History Main / ForbiddenChekhovsGun

* The Omega 13 from ''GalaxyQuest''. Somewhat played with. None of the characters even ''know'' what it does, including the aliens who built it. So they don't want to use it, because they don't know what it will do.

-->-- ''{{Ghostbusters}}''

* In the ''Film/MenInBlack: Alien Attack'' ride at Universal Studios, a BigRedButton like the one mentioned in the above example appears in every ride car. Like in the film, you are told never to press it. However, by the end of the ride you face a giant alien that's immune to your weapons. Guess what you have to do?
** A cheesy instruction video seen while in line on the ride explains exactly WHY you don't press the button; it's basically a ''nuke'' capable of frying the more {{Kaiju}}-esque aliens.

* At MenInBlack: Alien Attack at Universal Studios Orlando, each player has a small red button under their gun holster that they're specifically told NEVER to push. At the end of the ride, as the car travels into a massive multi-block alien's mouth, Z tells the players to "[[ThisIsSparta PUSH. THE RED. BUTTON.]]". The button activates a subatomic thermal disruptor on the car, and the first player (or players, depending on how fast they are) to press it gets a 100,000 point bonus.

* In the LostInSpace film, ships have hyperspace engines, but it is not a good idea to jump without coordinates or a jump gate as the exit vector would be random. The crew does this anyway when the ship is sabotaged and crashing into the sun.

* ''Film/IronMan 2'' kind of. It occurs when Iron Man and Rhodey fight in Tony's villa they both fire their handcannons at each other at the same time and basically cause a huge explosion, a dangerous side-effect they hadn't predicted. So a ShowDontTell version of the warning. This is then used later on to take out the BigBad when he has the upper hand.

Remember ChekhovsGun that was on top of the mantel? The one Little Bobby was told ''never'' to touch, under ''any'' circumstances? Now's the time to grab it. This is a specific subtrope of the ChekhovsGun where the "gun" is pointed out and ''explicitly warned against using''. It doesn't have to be a MatterOfLifeAndDeath. It can be as simple as being told not to push a button, and later, told to do it.

* In ''ChronoCross'', the BigBad is defeated by literally crossing the time streams.

* ''Film/IronMan 2'' kind of. It occurs when Iron Man and Rhodey fight in Tony's villa they both fire their handcannons at each other at the same time and basically cause a huge explosion, a dangerous side-effect they hadn't predicted. So a ShowDontTell version of the warning. This is then used later on to take care of the invincible enemy.

* An episode of ''{{SpongeBob SquarePants}}'' called "The Krusty Plate" has the titular sponge trying to wash a stubborn spot out of a plate well after the Krusty Krab is closed. Mr. Krabs leaves Spongebob to lock up when he's done, but the platter is so stubborn that Spongebob's efforts last until sometime around sunrise. Spongebob hops into a giant, unexplained turret that shoots beams of soap, water, [[MindScrew and steel wool]] to finish the job, and when that doesn't work, Spongebob has one last resort:
-->'''Spongebob''': [[ShoutOut "It may end life as we know it, but I am crossing the beams!"]]
** Spongebob's efforts [[spoiler:destroy the Krusty Krab, but the spot has finally been cleaned.]]
-->'''Spongebob''': "Look! The platter's clean!"
-->'''Mr. Krabs''': [[YourMom "I'll clean your platter!"]]

Remember ChekhovsGun that was on top of the mantel? The one Little Bobby was told ''never'' to touch, under ''any'' circumstances? Now's the time to grab it. This is a specific subtrope of the ChekhovsGun where the "gun" is pointed out and ''explicitly warned against using''. It doesn't have to be a MatterOfLifeOrDeath. It can be as simple as being told not to push a button, and later, told to do it.

Remember ChekhovsGun that was on top of the mantel? The one Little Bobby was told ''never'' to touch, under ''any'' circumstances? Now's the time to grab it. This is a specific subtrope of the ChekhovsGun where the "gun" is pointed out and ''explicitly warned against using''. It doesn't have to be life or death. It can be as simple as being told not to push a button, and later, told to do it.

