeit with a huge setup.
Slayers crosses the threshold in three Big Bad situations, just before Lina lets fly with a Giga Slave. Said spell carries a significant risk of ENDING THE UNIVERSE should Lina Inverse lose control of it.
Arguably, given Lina's tendency towards collateral damage, anyone asking for Lina's aid in a populated area also likely qualifies.
Humanity in Gunbuster, once they realized that the SpaceMonsters were coming to Sol, famously resorted to transforming Jupiter into a Moon-sized Black Hole Bomb as part of Operation Carneades: piloting said bomb into the center of the Milky Way, where they would hit the Button. The result was a monstrous implosion that consumed the entire Galactic Core, along with roughly 65% of the Galaxy.
In the sequel, Die Buster with Nono (Buster Machine No.7) gone, the only hope humanity had to defeat the last Space Monster was to use the Earth itself as a weapon.
The JSSDF only authorized the deployment of the Evas when Sachiel took an N2 mine to the face and survived. After the first three Angels, they even funded the construction of their own nuclear-powered Humongous Mecha.
In One Piece, the Buster Call is a villainous version of this. When a situation is so threatening to the World Government that even the slightest leak would cause irreparable damage, the Buster Call is summoned. Ten massive warships essentially glass the target island, wiping out any trace of whatever threat they were called to deal with. They can't be called off, either.
The blueprints for Pluton, passed down through a line of shipwrights. To explain, Pluton is a legendary battleship that could wipe out whole islands in a single shot, one of three relics from a long-lost civilization. So why do the blueprints exist? Because the weapons are still out there, and if some idiot were to find and unleash them, an opposing power would be needed. During the Enies Lobby arc, Franky burns the blueprints, claiming that it would be too dangerous to let them exist if Spandam was going to keep seeking them out. Plus, he just found out that Nico Robin, the only scholar who can decipher the ancient records to find the weapon was less a Woobie, Destroyer of Worlds and more a Broken Bird. It was a gamble, to be sure, as Spandam could just use Robin to get Pluton, but Franky was betting on the Straw Hats saving her from the World Government.
In the Fishman Island Arc, when Hordy Jones reveals more and more of who he is and what he plans to do, the citizens eventually turn to calling on Luffy to stop him. What makes this a Godzilla Threshold is that their resident soothsayer, who is never, ever wrong, predicted that Luffy would destroy all of Fishman Island, not to mention Luffy being an extremely notorious pirate. They still decided that they would be better off with him than Hordy.
Bleach: Yamamoto's power is only unleashed when the Godzilla Threshold is crossed.
During the Battle for Karakura Town, Yamamoto sat out of most of the fighting. When he finally makes his move, it's obvious why. His shikai is capable of destroying the entire protected area of the battle site and killing everyone within it. In an uncontrolled detonation, the shikai is capable of shattering the barriers protecting the human world from the fighting.
During the battle with the Vandenreich, Yamamoto unleashes his bankai which immediately starts sucking the moisture out of the entire bankai's area of effect. It is confirmed that if his bankai is active for too long, the entire world will be destroyed. And this is a passive side effect of activating bankai. The four bankai techniques he reveals cross the threshold even further.
The Central 46 is scared shitless of teachingKenpachiZaraki anything beyond a single kendo lesson. Even fighting on just instincts he can defeat Captains, and they're afraid a trained Kenpachi would be unstoppable if he ever openly rebelled. After the Vandenreich decimate Soul Society's forces, they reluctantly rescind this decision, as their own forces no longer have the strength needed for the coming war.
In Giant Robo: The Day the Earth Stood Still, Chief Chujo is a walking example of this trope; the mere suggestion of him breaking out his powers to use in the fight is enough to send fear and panic through his own allies, most of whom remember "the last time" he used them. When he does, we see that they are justified in their fears.
In Saint Seiya, the Athena Exclamation is taboo. It is a technique performed by three Gold Saints of Athena, who focus their Cosmo into a burst of power as powerful as the Big Bang and deliver it on a single opponent. But by the "Hades" arc, Saga, Shura, and Camus perform it because they figure they are already damned by their alliance with Hades.
Then Athena's loyal Saints use another Athena Exclamation against them because it is the only thing that can stop it. It was claimed that two colliding Athena Exclamations can wipe out the whole universe.
After that the primary issue at hand is that the Magic World is collapsing, and the heroes are pretty much entitled to do anything short of blowing the world up themselves to solve the problem.
In Gao Gai Gar FINAL, we get the Goldion Crusher, used on a sun that is also an infinite regeneration machine keeping alive an evil solar system.
The rise of the Saint's Cradle during the JS Incident in Magical Girl Lyrical Nanoha StrikerS is the only occasion when all five Aces' Power Limiters were removed simultaneously. While objectively speaking, the Aces aren't really much of a danger to anyone except the bad guys, a combination of regulations and office politics prevent Section Six from having unrestrained access to more magical power than Hayate's rank allows her to command, at least until the situation is completely out of hand already.
Invoked with constantly increasing severity throughout Dragon Ball / Dragon Ball Z. One proposed gambit near the end of the series involved convincing every person on Earth to sacrifice donate energy in order to power up a final attack against the big bad.
Although a little drawn out, this is used in a minor way in The Melancholy of Haruhi Suzumiya (2009) at the end of the "Sigh of Haruhi Suzumiya" arc. After Haruhi spends a few days royally screwing with reality during the filming of the culture festival video, Kyon restores reality by making Haruhi read a disclaimer, thus distancing the movie from reality. In the epilogue, Kyon tries to make future events easier by flat-out telling Haruhi the identities of the SOS members(Which was theorized to possibly cause her to rewrite reality on a conscious level), only to be be completely ignored.
This has come up once or twice in Rosario + Vampire when unleashing Tsukune's uncontrollable - and potentially irreversable - ghoul aspect was the only way to give the final beat-down to the current Big Bad.
In Fairy Tail the council declares the events of the S-class arc this, with Lahar saying they'll probably have to resort to using their Kill Sat, the only weapon they have that can effectively take out one of the top three guilds and the Ultimate Evil Zeref. That the area they'd fire down at happens to belong to an be populated by a large portion of the titular guild is something of an unfortunate bonus.
It actually happens several times, the first time being when they do fire the Kill Sat on Jellal's Tower of Heaven in order to destroy it before he can use it to revive Black Wizard Zeref. It backfires horribly when they realize that the Tower of Heaven is actually a giant lacrima, and Jellal was counting on them firing it so he could absorb the energy.
Laharl and Doranbalt invoke a minor one at the end of the Grand Magic Games by freeing Cobra from prison so he could use his Dragon Slayer abilities against Future Rogue's dragons. Minor because Cobra isn't particularly destructive or dangerous, but they risked their careers to do it.
In Muv Luv Alternative Total Eclipse, the US has a backup plan in case of BETA landfall in Alaska called "Red Shift". It involves setting off several hundred hydrogen bombs, which would create a strait and a new line of defense, and allow the US to shore up a new defense line. Unfortunately, this plan would also kill just about anyone living in Alaska at the time, namely the main characters as well as the remnants of the Soviet Union.
This trope happens in the last couple of episodes of Puella Magi Madoka Magica. Walpurgisnacht is busily rampaging around and destroying the city—much like Godzilla. Mami, Sayaka, and Kyoko are dead, and Homura is on the verge of becoming a witch, so Madoka decides to make a dubiously legitimate contract specifically to eliminate all witches despite the risk that the entire planet could be wiped out if things didn't go how she planned. It works out pretty well, but the risk was certainly there, since in a previous timeline, Madoka's own uncontrollable "potential" turned her into a planet-destroying superwitch almost immediately after making a contract.
Against Face-Ripper Sophie, Muhyo summons the Admiral, an extremely powerful envoy that typically requires multiple Executors working together to summon.
Immediately afterward, as Rio has betrayed them and Muhyo is still weak from the previous battle, Muhyo has to take a potentially poisonous tempering elixir from Biko to recover the tempering he needs to fight.
In order to defeat Teeki, Muhyo decides to form a contract with Hades, one of the Six Kings of the Underworld, eliciting shocked reactions from his friends Yoichi and Biko, who don't even think it possible.
In another Hulk related example, during World War Hulk Tony Stark gives his second in command the authority to send the whole of Manhattan into the Negative Zone if things with the Hulk get out of hand. Also from that plot line, they repeatedly attempt to bring in the Sentry to fight the Hulk, and Doctor Strange sees fit to drink in the essence of a universe destroying demon. Both of these options end up making the situation worse.
Doctor Strange has to pull out these options quite a bit. In one memorable multi-part storyline from the late 60's, he went through a whole chain of these; to defeat Dormammu's sister, Umar, he had to free the awesomely powerful demon Zom; to defeat Zom, he had to yank out some of its hair, which spread evil magic all over the world and also summoned the Living Tribunal, who threatened to destroy Earth unless Strange could remove all the evil magic he had unleashed; to gather together all the evil magic, he had to give it all to Baron Mordo, giving him a tremendous power-up; to defeat the empowered Mordo, he had to use an Artifact of Doom given to him by the Obviously Evil entity Nebulos, which gave all the evil power to it instead. Finally, he aided the Living Tribunal in defeating Nebulos, and the Tribunal then declared Earth was safe, ending the chain.
During World War Hulk, Strange could foresee no way to defeat the Incredible Hulk (the other Illuminati had been captured and his own hands were broken), so he let Zom possess him so he could use its power. He then found that it took all his effort and concentration just to hold Zom back from murdering everyone, and Hulk still beat him down.
Large-scale Blackest Night example: the heroes release the Parallax entity and allow it to repossess Hal Jordan. This is the same entity who nearly destroyed the entire universe with Jordan the first time. To be fair, the opposing threat is the godlike Spectre being possessed by multiple Black Lantern Rings which boosted its powers and make it kaiju-sized. Parallax honestly couldn't have made it any worse by that point.
It's implied that this is Commissioner Gordon's attitude toward Batman, at least in the early adventures before they became friends. In a Wretched Hive like Gotham, where crime and corruption are rampant, and you can count the number of good cops and competent authority figures on one hand, letting this weirdo who likes to dress up like a bat and fight crime lend a hand couldn't make things much worse...
Beyond the Doomsday Protocol, there's also how Superman defeated Doomsday in Hunter/Prey - having Mother Box teleport them to the end of time and leaving Doomsday there to let the all-destroying Entropy obliterate him.
In Avengers Assemble, when Thanos shows up on Earth looking for the Ultimate Nullifier, Iron Man calls the president and tells him to invoke the Cosmic Protocols (which are only for when the destruction of the planet is possible; Iron Man calls this "DEFCON 1000"). They then proceed to detonate the atomic core of a helicarrier on top of Thanos, nearly killing the Avengers, certainly killing some of Thanos' lackeys, and barely inconveniencing Thanos.
In Hel On Earth, Superman fears he may have to break his moral code and kill H'el to stop him from trying to resurrect Krypton at the expense of Earth. However, it's Supergirl who kills H'el by stabbing him with a kryptonite shard because it was the only way to save the Earth.
The opening arc of Jonathan Hickman's New Avengers is the discovery of a chain of collapsing universes, which begin when two parallel Earths 'incur' into each other and can be slowed if one of the Earths is destroyed. The Illuminati agree that this crosses the Godzilla Threshold, with a single dissenter who is promptly expelled from the group. But when confronted with the reality of an entire planet of people dying, the Illuminati ultimately realize they can't stand back and let them die.