* ''{{Ghostbusters}}'' has the iconic warning "Don't cross the streams," which they inevitably have to do at the end of the movie. As former TropeNamer, it was also causing confusion, since this overlaps with GodzillaThreshold. In this case, the non-disaster when do end up crossing the streams makes internal sense: they are firing into a [[spoiler:ParallelUniverse and presumably, [[InferredHolocaust the disaster Egon predicts happens]] '''[[InferredHolocaust there]]''' - and closes the gate]].

* ''{{Ghostbusters}}'' has the iconic warning "Don't cross the streams." As former TropeNamer, it was also causing confusion, since this overlaps with GodzillaThreshold.
** Note that in this movie, the non-disaster when they are Crossing The Streams makes internal sense: they are firing into a [[spoiler:ParallelUniverse and presumably, [[InferredHolocaust the disaster Egon predicts happens]] '''[[InferredHolocaust there]]''' - and closes the gate]].

** [[ConspiracyTheorist That's according to weirdos and "pseudoscientists"]].

* ''Film/IronMan 2'' kind of, it is portrayed when Iron Man and Rhodey fight in Tony's villa they both fire their handcannons at each other at the same time and basically cause a huge explosion, it is obviously meant to be a dangerous side-effect they hadn't predicted. So a ShowDontTell version of the warning. This is then used later on to take care of the invincible enemy.

* Happens again in ''GhostbustersTheVideoGame'', [[spoiler: except this time due to being in the ghost world - where the same rules of physics don't apply, such as the lack of gravity on the actual landmass - one can probably assume that you can [[CrossingTheStreams cross the streams]] without frying your ass to bits because the chances are ''reversed'', thus making it more safe to try.]]

* The Higgs particle. The way to discover it ''could'' turn Earth into a black hole.

Remember ChekhovsGun that was on top of the mantel? The one Little Bobby was told ''never'' to touch, under ''any'' circumstances? Now's the time to grab it. This is a specific subtrope of the ChekovsGun where the "gun" is pointed out and ''explicitly warned against using''. It doesn't have to be life or death. It can be as simple as being told not to push a button, and later, told to do it.

* In the ''{{Warhammer 40000}} BloodAngels'' novel ''Deus Sanguinius'', in order to [[spoiler: use the full power of the Spear of Telesto, Rafen]] willingly embraces the Black Rage and is saved from falling irreversibly into it.

* Subverted in ''{{Lord of the Rings}}''; i.e. the Ring ''can't'' be used, even as a last resort, because such absolute power would also corrupt the user, while the temptation alone corrupts the will, and so it ''will'' eventually be used even if merely kept safe. Thus the only solution is to destroy it.
** Played straight with Moria