Nick Fury's worst case scenario plan for if Dr. Doom ever gets too out of hand is to drop the Hulk on one side of Latveria and the Punisher on the other, and see who gets to the middle first.
In the Crossed story arc The Fatal Englishman, the last surviving soldiers in Britain have agreed that the only sane reaction to the Crossed virus is to set off a base full of chemical weapons and hope enough of the uninfected survivors (which they estimate at about 50,000, from a population of 60 million) have access to biohazard gear to rebuild in the aftermath.
In the IDW Publishing ongoing Godzilla comic, Boxer, former SAS soldier and leader of the team that captured most of the kaiju, decides it's time to free the monsters to battle Hedorah, Gigan, Space Godzilla, and Monster X when they appear and attack.
Daemon from the Tamers Forever Series is considered to be such an unbeatable opponent that the Tamers only hope is for Takato to die before Daemon can absorb the power of a god.
The Immortal Game: The Mane Six become so desperate to defeat Titan that Twilight comes up with one final contingency in case the Elements of Harmony fail, or they die before being able to use them. That contingency? Releasing Discord to fight him.
The Stars Will Aid Their Escape: The last time Nyarlathotep emerged in Equestria, Celestia was only able to stop him by calling down the power of the sun and incinerating everything for miles, sacrificing the lives of every pony in the affected area (most of whom were rendered hopelessly insane by Nyarlathotep anyway) in order to stop him from spreading. And all that succeeded in doing was temporarily banishing Nyarlathotep back where he came from — he describes it as having been inconvenient.
The Powers Of Harmony: The use of forbidden Lifeforce magic is considered to be an absolute last resort, due to the fact that it leaves the user an addict who grows more uncontrollable over time. During the War of the Sun and Moon, Libra had to use it to immobilize Nightmare Moon's undying army; his Echo Blair is still carrying that burden a thousand years later.
Imperfect Metamorphosis is what happens when crossing the Threshold is exactly the wrong thing to do, as the different characters implementing their own contingency plans just escalates the situation, going from "bad, but manageable" to almost Cosmic Horror Story levels.
So did Ang Lee's Hulk. They bombed a lake, though, and so there were no collateral casualties. But it was certainly the last available option once Hulk and Banner Dad had unleashed all their rage.
The teenagers in Freddy vs. Jason wanted Jason, the guy that killed 20 of their friends, to win the fight against Freddy— if only because Jason would go back home, since he has no other reason to be in Elm Street.
These kids also save Jason from drowning in a dream. He kills the black girl later.
Perhaps the best example comes from the original Godzilla itself, where the Japanese government decides to deploy Dr. Serizawa's Oxygen Destroyer in Tokyo Bay to kill the monster. The Oxygen Destroyer also kills all other marine life in the bay, but the government considers this an acceptable loss in exchange for killing a monster that's just devastated the city. Serizawa himself is reluctant to even let anyone know about the Oxygen Destroyer's existence, even while Godzilla's rampaging, because he's afraid of how horrible a weapon it might be. He crosses his own Godzilla threshold after a montage of the destruction the monster caused shows him what's at stake — and even then he takes steps to ensure his creation can't be misused.
In Godzilla Vs King Ghidorah, King Ghidorah causes Japan to reach this Threshold. They bring back Godzilla (or so they thought) and juice him with radiation.
Of course After King G is defeated, he starts rampaging too, but if you think about it, the situation didn't really get any worse.
At which point they bring King Ghidorah back to fight Godzilla. Oddly enough, that actually works.
In Michael Bay's first Transformers film; when the Deceptions are closing in on the Allspark, the preferred military solution is to hide the Allspark in the middle of a city - where the Decepticons will have trouble getting to it until large-scale military assistance could be attained and keep them busy while the Allspark was moved to another location.
In Independence Day, the revelation that the aliens' only interest is the complete and total destruction of earth serves as the Godzilla Threshold moment that convinces the president to authorize use of nuclear weapons against the invaders. Naturally, it doesn't work on the intended target, though it completely destroys the already-blasted city below.
Based on a similar scene in the 1954 War Of The Worlds, although note that the ID4 example has the key difference that the WOTW use of Nukes was in a desert while the ID4 attack was in Houston.
Cloverfield: the Hammerdown protocol. Though not explained in the movie, it appears to involve either nuking Manhattan or "merely" dropping multiple superheavy conventional bombs on it. To quote the radio operator, "If you can hear the [air raid] sirens, you're inside the blast zone."
The climax of Galaxy Quest—The Big Bad has killed or fatally wounded everyone on the ship and the ship is hurtling towards Earth and will cause mass devastation on impact. Jason gives the order to activate the secret superweapon, the Omega 13. The problem is, nobody knows what the Omega 13 actually does, since the Galaxy Quest TV show was cancelled before it properly appeared. The two common Epileptic Trees are that it either destroyed all matter in the universe in 13 seconds, or created a 13 second time-warp to the past. Fortunately for everyone involved, it's the latter.
In The Core, the heroes reach the outer core of the Earth and discover that the nuclear weapons they've brought along won't be enough to restart it. In response, the general decides to fire up Project DESTINI to restart the core — which was the very thing that had stopped the core in the first place. The predicted devastation to the Earth's surface would be almost as bad as the lack of a geomagnetic field they were trying to fix.
Aliens has the space marines, with Ellen Ripley in tow, arrive at the colony they are supposed to investigate only to find that said colony has been overrun and the colonists are all monster chow. In the process of evaluating the situation, most of the marines also become monster chow. With the mission screwed and the colony beyond help, Corporal Hicks (now the ranking soldier) declares that they will return to their frigate and "nuke the site from orbit".
The Dark Knight has several scenes musing about how much power is appropriate to stop a threat, citing things like Ancient Rome's ability to grant emergency powers to one man. Over the course of the film, it becomes clear that Batman himself has become the threshold for Gotham's criminal underworld. Their response is The Joker.
Bruce Wayne: I knew the mob wouldn't go down without a fight, but this is different. They crossed the line. Alfred Pennyworth: You crossed the line first, sir. You squeezed them, you hammered them to the point of desperation. And in their desperation they turned to a man they didn't fully understand.
Towards the end of the film, Batman hacks every cell phone in Gotham into a listening device/sonar array. Lucius Fox says it's unethical, and that he's quitting after he uses it. Batman tells him to type in his name when they find the Joker, which turns out to activate the self-destruct option.
The Dark Knight Rises: Towards the end of the film, Batman uses the Bat's weapons with lethal intent, in order to stop a nuke from going off. To a lesser extent, he appears in broad daylight for the first time in the series.
The science facility in The Andromeda Strain is set up to nuke itself if anything gets past the containment seals. The scientists later learn that the energy would only fuel the strain's reproduction, wiping out life on Earth in short order.
Tremors 2: Earl is completely surrounded by Shriekers and is standing in the back of Burt's truck. His response: Set a timed explosive to go off and toss it down in the truck. That 4.5 tons of Burt Gummer approved high explosives, parked in an oil refinery.
Burt (panics): "That's 4 and half tons of high explosives!"
Earl (worried): "Is that not going to be enough?! Please, Burt! Don't tell me that's not going to be enough!"
Burt: "Not enough?! It's... Nevermind! RUN!!! It's goinna be BIIIIIG!!!"
Burt does this with his first remote control Graboid kill.
Burt (into his documentary camera): "Note: 2 pounds of C-4 may be a little..." (piece of gravel from explosion bounces off his helmet) "Excessive..."
In The Incredible Hulk this happens twice. The first is when the army fails to capture Bruce in Brazil, motivating Ross to use experimental super soldier drugs on Emil Blonsky. The second time is when Blonsky becomes the Abomination and starts terrorizing New York, forcing Ross to allow the recently captured Banner to Hulk out and take down the Abomination.
The events of Thor serve as this for the Marvel Cinematic Universe as a whole when Earth plays host to "a grudge match that levelled a small town" between two aliens.
And did we mention that one of those loose cannons is the Hulk?
Banner: So, this all seems...horrible.
Natasha: I've seen worse. [referring to Bruce's last Hulk Out]
Banner: I'm sorry.
Natasha: No, we could...use a little "worse".
Judging by JARVIS' tone (remember, this is the Deadpan Snarker who would be a justified page image if he wasn't an AI), the "House Party protocol" in Iron Man 3 seems to be this. It calls in Iron Leigon, 35 suits of Iron Man armour piloted by JARVIS. It's a lot of firepower, not a lot of precise aim, and it definitely falls under Conservation of Ninjutsu.
In Dirty War, DS Drummer, an otherwise good man who genuinely desires to understand the people he is investigating, tortures a suspect after a dirty bomb is detonated in London. The movie also underlines the uselessness of this strategy as it is documents found in the house, not torture, which leads to the clues that prevent further attacks.
Star Trek Into Darkness: Spock Prime has a vow to never reveal anything of his timeline, to prevent even more disruptions. He considers Khan enough of a threat to break his vow in order to warn the Enterprise.
The Vengeance similarly so outclasses the Enterprise that unleashing the superhuman ex-Evil Overlord on it is actually the best option Kirk and co. can come up with.
Spock Prime crossed it in the first film, too, by saving Kirk's life and revealing information about the future to him, as well as giving Scotty a transwarp formula that would not have been naturally developed for another century, because he considered stopping Nero's genocidal campaign against the Federation to be more important than upholding the Temporal Prime Directive.
The first book, Storm Front, has a minor one. Confronted with a toad demon in a heavy rain that prevents him from making use of his old standby fire, Harry Dresden is forced to try for a lightning spell despite the obvious dangers. Given the number of sequels, it's hardly a spoiler to say that it works.
The second book, Fool Moon, had Harry view his use of the Hexenwulf belt this way, with its possibility of turning him into a mindless feral killer.
In book three, Grave Peril, Harry unleashes a thus-far unseen degree of violence when vampires kidnap his girlfriend. The resulting fire is nearly enough to get him in trouble with the Wizarding Union.
In book seven, Dead Beat, Harry is faced with several necromancers competing for the chance to be the one to perform a dark ritual that makes its performer into a new god by sucking the life from anyone unfortunate enough to live nearby. In order to bypass the protective magical barrier surrounding them, Harry creatively reinterprets the Laws of Magic, and almost literally enacts this trope, by reanimating a frelling tyrannosaurus (it's not human,so he wasn'ttechnically breaking the law).
In book twelve, Changes, after suffering (in something of a personal best) a broken back, a kidnapped daughter, and a host of vampires old enough to qualify as gods in their own right about to perform an effectively unblockable curse that will destroy his entire family, he turns to one of his final options: swearing his allegiance to Mab, the Queen of Air and Darkness. Harry was even desperate enough to consider performing the Darkhallow rite or becoming a Denarian if Mab didn't accept him.
In book fourteen, Cold Days,Harry discovers that, in an as-yet-unused Chekhov's ArmouryDemonreach is a prison created by the original Merlin for thousands of incredibly powerful and malevolent entities, so much so that there is a failsafe in place that will vaporize most of the continent should the prisoners ever escape, and it won't even kill them. All it will accomplish is to slow them down for a while, but that's still the lesser of two evils.
Harry Dresden IS the Godzilla Threshold. For the natural world, once things have deteriorated to the point you look up Wizards in the Yellow Pages, you've crossed the Threshold. For the supernatural world, Harry is widely considered a magical thug, high powered, but with very poor control. A situation dire enough to involve Harry Dresden usually means you've crossed the Threshold. When the necromancers threaten Chicago, the response of the White Council is to send every available Warden, including the Captain - who recruits Harry (a man they have been fearing is secretly a warlock for the last 10 years) the minute they see him.