* Subverted in the ''Series/DoctorWho'' episode "The Parting of the Ways": the Doctor has devised a "Delta Wave" that will wipe out the entire Dalek fleet - but, as the Emperor of the Daleks mockingly reveals, he doesn't have enough time to refine it, and so it will kill every human on Earth in the process. Knowing that there are colonies of humans elsewhere, the Doctor is about to use it... but then, as the Emperor asks him whether he is a killer or a coward, [[CrowningMomentOfAwesome he turns away from the device, declaring, "Coward. Any day."]]
* Brilliantly done in the ''StarTrekEnterprise'' episode ''Twilight''. Archer is afflicted with bizarre brain parasites that prevent him from gaining any long-term memories. Phlox spends years trying to find a cure, describing his research as needing an anti-matter reaction that wouldn't kill him in the process (the fuel used in a warp engine). In a surprising discovery, Phlox finds that the parasites are out of normal time, so killing them now kills them in the past (which would [[SetRightWhatOnceWentWrong change some very bad things]] that had happened [[ResetButton in the intervening years]]). The Enterprise is about to be incinerated by enemies, when Archer hits on an idea: blow up the ship's warp engine, which will predictably release a ton of anti-matter. Phlox and T'Pol point out the side-effects, i.e. the ship and them being killed, but as Archer points out, what other option is there?
** In essence, Archer was reasoning (in usual ST Universe logic) that if they did it, this entire "timeline" ''would never have existed to begin with''. Janeway made a similar calculation, and came to a similar conclusion with similar results (i.e., ''kaboom'' goes her ship), in the ''StarTrekVoyager'' episode "Year of Hell".
* In ''PowerRangers'', when Kim travels back through time, she is forced to recruit her teammates' [[IdenticalGrandson Identical Ancestors]] to become WildWest Power Rangers to protect Angel Grove from the MonsterOfTheWeek that followed her back. Zordon strictly forbids Kim giving ''her'' identical ancestor that time period's Pink Power Coin, saying "Too much pink power can be '''very''' dangerous." Considering Big-Z was cool with dispatching über-destructive giant robots into heavily populated areas, it's generally held as strict {{Fanon}} that doing so would have truly catastrophic results, and that this is why you never have two Rangers of the same color/power source on the same team.
** Subverted in the episode "Forever Red", wherein all TEN RED RANGERS (at that point) come together to fight the monster of the week. Possibly justified, however, in that the ten Red Rangers were drawing from separate power sources, and the vast majority were from separate teams.
* RedDwarf:
-->'''Kryten''': If this works, it'll age those manacles by half a million years.\\
'''Lister''': And if it doesn't?\\
'''Kryten''': It'll wipe out the universe.
* On the [[StarTrekTheOriginalSeries ''Star Trek'']] episode "The Naked Time," a deranged crew-member shuts off the warp-engines, and it takes 30 minutes to heat the anti-matter; but the ship will crash in 17. Scotty tells Kirk that you can't mix matter and anti-matter cold, because it'll destroy the ship; Kirk orders them to do it anyway, and ends up inventing time-travel.
* [[BabylonFive Babylon 5]]: The "Bonehead Maneuver" as mentioned in the Season 3 premiere. Basically, you have two ways of going in and out of hyperspace. If your ship is powerful enough, you can open your own jump point, or, if your ship isn't that powerful, you have a Jump Gate open one for you. You never want to open a jump point inside a jump gate, because this causes one massive explosion of a NegativeSpaceWedgie. Aside from the loss of a very hard to replace jump gate (typically a star system will have one at most) and potentially stranding people in the system if they lack massive starships, this doesn't actually cause any huge universe-altering affects. Just a huge explosion that is difficult for most ships big enough to open a jump point to [[OutrunTheFireball outrun]]. They end up using the trick in a tricked-out new spaceship that MIGHT be fast enough to get away after using this trick to kill an enemy they DEFINITELY weren't big enough to fight.

* The Manhattan Project. Scientists did experiments seeing how close they could get radioactive cores to going critical without ''actually'' making them go critical. They called this [[TemptingFate Tickling The Dragon's Tail]], and considered it a necessary but insanely dangerous thing to do. One core did accidentally go critical (very briefly) on two seperate occasions, resulting in the deaths of two researchers and less severe cases of radiation poisoning for several others. They dubbed this one the [[NamesToRunAwayFromReallyFast Demon Core]].

** Before the Manhattan Project, some scientists theorised that an atomic bomb could theoretically lead to a chain reaction that would involve the entirety of Earth's atmosphere, leading to a literal EarthShatteringKaboom. This is due to ScienceMarchesOn, as the modern knowledge of physics tells us that it couldn't have happened, but back then, it was this trope.