In the last book, Tavi had to get all of his armies to reach a main battlefield in a few days — moving several hundred thousand almost at the speed of flight. Then Alera warns him that his plan will cause untold weather devastation thousands of years later, he concludes the devastating long term consequences must be borne if anyone in Alera is to survive.
In Stephen King's Under the Dome, the government does everything in its power to free the town of Chester's Mill from its predicament. This includes firing a cruise missile at the invisible dome surrounding the town, then a second missile when the first one fails, using specially modified acid which can melt through two miles of bedrock, despite the possibility that it could set the dome on fire, and then attempting to use a 'pencil nuke', only to have it melt down and kill fifteen people before it could be used. The government continues, trying to build a second pencil nuke, but by that point, things are so bad they finally decide they don't have time.
The Worldwar series about Alien Lizards invading Earth during WWII: Allying with Nazis. Nuking your own cities. Pulling all those Chemical and Biological weapons out. You do horrible things when you are being invaded by Alien Lizards.
In World War Z, the government is so stumped as to how to fight the zombie hordes that they are forced to implement the "Redeker Plan", using large parts of the population as zombie bait to give the government a chance to regroup and plan. And It Worked.
The Laundry has one of these lined up for when CASE NIGHTMARE GREEN (a.k.a, the stars coming right) ensues — SCORPION STARE, a program that loops a basilisk frequency through every CCTV camera in Britain. Similarly, in The Jennifer Morgue, Mo is given access to "a big white one" in the case that the Bond villain wannabe manages to resurrect an ancient Chthonian war god — and is none too pleased to find out "a big white one" is a tactical nuke.
Robert Jordan's The Wheel of Time series: in the War of Power, the good guys constructed the Choedan Kal, two devices (one for use by a male, one for use by a female) that could draw astronomical amounts of the One Power in order to seal the Dark One away in his prison. Later used to cleanse the poisoned male half of the Power during the climax of book 9, Winter's Heart (during which the female Choedan Kal is destroyed). In The Gathering Storm, Rand at first thinks that the male Choedan Kal is the key to defeating the Dark One, but eventually realizes that it won't work. At the end of the book, he destroys it, knowing there may well be another (and better) way to defeat the Dark One this time around.
In David Weber's Out Of The Dark, the alien commander of the forces invading Earth eventually concedes the use of genocidal bioweapons as the only option against a planetful of humans who refuse to submit, and are rapidly depleting the invader's reserves.
In another David Weber work, Honor Harrington, the Havenites cross this threshhold when they realize that the Manticorans' new weapons mean inevitable defeat for the Republic of Haven, and decide to capitalize on their dwindling numerical advantage by launching a desperation attack on the Manticoran home system. The resulting battle results in over a million dead, and accomplishes nothing except to extend the war because the Manticorans are able to bring in reinforcements and outflank the attackers.
Later on, things deteriorate so badly between Manticore and the Solarian League (a power that, on paper, is much bigger and more powerful than Manticore and Haven combined), that the Manticorans sue for peace with the Havenites and declare war on the League. By this point, the Manticoran and Havenite governments have both realized that they were being played by the trueBig Bad, The Mesan Alignment.
In Footfall, this happens twice during an alien invasion. The first time, they nuke the territory the aliens took over (which was still populated by humans). The second, and significantly less significant time, they build and use a nuke-fueled spaceship. They did get most of the nearby area into bomb shelters before they took off, though.
In the Gaunt's Ghosts novel Traitor General, Feygor gets very badly sick and Curth has nothing left to help him. When Ezrah offers the use of a paste that contains normally highly-toxic - as in scratch a man with it and he dies - poison as a remedy like his tribe did, the team reluctantly decides to use it. It barely works.
One of the flashbacks in Ghostmaker has a group of Ghosts encounter a summoned daemon in one of the buildings they're clearing. With little hesitation and less time to flee, the Ghosts promptly request that one of the kilometres-long ships in orbit fire on the building.
In Isaac Asimov's The End of Eternity, there is a time traveling group that safeguards humanity over a period of billions of years. The problem is that humanity never leaves the Solar System, and after at least millions, maybe billions of years humanity dies out. The protagonist goes back to the twentieth century, and there manipulates the timeline so that time travel never arises, wiping out millions of years of human existence and destroying everyone and everything he ever knew.
In Neverwhere, the Marquis de Carabas can be called into one's service for the cost of "A really big favor". Take this warning in just case you should happen to find yourself in London Below: Don't do that.
In the Star Trek: Destiny trilogy, the Federation president gives Captain Picard permission to do anything necessary, regardless of Starfleet regulations or Federation law, to defeat a massive Borg invasion, up to and including re-creating Shinzon's thalaron weapon. Subverted in that Picard is ready to do this, until Geordi flatly refuses to carry out Picard's order to construct the device and proceeds to tear into him over it. Picard, shaken, then rescinds the order and finds another way.
LaForge: Repeat it as many times as you like, it won't make any difference. I will not resurrect that...that abomination. I won't be party to whatever atrocities it winds up being used for. When Shinzon had one, you were ready to die to stop it. Data gave his life to destroy it. For me to rebuild it now would be an insult to his memory and a betrayal of his sacrifice. I can't do that. I won't.
In Uhura's Song the Federation Council finds the plague sweeping across the Federation so serious that they suspend the Prime Directive and tell Kirk that they're trusting his judgement on how to get the cure that legends say exist on a planet he has only vague information about the location of. Spock misunderstands the reasoning and says they seem rather optimistic about their chances of finding the cure, despite his attempts to emphasize how flimsy their information is. Kirk explains that their apparent optimism is really grasping at straws because the situation is much worse than they (on the Enterprise) know. (It is strongly implied that the existence of the Federation and the survival of multiple member species is at stake. General Order One is not suspended lightly.)
In A Song of Ice and Fire, the arrival of the Others is considered this for people on both sides of the Wall. Mance Rayder, the King Beyond The Wall, is willing to march the Free Folk south of the Wall to find shelter in the despotic Seven Kingdoms. Jon Snow, for his part, is willing to allow "Wildlings" to settle on the Night Watch's lands and even join the Night Watch to bolster their ranks against the Others. Both plans are considered pretty shocking, and not everyone agrees with them.
In Timothy Zahn's The Conquerors Trilogy, the arrival of a dangerous alien threat starts everyone talking about dusting off a superweapon the humans used once and never used again. Subverted- the weapon doesn't actually exist, it was actually a freak accident where a solar flare wiped out a fleet.
Villainous example in the Dale Brown novel Sky Masters. His flotilla in shambles after a Filipino ambush, with only death or dishonourable retreat on the cards, Big Bad Admiral Yin decided to Nuke 'em. Things go downhill from there.
In The Hitchhiker's Guide to the Galaxy, when the Heart of Gold is about to be blown up, Arthur Dent decides at the last second that randomly activating the Infinite Improbability Drive can't possibly make things any worse.
Middle-Earth reached the Godzilla Threshold at the end of the First Age, as documented in The Silmarillion. Morgoth ruled over all of Beleriand and to defeat him the Valar unleashed a war that sunk all of Beleriand.
And again when Ar-Pharaz˘n sought to take Immortality from the Valar, the Valar unwilling to actively kill men, who as Children of Il˙vatar fall under their protection, instead give up their stewardship of the world and let God handle it, and the World is changed for it.
The Imass came to a racial consensus that after the latest in a long string of Jaghut Tyrants, the Threshold had been crossed. They transformed themselves into nigh-immortal undead and proceeded to hunt down every Jaghut they could, killing or binding them.
High King Kallor was so hated by a cabal of wizards that they chose to summon forth and bind a god to be used as a Fantastic Nuke against him. It destroyed an entire continent, created the Crippled God, and Kallor survived.
And in the course of the books, there can be so many gods drawn to a nexus of power that drawing in more hostile gods becomes a viable plan because they might start countering each other.
When the Polypond attacks the Great Ship in A Well of Stars, the crew decide it's preferable to burn away the entire fuel supply of the ship by firing up all of the ship's 14 world-sized fusion rockets, rather than allowing the enemy to rendezvous and take over the ship.
In the Animorphs prequel The Hork-Bajir Chronicles, the Andalite war-prince Alloran who eventually becomes Visser Three's host knew the Andalites had lost the war over the Hork-Bajir. Desperate to prevent the Yeerks from acquiring the Hork-Bajir, he unleashed a Quantum Virus, a horrific disease of space-time that breaks living beings down into molecules. He targeted the Hork-Bajir to deny the Yeerks their prize. All for naught, since the Yeerks had already captured enough Hork-Bajir to breed a sustainable population for their use. The Andalites covered up this horrific war crime to save face, and Alloran was left a bitter disgraced Shell-Shocked Veteran.
The protagonists in Larry Niven's The Ringworld Engineers are faced with the problem of Ringworld's increasingly unstable 'orbit'. The Ringworld has, or rather had, Ramscoops fixed around its circumference to act as station-keeping jets, using the solar wind as fuel. The Ringworld's inhabitants, presumably not knowing or not caring why the ramscoops were there, had 'borrowed' most of them to use on spaceships. The remainder could no longer keep the Ringworld centered on its star. There is a solution, but even the Pak Protector who discovers it is too horrified to enact it. They use the solar magnetic controls built into the Ringworld to temporarily increase solar wind output enough to provide the remaining ramscoops with enough fuel to re-center the ring. This has the unfortunate side effect of sterilizing a third or so of the Ringworld, killing trillions of humanoids via slow, agonizing radiation poisoning.
When things get really desperate in Stargate SG-1 and Stargate Atlantis, the higher-ups are usually willing to give the green light to plans that involve ridiculous things like blowing up suns.
One experiment of Rodney's kills a co-worker and blows up most of a solar system. They try it again. This time they almost destroy two galaxies, and completely drain their ZPM (an excessively rare and valuable super-battery).
The Replicators are so bad that every single one of their appearances has the line being crossed to further limits. Indeed Thor says that the reason the Asgard ask humans for help so often is that they lack the stupidity necessary to devise a plan that crosses that Godzilla Threshold. Said crossing involves such things as crashing ships into planets, using a one-of-a-kind state-of-the-art warship as bait for an explosion, and luring every Replicator in existence to the Asgard homeworld (and then collapsing the planet's star into a black hole, just to be thorough).
The Replicators have invaded the Milky Way, wiped out the System Lords and have begun attacking Earth. SG-1's final plan depends on an Ancient device designed to create (or destroy) all life, properly re-configuring it to only target the Replicators, and simultaneously firing it through every Stargate in the galaxy. And to do it, they have to team up with Ba'al, who was trying to reconquer the planet they were on at the time.
In the Season 6 finale, Anubis hovering with his finger on the trigger of an Ancient superweapon ready to blow up Abydos causes Daniel to break the non-interference rules of the Ascended beings and try to destroy Anubis using his godlike powers. He only fails because the other Ascended beings stop him.
In the The Ark Of Truth, one of the weapon systems the humans bring with them to the Ori home galaxy as a fallback in case their primary plan fails is a Replicator with reprogrammed failsafes. The failsafes turn out to not be as fail safe as hoped.
In a later arc of Atlantis, Rodney creates a reprogrammed humanoid Replicator to act as a delivery system for a computer virus to destroy the rest of the Asuran Replicators. Surprisingly, the standard tropes are subverted and the reprogrammed Replicator is perfectly content with her purpose in life as a "living bomb", delivering her payload without a hitch when finally deployed on the Replicator homeworld.