* ''MagicTheGathering'' has several cards that do the equivalent of crossing the streams, such as [[http://ww2.wizards.com/Gatherer/CardDetails.aspx?id=14500 Armageddon]], [[http://ww2.wizards.com/Gatherer/CardDetails.aspx?id=41168 Akroma's Vengeance]], and [[http://ww2.wizards.com/Gatherer/CardDetails.aspx?name=Wrath_of_God Wrath of God]]. The thing is that skilled players set up their decks so that they have the least to lose, which makes these cards almost an aversion.
** Those cards will hurt you, but they don't run the risk of directly killing you. Cards like Lich, Doomsday, and Final Fortune do. A ''true'' example of Crossing the Streams in [[MagictheGathering MtG]] would have to be a play, though, not a particular card (remember, cards are there because you intend to use them, and Crossing the Streams is something that you planned to ''never'' do). Example: attacking with a Flesh Reaver when both players are at 4 life, and hoping to hell that your opponent doesn't have a Simplify (or something equally ridiculous) that they can cast just to gain 1 life from their Wooden Sphere. Or casting Shatterstorm to kill your own Covetous Dragon, which can't attack until next turn for whatever reason, so you can throw its corpse at your opponent with Balduvian Dead on ''this'' turn.
** [[http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=130680 Intervention Pact]] and its 4 friends in the other colors could be considered a Cross the Streams moment, if you don't have the mana necessary to pay the cost next upkeep. If you don't win the game by then, the {{Temporal Paradox}} you created (your future self from your next turn cast the spell that just saved you, but now it's your next turn and there's no way for you to cast that spell!) blows you up.
*** And then someone figured out the Pact of the Titan/Hive Mind combo, which involves forcing you and your opponent to set up the same temporal paradox, and making sure their debt is called in first.
* ''{{Warhammer 40000}}'' gives us Prince Yriel, who saved his Craftworld from being eaten by Tyranids by grabbing [[ArtifactOfDoom the Spear of Twilight]] out of stasis, beating the Tyranids but dooming himself to death from a wasting curse.

* Pretty much the point of having [[Comicbook/IncredibleHulk the Hulk]] in Comicbook/TheAvengers. While Banner's genius is useful, the real reason he's around is to have an emergency backup plan: Let the Hulk loose.
** Which they finally did during the climactic battle against Onslaught. And Onslaught was so powerful it almost didn't work--until the other heroes [[spoiler:manage to [[PowerLimiter separate Banner's persona from the Hulk]], allowing him to use his full power and destroy Onslaught.]]
* Bane's [[PsychoSerum venom]] in SecretSix.

* ''{{Ghostbusters}}'' has the iconic warning "Don't cross the streams." Note that in this movie, the non-disaster when they are Crossing The Streams makes internal sense: they are firing into a [[spoiler:ParallelUniverse and presumably, [[InferredHolocaust the disaster Egon predicts happens]] '''[[InferredHolocaust there]]''' - and closes the gate]].
* The 2004 ''Comicbook/FantasticFour'' [[Film/FantasticFour film]] showed the Human Torch increasing his flames to potentially world-ending temperatures to defeat Doctor Doom. It doesn't end the world, of course; [[SciFiWritersHaveNoSenseOfScale not that it really could.]] Just to prevent any catastrophe, the flaming happens inside a forcefield created by the Invisible Woman.
** In the follow up, physical contact between Johnny and his teammates has caused a variety of unpredictable consequences due to power switching but at the end, they decide to risk all touching at the same time which pays off giving Johnny all their powers to fight a souped up Doom.

** It may have just been a deterrent by K to keep J from fiddling with it, considering J's predispositions. It's not necessarily "dangerous", more "conspicuous and a pain in the butt for Special Services to clean up after".
** In the second movie Jay uses "Pressed the Red Button" as a type of code, indicating that it is reserved only for the biggest emergencies. They seem to prefer to not even use the neuralyzer if they don't have to, so going for a rocket car ride would likely be a last ditch number on their list of priorities.
* The Omega 13 from ''GalaxyQuest''. It's actually "used" ''before'' the characters learn its destructive potential — in the ShowWithinAShow, that is.
* In ''ToyStory'', it's an unwritten rule that toys are inanimate around humans. Even Buzz follows it, though he believes himself the real thing. In order to save Buzz, Woody and the other toys freak out Sid by coming to life in his presence.

* ''Film/IronMan 2'' kind of, it is portrayed when Iron Man and Rhodey fight in Tony's villa they both fire their handcannons at each other at the same time and basicly cause a huge explosion, it is obviously meant to be a dangerous side-effect they hadn't predicted. This is then used later on to take care of the invincible enemy.

* Terry Brooks plays this straight in most of his fantasy novels, especially the ''{{Magic Kingdom of Landover}}'' series. Generally, his protagonists have access to powerful magic that defeats or destroys their enemies. However, every time they use it, they get a feeling that one day, they will [[WhatHaveIBecome "lose themselves"]] to the magic. This of course never happens.