In the Doctor Who episode "Journey's End", there's Osterhagen keys; people who know about them start crying at the mere mention of their use. It's revealed that UNIT strung a series of nuclear warheads beneath the Earth's crust, with the stated aim of destroying the entire freakin' planet. It is only to be used when death is considered a preferable alternative to whatever shitstorm has enveloped the human race.
In a reference to Winston Churchill's real world invocation of this trope in defense of allying with Stalin (see below), he uses this same logic to justify using Dalek technology against the Nazis in "Victory of the Daleks." The Doctor tries and fails to convince Churchill that the Daleks are a bigger threat than the Nazis, but it turns out that the Daleks had out-gambitted the Doctor all along, and the entire point of the exercise was just to get the Doctor to admit that they were Daleks so that the Dalek race could be revived.
"Nightmare in Silver" shows that by the end of the "Cyber Wars", the Cybermen were such a threat it was worth obliterating an entire galaxy to finish them, with collateral damage numbering in the trillions. The protocol for encountering any survivors is to either terminate them or destroy the entire planet.
Several times in Supernatural, varied characters think they've hit this point:
By the end of season five, everything has gone so far to hell that risking giving Lucifer a total win by having Sam say 'yes' to Luciferis the only option. While this option guaranteed a fight between Michael and Lucifer that would destroy most of the world unless Sam could overcome the possessing influence of Lucifer long enough to throw them both into Lucifer's Cage, the apocalypse that would kill or zombify most of humanity would happen if they did nothing. Of course, at the end of season 4, they'd all pretty much realised that they were screwed.
Farscape: At the end of season 4 John does this with a home-made nuke in order to try to pull a fast one on the Scarrans and Peacekeepers. Done again on a much bigger scale in Peacekeeper Wars. John holds the entire galaxy to ransom with the wormhole weapon. This time, he really wasn't bluffing.
Also played with in season 3 when John finds out that playing with wormholes is fucking about with the entire fabric of reality. The only reason he reenters the system is that he has no choice. He still messes up though.
Angel: Series 4. The world is on the verge of an unexpected Apocalypse when the Beast blocks out the sun over LA to create a 24-hour demon playground. The only thing that can stop it is Angel's Superpowered Evil Side, Angelus, the greatest mass murder in recorded history and one of the worst vampires ever heard of. Even Angel agrees it has to be done and Angelus is freed. Then the only way to then stop Angelus is to break out the unhinged, convicted murderernote Said convicted murderer actually broke herself out, in a matter of seconds. as she was staying there by choice., Faith the Vampire Slayer, who has to use her Death Seeker nature to almost commit suicide because Angelus is that hard for even a slayer to defeat.
In The Sarah Jane Adventures episode "The Last Sontaran", despite the fact that Sarah Jane Doesn't Like Guns and distrusts the military, the presence of a Sontaran ship on Earth prompts her to immediately make plans to call in UNIT.
In the Star Trek universe, the Godzilla Threshold is instantly crossed whenever a single omega particle is detected. Omega protocol authorizes the captain of the vessel to use any means (even breaking the Prime Directive) to destroy it.
Kodos the Executioner/Anton Karidian in Star Trek episode, "The Conscience of the King" used this as his excuse to execute half the colonists of the Tarsus IV colony when a fungus destroyed most of their food supply.
It's worth noting that the only reason it counts as this trope was because he was wrong about one of his assumptions: It turned out that the Federation did manage to get relief supplies to the colony in time. Had he turned out to be right...
Deep Space Nine discusses this several times during the Dominion War arcs, both at a governmental level (with Section 31) and a personal and moral level (the episode "In The Pale Moonlight")
In the first season of Babylon 5, the station's dockworkers go on strike. Faced with a complete shutdown of the station's operations, Commander Sinclair is authorized to end the strike "By any means necessary". He does the unthinkable and reallocates part of the station's military budget to meet the dockworker's demands
Then, in Season 4, we see a real Godzilla Threshold crossed. First the Vorlons, then the Shadows decide to stop playing around and start laying waste to each other's allied planets all across the galaxy. They only solution they have left is to locate the rest of the First Ones, each Sufficiently Advanced Aliens on the level of the Vorlons and Shadows, and convince them to come back and engage the Vorlons and the Shadows in one last elaborate gambit.
In Twin Peaks, Agent Cooper uses some rather eccentric methods in the search for Laura Palmer's killer that have more to do with mysticism than forensics. Of course, he is not taken very seriously with these; at one point, Sheriff Truman demands that he lay aside these methods while the cops use traditional, realistic techniques in the search. But when Maddy Ferguson becomes BOB's latest victim, everyone begs him to use any remaining tricks in his bag in order to stop the killer once and for all.
Played for Laughs and Lampshaded Trope on Parks and Recreation. When Ron's first wife Tammi ("Tammi One") takes a hold of him again, Leslie tries to recruit his second, equally manipulative ex-wife Tammi ("Tammi Two"). Leslie explains 'When you are fighting Godzilla, you need Mothra.'
In Haven, Duke Crocker has the power to completely erase a Trouble by killing one person who has it. Duke never willingly uses it, since he finds killing abominable and Audrey and the others usually find a non-lethal solution to Troubles. Duke was willing to use it on a guy who's unknowing Reality Warper Trouble was about to destroy the town with an Alien Invasion he imagined, but Nathan then solves the problem before he can. Later, they face a guy who's organs progressively fail, forcing him to harvest organs from his family members, as well as trigger the same affliction in anybody who escapes from him. Audrey tells Duke he has no choice, he has to use his ability. Duke eventually relents and kills the guy.
The Toa's Novablasts from Bionicle. It's been attempted two times in the known story for such purposes — when Toa Jaller and the Toa Mahri faced all six of the Barraki and their army of sea beasts and tried to stop them from reaching Matoro (who was at the time busy resurrecting the entire fricken' universe); and when Toa Helryx tried to create a flood inside the resurrected but Makuta-possessed Great Spirit's brain, thereby causing the robot and the universe inside it to shut off, effectively killing every being in it — both attempts were hindered, thankfully.
In ice hockey, a team that is down a goal or two in the last minute or so may elect to pull their goalie and put another attacker on the ice. It gives the possibility of tying the game, at the risk of the leading team scoring again. On average, the leading team scores an empty net goal about 1/3 of the time while the trailing team scores a goal about 1/9 of the time - in the long run this strategy is detrimental to the team that pulled its goalie. However, in most cases what matters is that you've lost the game and not what the margin of defeat was.
Chaos. A cult uprising is one thing, but if daemons are actually rampaging around at will, the world may be past saving. Even if the Imperium managed to cleanse the planet, the taint of Chaos would remain, like lingering radiation that's also sentient and teaches people how to build dirty bombs. Of course, as Ciaphas Cain notes, the problem with destroying a planet in the grip of Chaos is that past a certain point the world isn't quite physically there anymore, so the best you can do is try to quarantine it.
Tyranids. If a Hive Fleet conquers a planet, even at a staggering cost, it will just add the world's bio-mass to the swarm and recycle the corpses of its dead, emerging only stronger. A controversial but effective tactic is to bait the Tyranids into committing most of a swarm to taking a world, only to blow it up before they can set about harvesting it, with any friendly casualties being acceptable losses. Unfortunately, the ever-evolving Tyranids have bred burrowing organisms capable of riding out such an orbital apocalypse.
In Space Marine, Exterminatus is on the table as a worst-case solution to an Ork invasion, not because losing a world to the greenskins is particularly dangerous, but because the world in question is capable of manufacturing Titans. The only reason the planet isn't glassed immediately is because those Titan-producing facilities are just as valuable to the Imperium as to the Orks, so the titular Super Soldier and his squadmates are sent in first.
In Dawn Of War II: Retribution the individual planets are not beyond saving, but the fact that not only all of the sub-sector has been under attack for the past ten years, but that they're being attacked by nearly every major threat in the Imperium means the region has devolved into such a clusterfuck that Exterminatus is seen by most in the Inquisition as the only viable course of action.
Codex: Grey Knights describes something called "the Terminus Decree." Knowledge of its existence is restricted to the Supreme Grand Master, who is only to access it when the fate of humanity's future is in peril.
As the Old World Of Darkness drew to a close, the Antediluvian vampire Zapathasura (sire of the Ravnos clan) rose in India and began wrecking things. The Technocracy responded with a Code Ragnarok, their contingency plan for 'if we don't win this, the world ends today' events. It involved solar mirrors (to direct the equivalent of five suns at the super-vampire), Prime-enhanced spirit-shredding nuclear weapons, weather control machines, and more. In fact, Ragnarok authorized the use of the entire Technocratic arsenal, a 100% civilian casualty rate and a 100% operative casualty rate — had Ravnos not been killed by the orbital solar mirrors, God only knows what they'd have used next. If they had anything else to use.
This being the World of Darkness, though, things did indeed get worse thanks to Code Ragnarok. The Shadowlands were destroyed, the Fallen escaped from the Abyss, and the Time of Judgement began. Though, to be fair, the other option was letting the world end that same day.
In Exalted, we have the Kukla. Elementals in Exalted take on increasingly draconic forms as they grow in power, culminating in a transformation into a Greater Elemental Dragon. The Kukla is a Greater Elemental Dragon of Earth, whose mere presence is so destructive that he's been sealed away until the Unconquered Sun, ruler of Heaven and arbiter of justice, decides that the situation in Creation is so far past the Godzilla Threshold that the general apocalypse resulting from the Kukla's release cannot possibly make things worse. Just to be perfectly clear: the Kukla is several miles long, utterly indestructible, completely insane, and possibly destined to destroy the world. Things have to be REALLY bad for "Release the Kukla!" to be a good idea.
Glories of the Most High revealed that the Unconquered Sun also has the authority to temporarily (if lucky) release a Yozi from Malfeas/Hell. Do mind that the Yozis are insane, world-making, world-sized Titans that have been seeping in divine amount of hatred and misery for several millennia. One of the Yozis, before being defeated by the Exalted, destroyed 90% of Creation — and the remaining portion is several times larger than Earth. Creation is liable to suffer several disasters where their presence is preferable to the alternative (and the Player Characters are tasked with taking care of it).
Beyond all of those is the Eschaton Key. When Malfeas created the Unconquered Sun, he granted him the power to utterly annihilate Creation in the event that any of its worst enemies should gain control over it. It's been used only once; to destroy the rival Creation that an enemy Primordial attempted to supplant the original with. After that, the Unconquered Sun sealed his world destroying power within a broken device that is beyond the ability of anyone less than the most powerful Solars to repair and operate.
Return of the Scarlet Empress revealed that if things get really, really, Ebon-Dragon-just-signed-his-name-on-the-Moon bad, there are certain world-shaking Astrology charms that can be unlocked for the Sidereals. These allow them to do things like give gods or Exalts battlefield promotions - to Celestial Incarnae.
Any situation in which you would consider casting Vengeful Gaze of God in D&D 3rd Ed is probably past the Godzilla Threshold. For those who don't know, it's an epic level spell that will almost certainly kill whatever you're casting it on...but the chances of the caster surviving too is slim to none. Even the book says, "The backlash damagenote which is in the hundreds of dice will almost certainly kill the caster, but most would consider this cost worth it."
Or, in 3e/3.5e, anything in the Elder Evils rulebook. By the end of the plot arc involving (insert featured superboss here), a spell that obliterates your section of the Multiverse would probably be deemed an acceptable course of action to stop those creatures, especially in Atropus's case.
3.5e's Wu Jen spell, Transcend Mortality. When you cast the spell, you become nigh indestructible for the duration. The cost? You burn out the rest of your life force to cast the spell, and when the effect ends, turn into a small pile of ash.
It is generally known that if someone tries to put one extradimensional storage device (e.g., a Bag of Holding) inside another (e.g., a Portable Hole), the result is a catastrophic rending of the fabric of the universe. The extent of this rip depends on the GM's whim, but by and large the result is usually miles in diameter, cannot be done from range, and kills everyone and everything within the "blast" zone. (Okay, there's a slim chance of being cast into another plane instead.) Adventurers have been known to do this anyway, if the situation is dire enough.
The artifact called the Bringer of Doom opens a massive cross-rip into Hades and releases thousands of hordlings over a radius of several miles. The user never survives.
A mage with a staff of power or staff of the Magi can perform what is euphemistically called a "retributive strike" — breaking the staff itself, killing herself and making a very big mess of the surrounding area.
Players in Call Of Cthulhu with a bent towards magic can summon Azathoth to Earth. Azathoth, FYI, is the boss of bosses of the Lovecraft Mythos, the blind idiot god that sits at the center of reality and is best described as a cross between an titanic amoeba and an ever-expanding nuclear explosion. Presumably, a sane player would only do this if the stars have become so right that Cthulhu and his pals are tap-dancing down Main Street.
Keeping the mechanics of the game in mind, any situation where summoning Azathoth wouldn't make the situation significantly worse will almost certainly already have rendered all the player characters irretrievably insane.
In Duel Terminal, the background fluff behind the Hidden Arsenal series of Yu-Gi-Oh!cards, the Ice Barrier tribe fought against the invading Worms and Fabled by progressively unlocking seals on a series of powerful Ice Barrier monsters. Eventually, they wound up pushed so far back against the wall that they released Trishula, Dragon of the Ice Barriernote a Game Breaker in Real Life. In its berserk rampage, Trishula wiped out nearly everybody, friend and foe alike, including the Ice Barrier tribe themselves. Later expansions on the storyline imply that there were survivors, just not very many.
In Witchcraft the Mad Gods are seen this way by the Mocker covenant (and doubtless other factions). The point is made that if an incarnation of a Mad God is imminent, a Mocker will stop at nothing to prevent it ("If doing so requires him to detonate a nuclear device in downtown New York, so be it").
Trinity almost had this as part of the backstory. When the Aberrants were truly ruining the world, China politely informed them that if they didn't leave the planet immediately, the entirety of China's orbital platforms would perform a simultaneous nuclear bombardment on every surface of the earth until it was turned into glass. Rather than preside over an empire of smoldering, irradiated, fused carbon and silicon, the Aberrants decided to take off, and China took its proverbial finger away from the Big Red Button.
One high-clearance Paranoia NPC, faced with the prospect of another one blowing up all of Alpha Complex with an Old Reckoning antimatter bomb, gives the PCs his ID card before running away from the approaching interrogators.
In Super Godzilla, this actually happens several times: The first, when the Japanese government decides to awaken and control Godzilla in order to fight aliens and the monsters they send (making this one a literal example of the Godzilla Threshold); later, when making Godzilla stronger by way of injecting King Ghidorah cells; and in the final two stages, where it becomes necessary to pour huge amounts of energy into Big G in order to turn him into the titular Super Godzilla.
In the Geneforge series, the rebellion which breaks out in the 3rd game is on the edge of defeat by the 4th. While the humans and serviles in the rebellion could survive being ruled by the Shapers again, the drakons know they will not be allowed to exist under Shaper rule. To turn the war, they create the Unbound, which are massively powerful but completely insane, and release them into Shaper lands to rampage around.
In Halo 3, when a flood infected ship crashes in New Mombasa, Commander Keys proposes to overload a slipstream engine inside the city and wiping out everything in the area. Though usually rather timid in his decisions, Lord Hood only replies with "Do it!".
The Flood evoke this reaction in more than just humans: again in Halo 3, when there's a relatively small Flood outbreak in Africa, the Elites who show up in a Big Damn Heroes moment torch the continent to get rid of it. When Lord Hood protests this action, the Elite Shipmaster responds that he fully intended to burn all of Earth just to make sure that every last Flood spore was absolutely dead, and only the Arbiter's arguing against it stopped him from doing so.
The Halos themselves were built (and activated) due to the Threshold being crossed: wiping out all intelligent life in the galaxy was an acceptable alternative compared to the Flood, as far as the Forerunners were concerned.
In Halo Reach Kat comes up with an insane plan after the Covenant super-carrier arrives at Reach, to which Cater replies he'll ask, but they'll never get a green light for it. One Gilligan Cut later...
It's a relatively minor and easy to miss one, but in AC4: For Answer you can become one, if you kill hundreds of millions of people by bringing down the cradle, Otsdarva will be one of the 5 NEXT teaming up to take you down as payback.
In Dirge Of Cerberus, Omega WEAPON's function is a Godzilla Threshold to the previous one. If destroying the threat with the other WEAPONs doesn't work, it packs up all the Lifestream it can and heads off into space to find another planet to colonize.
World in Conflict:Nuking Cascade Falls to prevent the Soviets from finding about SDI (the only thing stopping the Soviets from using nuclear weapons...and a fake reassurance, since it's completely non-functional), and at the end of the game, nearly nuking Seattle to prevent the Chinese, coming to reinforce the failing Soviet invasion, from landing there.
In Mario & Luigi: Bowser's Inside Story, Bowser can only be turned into Giant Bowser when his life is in mortal danger, e.g. when he is flattened by an enemy far too big to fight normally. Almost a literal case.
At one point in Tales Of The Abyss, Jade suggest that the only way to save the world is to sacrifice the lives of 10,000 replicas, which in game basically boils down to sacrificing 10,000 babies. A few hours later you really don't get a choice otherwise.
Villainous example occurs in Star Fox 64. Facing down a battalion of Andross's ships, the general is throwing everything on hand at you, save for a prototype the scientists insist is too dangerous. At the end of the level, he yells "Deploy it now!" and the prototype serves as the boss - a biomechanical dimension hopping battlecruiser with free will.
The second disk of Wild Arms 2 reveals that pretty much every threat from the first disk, from the terrorist organization trying to conquer the world to the Eldritch Abomination sealed inside the protagonist, was part of a plan by Irving to combat the most ludicrously overpowered threat of all time: a parallel universe that eats other universes.
In Shin Megami Tensei: Devil Survivor, the government has a 'final option' that it will unleash on the Yamamote Line if they can't take control of the situation taking place inside, and is why nobody inside has more than six days to live. It's a chip installed in all japanese electronics that lets the government control them remotely, and use it to create enormous amounts of EM radiation which would fry every electric circuit and every living being inside. Incidentally, this is the smallest of three Thresholds in the game.
In Devil Survivor 2, on Friday, you discover a giant magic circle. Later that day, you encounter the Asteroids Monster Mizar. Attacking one of its blobs with anything short of a One-Hit Kill causes it to split, and leaving them alone allows them to grow and split at their leisure. At the rate it's growing, Mizar will be everywhere in a day. When you mention the magic circle to Yamato, he reveals that its power would suffice, but it's currently preventing the last few steps of The End of the World as We Know It. He forces you to work it out yourself, but it does turn out that Mizar is now the bigger threat to existence.
Starcraft, the Protoss consider the Godzilla Treshold crossed when they find out the Zerg have infested a world. Their standard solution is an orbital bombardment that burns everything on the planet to a crisp.
Arcturus Mengsk sees the Confederacy's corruption as having crossed the threshold to justify using a psi emitter to lure the Zerg to their capital world, then lets the Protoss burn the Zerg and Confederates both. However, its only Mengsk who sees it this way, the others see it as a Moral Event Horizon for him.
Then along comes StarCraft II, when it turns out that the Zerg need to be allied with against an oncoming threat even more terrible — a fallen Xel'Naga, and an army of even more lethal Protoss/Zerg Hybrids.
In World Of Warcraft, the Godzilla Threshold is pretty consistent: for really, really bad threats, the Horde and Alliance work together. Most of the time they're at each others' throats in a Cold War or even proxy war. Against pests or regional threats, the Alliance and the Horde ignore each other or even try to backstab each other so their own people can claim the prize first. But against an awakened Old God, the beachead of a demonic invasion, the Lich King, or the biggest and most evil dragon ever, they ally. Temporarily.
Unfortunately, with the rising tensions between the Horde and the Alliance, the level of threat required for them to put aside their differences becomes even greater. Ultimately, however, Garrosh himself is in the process of becoming the common threat that requires the Alliance and Horde's combined efforts to defeat.
The Enclave in the Fallout series sees the proliferation of mutants in the wasteland as their threshold. Unfortunately for everyone, to the Enclave "mutant" doesn't just mean the super mutants and deformed ghouls, it includes any human who has been exposed to radiation for an extended period of time, in other words everyone not a member of the Enclave or living in a Vault. Their solution is to use a modified strand of the FEV virus and release it into the air currents and later water supply to kill them all.
Capcom loves this trope, from the total destructions of Raccoon City in Resident Evil 3 Nemesis and Fortune City to the massacres at Santa Cabeza and Willamette in Dead Rising.
In Dragon Age: Origins, the Templars believe the threshold has been crossed after the Circle Tower is overrun by abominations. Their Knight Commander has already sent word to the Chantry in Denerim requesting permission to invoke the Rite of Annulment which would allow him to use the full might of the Templars to completely purge the Tower. This happens at the worst possible time since you really need the support of the mages against the Blight. You do have a couple options though: 1) kill the abominations yourself and save the mages, or 2) kill everything in the Tower and have the Templars now free of their responsibilities of mage babysitting join you.
The Blight has played this role for over a millenium, to the point where the Chantry is willing to look the other way when the Grey Wardens recruits criminams, apostates, or decide to dabble in blood magic.
The games show actually several cases where the Wardens habit of breaking Chantry's laws with impunity backfire, like the mess left by Sophia Dryden's rebellion, or what happened with Corypheus' prison or, the most obvious case The Warden Commander of Ferelden taking Anders under his/her wing
Some mages fighting for their freedom or life decide to use Blood Magic or make deal with a demon. These situations usually end up badly - with the unfortunate mage getting possessed or driven insane with power. There are also shades of Then Let Me Be Evil, since many mages believe that if templars are going accuse them of Blood Magic anyway, they can as well go along with it and use the best weapon they have on their disposal.
Upon discovering what lay beyond the adamantine the hard way, Bay 12 forumgoer SpiralDimentia decided to release his captive (hostile) bronze colossus in hopes of it fighting the... you know. This didn't work, but was applauded as sufficiently dwarven, especially since he tried to resettle the place twice after losing everything, despite the bronze colossus and the... you know... still being in residence there.
Failed miserably in one fortress that was being attacked by husks, and decided to Breach the Circus; it turns out that DEMONS are insufficiently Godzillaesque to defeat husks.
In Modern Warfare 2, Captain Price's plan to fire a Russian nuclear missile at the US Eastern Seaboard in order to use the EMP to stop the Russian invasion:
Price: Do you know how to put out an oil fire, sir? You set off a bigger explosion next to it. Sucks out all the oxygen. Snuffs the flame. (...) We've got a pretty big fire. We're going to need a huge bang...
Also in the sequel, when the team has to take Makarov's bomber, Volk, out of Paris alive so he can be interrogated. When they get to the bridge over the Seine, they meet a Russian barricade which won't let them through. The air support manages to wipe them out, but in the process they end up bringing the Eiffel Tower down. This is because the President gave them a clear order to do what they have to do to bring Volk alive.
In BlazBlue, Litchi crossed this in two phases on a personal case. The first phase, on realizing that Lotte Carmine was inflicted with an extreme corruption of the Boundary which practically has no normal permanent cure and begging for Kokonoe to help does no use, she sees it fit to corrupt herself with the Boundary to find symptoms and develop the cure from experience. The second phase is when she found no cure overall and her own corruption was getting to her, she sees it fit to join the NOL for the small hope of cure, despite the organization storing someone who's pegged as extremely shady and suspicious (Hazama), or blatant monster of a father (Relius).
In Mortal Kombat 9, after an effort to change timeline causes Sindel to brutally murder the majority of the heroes, Raiden sees it fit that the only option left is to ally with Quan Chi to stand a chance against Shao Kahn, with the souls of the dead heroes as the wager. The bad news, Shao Kahn already sold the soul of the heroes to Quan Chi. The good news, only by fighting the dead heroes would Raiden get an Eureka Moment on how exactly to beat Shao Kahn.
In the Mass Effect 2 DLC Arrival, this is invoked, as the Reapers are set to arrive at the Alpha Relay in mere hours. There is only one viable solution to stop it from happening: destroying the Relay, and thus setting off a supernova-level explosion that wipes out a nearby colony world with 300,000 batarians. It isn't pretty, but it has to be done.
Due to Shepard's actions in "The Arrival", they have been branded a War Criminal and Terrorist throughout Citadel Space. Then the Reapers arrive. The charges are immediately dropped because not only does everyone realise that Shepard was right, but they are the only person who's ever been capable of actually killing them!
The continuity's equivalent of Godzilla, the literal mother of all Thresher Maws, is summoned and it proceeds to eat a Reaper.
By the end of the game, your coalition can include several of the biggest threats in galactic history.
Admiral Hackett points out that there is no way in hell that a super weapon as powerful as the Crucible would ever be seriously considered under normal circumstances, but the Reapers have forced humanity's hand. Indeed, no one even knows what the Crucible even does, all they know is that it can generate an immense amount of energy. The fact remains that the Crucible is the only thing in the galaxy with enough raw power output to defeat the Reapers, though, so...
The Codex entry "Desperate Measures" discusses different ways that are being considered to stop the Reapers that would never be considered in normal warfare, such as destroying mass relays to strand them in distant systems (they'd just go the long way) or ramming them with starships traveling at FTL speeds (integral safety protocols make it impractical at best).
One planet decided to blow itself up so they didn't suffer a Fate Worse Than Death and become indoctrinated.
All three possible endings of the game involve this in one way or another.
Has happened at least once in Touhou. At some point in recent history, humankind's disbelief of anything supernatural had grown enough to threaten the very existence of supernatural beings. Seeing this situation, the youkai sages decided to erect the Hakurei barrier to rip Gensokyo from real world, so that the land become the final haven of everything supernatural. They knew that they were going to offend the Dragon of Gensokyo, and the Dragon did appear in all its catastrophic glory, covering the sky from one horizon to the opposite, while downpouring from the Dragon's body threatened to drown the land. Amazingly, the Dragon was willing to listen to the sages, and it agreed to their plan. Then it disappeared, and (thankfully) never seen again since then.
A possible result in The Elder Scrolls V Skyrim. Your character may be the leader of the Thieves' Guild, the Dark Brotherhood, have completed each Daedric quest (even the ones that involve murder, betrayal, torture, and cannibalism), and murdered hundreds of innocent people. But the Graybeards will still teach your character the way of the Voice, despite being someone that will doubtlessly abuse this power, because you're still the world's only hope at defeating the dragons.
In Saints Row The Third in one possible ending, after a beloved monument is destroyed, Senator Monica Hughes allows STAG to deploy the much hinted-at Daedalus, an Airborne Aircraft Carrier that begins indiscriminately attacking Steelport in a desperate effort to wipe out the Saints.
Pops up in the final GDI mission of Command And Conquer 3: Tiberium Wars. Faced with a grueling assault on an enemy stronghold in hopes of ending an Alien Invasion, Director Boyle will urge you to use the Liquid Tiberium bomb to wipe out the foe with a single press of a button - even though doing so will set off a chain reaction in the world's largest Red Zone, killing millions if not billions of civilians, causing irreparable environmental damage, and annihilating your own army. However, as hard as the fight is, your forces are still capable of winning without using the bomb and thereby destroying southern Europe.
Gears of War: In the backstory, the Locust invasion was so devastating that the Hammer of Dawn Kill Sat was used to destroy all the major cities to slow the advance. In 3, you deal with the aftermath of this when you visit Char, a city that was leveled by the attack.
Apparently Professor Gerald using an alien's DNA to create the Ultimate Lifeform was the Godzilla Threshold for G.U.N. to storm Space Colony Ark and arrest (or kill) everyone on-board.
In Dark Souls the Darkwraiths sealed under the flooded city of New Londo caused a Godzilla Threshold. The Darkwraiths you see are corrupted, evil monsters who devoured humanity (The precious, ethereal substance, not actual people). There were such a threat to anything that possessed a soul that the Sealers, a group of pacifists, flooded an entire city, drowning its entire populace just to seal them away.
The fading of the First Flame is the threshold for the gods. The Fire is so sacred, that they are willing to do anything to keep it burning just a little while longer. The Witch of Izalith attempted to use her Lord Soul as a replacement. When that went horribly wrong, Gwyn divided his Lord Soul up and plunged into the First Flame himself to reignite it. He's been burning alive in it ever since. And now that it's fading again, what remains of the pantheon is ready to sacrifice one hapless Undead and the remaining scraps of the Lord Souls to keep the Flame lit.
Blast Corps has a truck with a pair of defective nuclear missiles. The truck's computer goes on the fritz and winds up locking the controls while going on auto-pilot mode and goes directly straight to its destination, regardless on what is its way. The slightest jolt will cause the missiles to explode and destroy everything in a several mile wide radius. The solution? Destroy entire towns and cities by using machines and vehicles designed for destruction so that the truck has a clear path. The game even keeps track on how much damage you caused, which can easily skyrocket to the millions and billions of dollars. You will level entire towns, but it's a small price to pay to avoid a nuclear winter.
In Dragon Age II, during the Qunari invasion of the Kirkwall, the situation gets so dire that when Knight-Commander Meredith discovers that Mage!Hawke has been operating as an illegal apostate under the Templars very noses for the last four years... she does the smart thing and immediately declares a truce until the crisis is dealt with! At this point, she needs all the help she can get in retaking the city, even if it comes from an Apostate Mage!
In Knights of the Old Republic, the backstory of the Jedi Exile is that they confronted this at Malachor V. The situation became so dire they were forced to unleash a superweapon, which ended up not only killing every single thing on the planet, but the entire fleet in orbit! The sheer scale of the destruction caused the Exile to become severed from the Force and lead them to willingly accept exile on the Outer Rim for over ten years.
In the Super Robot Wars Original Generation, there's two Godzilla Thresholds. The first is the usage of Only One Crash and the creation of the Super Robot SRX and the powerful Hyper Tromium Buster Cannon. The second? Unsealing the RTX-008L Huckebein L, one of two robots powered by a black hole and basically weaponizes it.
Briefly considered in Assassins Creed III. In one conversation with Rebecca, she suggests presenting all of the information the team has gathered to Abstergo so they can help avert the solar flare. Desmond replies that he actually considered that option, and only refrained from doing so because he believes Abstergo already knows about the threat and is trying to take advantage of it. The very idea of Assassins seriously considering working with Templars, in particular Desmond who has been imprisoned and experimented on by them, shows just how dire the situation is. Later, Minerva will actually encourage Desmond to allow the solar flare to wipe out most of humanity rather than set Juno loose. Juno is apparently that dangerous.
In Shin Super Robot Wars, Ryouma Nagare, for his part, is rather reluctant to invoke the potentially catastrophic might of the Shin Getter, but will admit the aliens pose an even greater threat.
In Batman Mask Of The Phantasm, Salvatore Valestra tries to hire the Joker to take out Batman, under the belief that Batman is knocking off people connected to Beaumont (it's someone else), and hopes that since Joker is one of these people he will take the job. He laments having been pushed to the point where it's necessary, and Joker kills him to bait the real killer.
Same thing happens in Batman Under The Red Hood when Black Mask breaks Joker out of Arkham in order to deal with the Red Hood. What he didn't know was that this was exactly what Red Hood wanted.
One episode of Justice League Unlimited had the heroes use the Kill Sat integrated into their orbital base when facing a geometrically reproducing Grey Goo swarm of replicating robots. They were called on it by the government (especially as they had kept it a secret), and this later spawned a great deal of mistrust and a hijacking of said Kill Sat.
When Darkseid shows up, Superman fights him without restraint while giving the trope-naming "World of Cardboard" Speech. The damage to the city is immense. He is also the only villain that Superman is perfectly willing (and actually WANTS) to kill.
And just before that, the Legion of Doom crosses their own threshold in response to Darkseid: they go to the Justice League for help.
In general, the League has "Omega" level threats, that require every single League member to drop everything and fight. We've only seen four such cases in Unlimited, two being the already mentioned Grey Goo and Darkseid invasion, while a third was against an extremely powerful magician, and the last was when the android Amazo returned.
Amazo had basically achieved Godhood at that point, and appeared to have destroyed the planet of the Green Lanterns on it's way to Earth. Even the Martian Manhunter thought that the only option left was to let the Green Lanterns use all their remaining power to destroy the Android, which would of taken about Half the Earth with it.
In another universe, Lex Luther had become president, killed the Flash , and was about to cause some kind of mass war (most likely nuclear) that could destroy the planet. This is what pushed Superman past his no killing code, and made the Justice League take control of the Earth.
The DuckTales episode "The Uncrashable Hindentanic" revolves around Uncle Scrooge and his new airship. His sidekick and perennial crasher of aircraft Launchpad desperatly wants to fly it but is told that Scrooge actually wants to keep the airship in one piece. When the events of the episode conspire against this Scrooge eventually relents and tells Lauchpad to take the wheel. They crash, but Launchpad accidentally takes out the opposition while saving the passengers.
"If we are going to crash anyway, we may as well crash with style."
In one of The Simpsons Halloween episodes, giant advertisements are taking over the town. The solution: just don't look. A ridiculous solution, but as nothing else has worked, everyone does so without hesitation (except Homer, being tempted by Lard Lad's giant donut; Marge eventually pulls him away).
In the Danny Phantom episode "The Ultimate Enemy" Clockwork actually alters time—consider that he is in charge of maintaining the proper flow of time—to stop Dark Danny from coming into existence.
In the last few minutes of the Ben 10 Ultimate Alien episode "Forge of Creation", Aggregor defeats the heroes and is moments away from acquiring Reality Warper abilities that will grant him eternal power over the universe. Kevin then absorbs energy from the Ultimatrix to go One-Winged Angel to stop him, knowing that this will make him insanely evil again. Thankfully, Ben's younger self is able to guilt-trip Kevin out of trying to steal the Reality Warper powers for himself.
In Teen Titans in the episode "Aftershock" pt. II, Terra realizes that the only way to stop Slade, after he took control of her body with a suit that fused into her very nerves and used her body and powers to beat up the Teen Titans and she had unleashed a volcano that could destroy the entire city, she realizes she is the only one who has any chance of stopping the volcano. So she kills two birds with one stone, stops the volcano and kills Slade with the lava, and is fossillised in lava and becomes stone.
Some of the situations in Megas XLR are across the line, such as Earth being invaded by the almost unkillable metal-devouring robot R.E.G.I.S. Mk 5, which had been scheduled to be thrown into a black hole until Coop accidentally rammed the ship transporting it. The only problem is that Coop is nowhere near smart enough to identify which situations are across the line, and as a result tends to Godzilla every problem whether it's appropriate or not...and, of course, most of them are his fault anyway.
For the record, he discovered that the R.E.G.I.S. Mk 5 was solar powered and would forever stay active so long as there was light to power it. Coop's solution was to block out all sunlight so it couldn't operate. He does this by creating a nuclear winter scenario by belching enough smog out of his engine to block out the whole damn sky.
In Hot Wheels Battle Force 5, Sage was forced to freeze the entire Red Sentient race to stop her Evil Twin brother Krytus from leading them on a multiversal conquest. When Krytus and her have their final confrontation, she tells him she did it because he was a threat to not only her entire race but the multiverse and she had to. Krytus' response? "You were right!" It says a lot when the guy she used it on is well aware that she was justifed for doing so and doesn't care.
In the second season of Re Boot, a web creature evades capture and deletion to open a massive invasion portal from the web. This jolts the entire Mainframe system into survival at all costs protocols, Phong uniting with both Megabyte and Hexadecimal to build a portal closing supercannon and building a massive common army to hold the invaders at bay long enough to use it.
South Park, "It's a Jersey Thing": When over half of America is taken over by New Jersey, the nation eventually turns to Al Qaeda for help.
Johnny Test: In the episode "JX5: The Final Ending" Johnny, while in an Enemy Mine situation with five of his archenemies who have gained his powers, suggest that they form one huge Power Poot to destroy Dark Vegan's flagship after he rips out the self-destruct button. It works, destroying the entire fleet.
In "Johnny X Strikes Back...Again!" the CIA's two Gone Horribly Wrong supersoldiers actually succeed in taking over the world, and they're arguably the most powerful villains on the show, so Johnny copies his powers to at least ten other characters to destroy them.
In the final episode of WITCH, the Guardians are forced to use the Zenith forms, basically becoming their trademark elements, to battle a massively powered up Cedric. It nearly goes sour as the girls lose themselves in this form.
Homestuck: By Act 5, all the kids' plans to deal with how screwed up their Sburb session has gotten fall into this trope. Then things get so bad that they execute all three plans at once.
Floyd had this exchange when our heroes were scheduled to stew for giants:
Carmen: Now... Floyd, it's time for you to learn a spell that may get you out of this mess.
Floyd: Um, Carmen? You said that me casting spells was a bad idea!
Carmen: It is, but you two being eaten is marginally worse.
What the SCP Foundation are prepared to do to contain some items. Then again, an awful lot of the things they deal with really are that dangerous. Most foundation sites must have a several megaton strong nuke armed at all times for exactly this kind of situation.
Their opposite-number the Global Occult Coalition has Emergency Procedure "Pizzicato" for massive emergence of Threat Entities. Force authorisation states that "All restrictions re: NBC weaponry, Memetic Cascade Sequences, and Nanotech Grey Goo items withdrawn" and "Acceptable Collateral Damage: 90% of worldwide human population".
Quantum from the Global Guardians PBEM Universe was the most powerful superbeing on Earth. He was quite literally capable of disintegrating the moon, had he wanted to, but of course he never wanted to. When the Xorn invaded, he went out to meet their attack fleet in space and finally let himself cut loose. It was almost enough.
The Director of Red vs. Bluecreates Godzillas just so he can be ready for this:
Director: When faced with extinction, every alternative is preferable!
Pretty much every plan to deal with Tennyo in the Whateley Universe. One we saw in a holographic simulation destroyed the Eastern Seaboard of the U.S. and plunged the planet into nuclear winter. And they considered it a reasonable alternative.
They also have Plans A-Z...
In Worm, the Endbringers are three Nigh Invulnerable, superpowered monsters who have collectively brought humanity to its knees over the course of decades of city-destroying and superhero-slaying attacks. Nuclear weaponry, orbital railguns, advanced tricks with teleportation...all have been brought out against them, and it never worked. Most recently, Phir Sē, an Indian parahuman with a Portal Network, brought out an attack that could potentially not only kill the entire city of New Delhi, but also the superheroes defending the city against the Endbringer-heroes who have been the only ones to hold them back in all their history.
Quite a few medical treatments, both current and historical:
Both chemotherapy and radiation treatment are poisonous and can cause significant side effects - elevated risk of secondary cancers, bone marrow destruction, hearing loss, brain damage. But when the alternative is death from cancer, and especially when there's a reasonable chance of curing it with the chemotherapy...
Thalidomide, originally developed as a sedative and anti-nausea drug, causes horrific if not deadly birth defects in infants and has been generally banned by most countries since the 1960s. However, it has been shown to be effective at treating serious conditions like drug-resistent leprosy. When prescribed to fertile women for a serious enough condition, the patient uses multiple contraceptive devices and is carefully monitored.
In the modern era, syphilis may not seem like a terribly frightening disease. Yet it was the HIV of its era, potentially causing a dementia-like condition if left untreated. One of the only somewhat effective treatment was mercury injections, which certainly caused significant side effects but were preferable to tertiary syphilis.
Overprescription has led to the Godzilla Threshold being lowered (sometimes a bad idea in many cases) but before overprescription, the only way one could get an antipsychotic (what used to be called the major tranquilizers) was to be frankly, overtly schizophrenic or manic and in an episode with complete loss of touch with reality, and before overprescription for stimulants, someone had to be so unfocused that no coping strategy worked and they were practically bouncing up and down the walls.
This does exist for drugs if they are specifically known as drugs of abuse. In extreme cases, sometimes requiring being enrolled in a trial, one could be prescribed: ecstasy for PTSD and major treatment-resistant depression, opiates for treatment-resistant depression, psilocybin for intense migraine or cluster headaches. The condition has to be so severe that all other medication approaches (everything from antidepressants to antipsychotics to anticonvulsants to every possible cocktail of them) and doses and all non-medication approaches (everything from cognitive behavioral therapy to electroshock) have either failed, are failing, or bear too much risk for the patient and the addiction that will result from opiates or the potentially fatal side effects of a dose of ecstasy are better outcomes than suicide or disability so severe the individual is literally bedridden or suicidal.
Yet another example here would be the "ibogaine cure" for alcoholism or drug addiction where nothing else has worked. Ibogaine itself is toxic (more so than psilocybin or LSD which have had similar effects) but legal in some areas, it is unique for producing scary and bad "trips" but at the same time, often triggering something in the brain that reboots the mechanism of addiction, if the process is managed correctly (and if it is managed incorrectly, death may result).
Treating addictions with a substitute addiction or substitute substance also falls under this. A lot of people would be the first to agree that being an addict to anything isn't good, but moving someone to one that is less damaging to their health from one that is objectively worse is sometimes the only workable option. For example, getting The Alcoholic to become The Stoner or even a junkie might seem absolutely counterintuitive and unethical - but if said alcoholic is developing liver disease, cannabis is far less hepatotoxic than alcohol, or if they are developing chronic alcoholic encephalopathy, cannabis or even opiates are far less permanently damaging to an adult brain than alcohol. A similar variant of substitution can actually be seen with the prevalence of coffee and soda and cigarettes in many recovering addict spaces.
The Milwaukee Protocol is an experimental treatment for rabies, once symptoms appear in an unvaccinated individual. Given that rabies is invariably fatal within only a few days of the onset of symptoms, putting the patient into a coma and shooting them up with a myriad of drugs can literally do no more harm. And even then, the survival rate stands at 4 out of 35 treatments performed to date.
An individual example. 6 year old Emma Whitehead was terminal with Leukemia, so the doctors attempted the most radical treatment available: Injecting her with genetically modified HIV.
The very concept of Mutual Assured Destruction is a (so far successful) attempt at averting the trope, proposing that no-one could win any large scale use of nuclear weapons and that there is no possible way the Threshold could actually be reached.
A truer crossing of the threshold was Operation Downfall - if the Japanese hadn't surrendered, then the Allies would have launched the largest amphibious/naval operation in history: Hundreds of capital ships, thousands of aircraft, millions of men, chemical weapons, and, most chillingly of all seven atom bombs. The estimated casualties for the conquest of Japan was 1.7-4 million for the Americans and 10 million for the Japanese.
Inverted during the development of the atomic bomb: Physicist Edward Teller informed Robert Oppenheimer that there was a chance that detonating an atomic bomb could ignite Earth's atmosphere. Oppenheimer insisted that the figures be re-checked, and if there was a greater than 3 in 1 million chance of that happening, the project would not go ahead. Quoth Oppenheimer, "Better to accept the slavery of the Nazis than run the risk of drawing the final curtain on mankind."
World War One: The German Reich, being an authoritarian, militarist Monarchy, hated and feared Communism with a fiery passion. But when the Western Front bogged down for several years, they smuggled Vladimir Lenin into Russia, hoping he'd screw that country up even further and force it out of the war. It worked, leading to the Treaty of Brest-Litovsk, whereby Germany got huge swathes of territory ceded to them by Russia in exchange for peace, and the entire Eastern Front army could be transferred to the Western Front for the Spring 1918 offensives. Of course, the cost was the creation of the USSR and the rise of Josef Stalin, which led to...
The Midwives of the Birth of Nazism. Fearing the Dirty Communists of Josef Stalin's USSR, many in the West looked favorably on the rise of Adolf Hitler and Those Wacky Nazis, because their blatantly anti-Communist rhetoric made them seem like a good buffer zone between the Soviets and the West. Further, many in the West thought Nazi Germany was spiffy: to some, after the Ribbentrop-Molotov pact, Nazi Germany was a Socialist power allied to the Mother Revolution in Soviet Russia. Others thought Nazism was the One-Winged Angel form of Capitalism and were delighted to "see the death throes." Still others thought any Socialist revolution was better than Capitalism/classical liberalism.
Of course, this trope was also played even straighter in the USSR, as paradoxically the Soviets saw a rearmed Germany as a valuable buffer between themselves and the West dating back to Seeckt's proposals for joint defense, and the USSR played a leading role in recreating the German military. Even after Hitler rose to power, he and Stalin hashed out several agreements designed to expand to their mutual benefit at the expense of Eastern Europe's independent states. This, of course, led immediately and directly to...
World War II: Winston Churchill was one of those rabidly anti-Communist leaders in the West, but he also realized that the Nazis were worse. So, when Hitler backstabbed Stalin and invaded Russia in 1941, Churchill went back on a lifetime of opposing Communism by immediately offering alliance and aid to the Soviets. When questioned on the wisdom of this by his political allies, Churchill famously stated that "If Hitler invaded Hell, I'd find something favorable to say about Satan himself." Of course, allying with Stalin did work as far as defeating Hitler went, but that in turn led directly to...
The Cold War. Western nations often couldn't think of anything worse than seeing another nation fall to Communism, so if keeping the Dirty Communists out meant backing ruthless right-wing military dictatorships in third world nations, so be it. The Commies for their part didn't have any problems with working with ruthless left-wing dictators to keep American Puppets out of power in various nations. Of course, even by those calculations, sometimes, the Godzilla Threshold wasn't quite met to the extent that going nuclear was worth it, which is why we didn't end up fighting nuclear war over Vietnam, Korea, Cuba, Angola, or any of a dozen other brushfire wars and proxy conflicts during that era. One of those conflicts was Afghanistan, where American political leaders basically thought, "A bunch of Fundamentalist Islamic guerrillas with terrorist tendencies can't possibly make the situation any worse than the Commies are, so let's give them a bunch of free guns." Which led to...
The War on Terror: In the fight against terrorism, the US and its allies have shacked up with some pretty sketchy organizations and regimes, justified by how said organizations, for all their corruption, seem more interested in local power than flying airplanes into buildings. Only history can determine how that's gonna turn out.
Goes both ways, really: the presence of the so-called terrorists have caused a lot of powers —some are states, others are not— to align themselves with the US, despite its awful track records when it come to respecting the sovereignty of others. They decide to look the other ways in regard of CIA gulags on their soil.
Why stop with just two ways? The people who suffer from the USA's war on terror —kidnapping, tortures, drone attacks— decide to say "screw that" to their supposed government which have failed to protect them, and align with the so-called terrorists. Even though in any other situation, they won't ever agree with the so-called terrorists' methods. Truly the world is going down a vicious spiral due to the liberal invocation of this trope.
Which has created its own, lesser threshold: if a plane is heading for a civilized area, won't respond to attempts to contact it, and all other attempts to stop it fails, the United States Air Force will shoot down its own country's civilian aircraft. We've already seen what happens when we fail to get there in time.
As a note, the above is basically the entire military history of the 20th century. A country props up a group that they see as the lesser evil to their current enemies, defeat the current enemies and then have to fight the guys they just helped become stronger. Though in all fairness, the current war against terrorists is peanuts compared to what came before; unlike the Nazis and the Soviet Union, these folk pose no threat to the world as a whole.
In a modern conventional firefight (at least amongst the US military), the call of "broken arrow" is this trope. A "broken arrow" scenario means that a battle has effectively gone much worse than anticipated and a unit is on the verge of being overrun. What the call entails is to direct all available attack aircraft and artillery fire on the area being attacked. Because of the close distance nature and general disorganization happening during a "broken arrow" call, friendly fire (also known as Blue On Blue) from airstrikes and artillery is basically expected rather than actively avoided. A realistic demonstration of this was used in the movie We Were Soldiers.
There's also the related call of "danger close," which basically means "I know that I'm close enough to the target that I'm just as likely to get hit as it is, but I want you to fire on it anyway."
Singapore's reserve funds are, proportionate to her market size, one of the world's largest, largely thanks to their usage being handled this way. The one time they have (publicly) been known to be used since independence was during the 2009 credit crunch, which is currently the worst recession since the Great Depression.
Singapore has to get all of its drinkable water from Malaysia. If Malaysia ever cuts the water off, Singapore will, almost without a doubt, immediately declare war.
Singapore's military can also be considered this way; It is not the first country in the world to use a mainly civilian reservist military, but considering Singapore itself (one of the chief primary "export" of this resource-rare country being its relatively small but educated/skilled workforce) the only sane time to use said military (and get most of said workforce killed) would be a "do or cease to exist" situation, such as the above water scenario.
Necessity in Law, which essentially means damage to property and other activities that would normally be against the law may be justified by necessity to prevent some bigger trouble, and a person who has done it is not accountable for it. Factory burning and the only way to get access to one side is through a full car dealership parking lot? Bulldoze the brand new cars out of the way. Sea water bad in the long term for the precision materials and equipment inside the nuclear reactor and will undoubtedly make it unable to be used in the future? Fuck it, we need to cool it down now.
The future United States' Declaration of Independence described political revolution in essentially these terms, and the bulk of it consisted of a list of reasons why the signers felt the actions of the British crown had crossed the threshold.
Since after World War II, the new German constitution includes an article that makes it the duty of all German citizens to use any means neccessary to prevent any government from overthrowing the constitution and establishing another totalitarian regime, which includes the use of armed resistance.
Part of this may have been due to an earlier invocation of thios trope that ended catastrophically for Germany — in the Weimar Constitution, during emergencies, the Chancellor could be allowed to rule by decree if the Reichstag consented for the duration of the emergency. Hitler took advantage of this to take over power following the Reichstag Fire.
Many governments have provisions in law stating that, in a sufficiently serious emergency, most or all rights will be suspended. As far as we know, no government can summon Godzilla, but if they could, this would make it legal.
Related to this: nuclear weapons policy. At least in the UK the military maintains a tradition of letters of last resort. In effect these are the "final orders" to the Captains of the four nuclear-equipped Vanguard-class submarines to be opened in the event of a complete breakdown in command and control as a result of nuclear attack and which nobody knows except the Prime Minister himself/herself. Technically ANYTHING can be ordered but in general the possibilities fall into four categories. One of which is to accept that deterrence has failed and not retaliate and one is to place the submarine under the command of an allied nation. The last two basically amount to the Godzilla threshold in that either a full nuclear retaliation is ordered or, perhaps most horrifyingly, for the Captain to simply "use their best judgement" which in effect amounts to a freedom to do anything he deems necessary.
In the Thai flooding crisis they dug up Bangkok's roads to try and channel away the floodwaters despite the cost in future rebuilding.
Ancient Rome had provisions for this during the Republic: when an enemy appeared invincible and on the verge of overrunning Rome, the Senate chose the man best suited to deal with that enemy and made him a dictator, giving him absolute power for six months and with no legal way to make him pay for anything he did during his term. It usually went well, as they would follow the example of Cincinnatus, who, upon defeating an enemy coalition that had surrounded the Roman army (thus prompting him being named dictator) within the first half of his term, resigned and returned to his farm, and, after being named dictator AGAIN to deal with a coup, he defeated the coup in one day and immediately resigned AGAIN.
Locusts. Old school but still pretty much armageddon to farmers if a swarm manages to grow to Biblical proportions. Crop loss is often expected to be 100% and THEN some. To save even some form of vegetation in the path of a hungry locust swarm means keeping them under a protective, insect proof shell. Expensive and not 100% reliable to say the least.
Methods used to combat locust swarms are usually using enough poison to kill every living thing in the area... except the locust, whose numbers will take a dent but is a hive being several miles wide and thus, can move around, over, or through the poisoned areas.
Worse, it was only in 2009 that scientists even figured out what causes locust swarms to appear. Locusts are grasshoppers - the same grasshoppers that are living in the area already. But if their numbers grow too large, this causes them to literally morph into locusts, swarm, and start eating everything in sight.
Fire. A sufficiently big fire like the Chicago Fire, forest fires, etc., will pretty much turn anything in its path into a smouldering ruin and there is nothing that can be done to stop it. Fires can get so bad, that perhaps the only way to deal with it is to set your OWN fire, the Godzilla Threshold, in the hope that your fire will consume enough fuel/air to fight the original fire. Of course, things CAN go wrong where the fire just merges into one Super Fire.
During the Chicago Fire, dynamite was used to demolish entire blocks of buildings in an attempt to create fire breaks. It was partially successful in some areas, but ultimately they couldn't work fast enough and the fire outflanked the demolition crews. In most modernized countries, building or house fires rarely get to the city-destroying stage anymore, but lighting backfires (which burn towards the original fire, consuming all the fuel) is still a technique in use for fighting forest or brushfires. Setting backfires is reportedly as much art as science, and as previously mentioned is in no way guaranteed to work, making it a controversial tactic at best.
As a number of countries have learned the hard way (the US included) the absolute worst forest fire management policy is to stamp them all out as fast as possible. This leads to build up of fuel until it reaches the stage where it is no longer possible to suppress further fires, resulting in a titanic wildfire, such as the 1988 Yellowstone fire. The better option is to allow natural fires of limited scale to burn, suppressing only fires of large size or human origin. This allows a safe burn-off of the naturally accumulating fuel.
Sometimes the threshhold for fire can be crossed before the fire even starts. After the Americans started their fire-bombing raids against Japan (causing far more destruction and casualties than even the nuclear bombs would later on), the government in Kyoto ordered two large firebreaks to be created in the city by demolishing two wide strips of the city perpendicular to the river (which itself formed another firebreak). Those firebreaks still exist to this day in the form of a pair of wide avenues, alongside some of the oldest urban buildings in Japan (the war ended before Kyoto could be bombed, meaning the firebreaks were ultimately not necessary).
Culling. As stupid as killing an entire farm of livestock or entire yield of crops because ONE animal/batch was found sick sounds, it's because of this Trope that it is done. Depending on what the animal was sick with, Avian Flu, Swine Flu, SARS, or just plain old Foot and Mouth, it is often seen as a good idea to use the Godzilla Option early rather than wait for it to become a Godzilla Necessity. Because as wasteful as culling perfectly good stock is, the potential losses of not doing so are just too great to risk.
And people, at various points in history. Sometimes it has worked, sometimes it hasn't. This was generally before the diseases were properly understood.
In the early 2000's in Wisconsin, Chronic Wasting Disease (the Deer equivalent of Mad Cow) was starting to spread and become a problem. If left unchecked, the disease risked wiping out the deer population to the point where it may not recover. The Wisconsin DNR first tried to find a cure for the disease, or at least find what was causing it in the first place in hopes of preventing further infections. The methods didn't work, so they had no choice: They extended Deer Season by a week and ordered for hunters in the state to shoot more deer than usually allowed in order to thin the numbers to extremely low populations (and to make sure that nobody consumed the infected deer.) Thanks to careful monitoring by the DNR, the deer would recover to normal populations within a few years, and now the disease is barely even a problem anymore.
The Crusades started when the Patriarch of Constantinople asked the Pope for help to fight off the Turks. However, at that point the Great Schism between Roman Catholicism and Eastern Orthodox Christianity was in living memory, and the Pope and the Patriarch had mutually excommunicated each other, each sect considering the other to be heretical. For a religious leader to even consider the help of people he considered heretics, you know it's trope. The aftermath was exactly how you'd expect this trope to go.
If a rocket launch goes really seriously wrong, there comes a point where the best thing that can happen is for the rocket to detonate right now, rather than crashing onto a town and detonating there. It is the job of the range safety officer to recognize when the Godzilla threshold has been passed and push the Big Red Button.
The Deepwater Horizon oil spill of 2010 got so bad and so damaging to the environment that some Russian officials suggested ending the spill permanently by detonating a nuclear weapon at the site of the leak. The reasoning was that the spill had gotten so severe that the damage caused by just nuking it would be less than the damage caused by allowing the spill to continue unchecked. Surprisingly enough, it's actually worked a few times.
Scarily enough, this is what the human body will do to itself when facing a severe infection. The immune response starts with proportionate responses like antibody production or fever... but when that doesn't work, the response gets cranked up to such high levels of inflammation that tissue damage ensues. At a certain point the person might actually die, but can't do anything about their automatic bodily processes shutting down an infection at all costs. What most people don't know its that the majority of modern disease-causing pathogens don't kill in and of themselves- the body does itself in, sort of like how it's Not the Fall That Kills You.
The point of Kate Bornstein's book Hello Cruel World, meant to provide alternatives to suicide for teens; some reviewers complained that said alternatives include things like drugs, alcohol and making a deal with the devil, but the idea is that if someone is considering killing themselves, almost anything, even if not the best choice in general, would be a better option. Then again, the point of the book is not to make the teens self-harm, but to distract them and keep them alive long enough for more "medically accepted" interventions to take place.
For patrol officers in the United States, any situation that requires going to the squad car and grabbing the shotgun or AR-15 carbine is this. It is typically in response to the worst possible situations an officer can encounter, such as a suspect with an automatic weapon shooting at them, or anything else a sidearm isn't capable of handling. Calling in S.W.A.T can also be this, but S.W.A.T teams are also called to situations that simply require additional protection, such as high-risk warrants and security for high-profile operations like major sporting events or visiting dignitaries.