* Averted in ''{{Discworld}}'': a potentially world-destroying spell has lodged itself in Rincewind's mind. He doesn't know exactly what it does, but he knows he should only use it as a last resort. He ''almost'' uses it several times through the course of ''Discworld/TheColourOfMagic'', but doesn't [[spoiler:until the end of the next book, ''Discworld/TheLightFantastic'', when it turns out it's '''not''' a spell to destroy the world... but to create others.]]
** Much later in the {{Discworld}} series, in the back-story of ''Discworld/GoingPostal'', an automatic letter-sorting device with extradimensional components goes out of control, filling the Ankh-Morpork Post Office entirely with letters. Wizards called in to inspect the device warn that shutting it down is likely to destroy the universe. Unconvinced, a veteran mail-carrier gets fed up, and smacks the device with a crowbar until it shuts down. Subverted in that the wizards insist that the universe ''really was'' destroyed, but was instantaneously replaced by a complete, identical universe.
*** Of course, that exact thing has actually happened before in that series. Twice.
*** Also subverted by the fact that when the mail-carrier started hitting the device the wizards ran away. As the doer of the deed testified; unless they had some other universe to run to they weren't really sure about the risk.
*** The only problem with the letter sorter was that it was built around a wheel whose circumference was exactly 3 times its diameter.
*** The REAL problem with the letter sorter was it was built by [[BunglingInventor Bloody Stupid Johnson]].

* Aban from ''DaiNoDaiBouken developped'' [[DangerousForbiddenTechnique Grand Cross]] as this (he specifically states that it's only intended to be used when everything else has been tried). The skill uses life force as a weapon, and is supposed to put one's life on the line. Then, Hyunckel started to realise he had an impressive survival rate when using it, and it became one of his main skills in ''regular battles''.
** Interestingly enough, when [[spoiler: Aban finally decides to use Grand Cross at the end of the manga, Hyunckel disapproves and [[LampshadeHanging lampshades]] the situation: Aban wouldn't be able to use Grand Cross without risking his life. Then Hym, who ''knows'' his body won't be able to resist the skill, does it anyway to shut them both up]].
* The human race does something similar in ''TopWoNerae!'' (a.k.a. ''{{Gunbuster}}''), sacrificing the entire planet Jupiter and a good chunk of the galactic core to destroy -- or at least severely slow -- the progress of the ''Uchuu Kaiju'' (literally, "Space Monsters"). It was their last resort, and there was always the risk it wouldn't work, or it would work too well.
** In ''TopWoNerae! 2'' (''Diebuster''), they try a similar stunt using the Planet Earth as a giant battering ram. Luckily, the title HumongousMecha shows up to stop it and save the day.
* ''{{Slayers}}'' offers another example with the Giga Slave. On learning, after having used it once, that the spell could cause the world to turn to chaos, she vows to never use it again; naturally, she's forced to do so at the end of Slayers Next.
** Interesting to note, however, is that it's not always used. The end of the first season, like the end of NEXT, is one big attempt to get her to perform the spell. She doesn't. Almost the entirety of Try, once the characters learn who the BigBad is, is about finding a way NOT to use it. They succeed, but Lina always accepted that she may have to use the Giga Slave if thier plan didn't work.
* In ''SaintSeiya'' the Athena Exclamation is a forbidden technique with the power of the Big Bang, that needs to be performed by three Gold Saints. Even worse, if two Athena Exclamations collide, it will destroy everything. When this actually happens, it takes a third party to interfere and redirect the techniques elsewhere.
* Releasing a Lord in ''ShakuganNoShana'' floods the body of the Lord's Flame Haze with so much raw power that it kills the user. [[spoiler:Except for Shana, whose body is strong enough to contain all that power.]]
* The God Phoenix's Bird Missile in ''[[Anime/ScienceNinjaTeamGatchaman Gatchaman]]''. Condor Joe CONSTANTLY suggests firing it at the MonsterOfTheWeek, but Eagle Ken always stops him, much to his chagrin. When they finally face a threat so big that they DO fire it, it's an absolute [[OhCrap "OH SHIT!!"]] moment for Joe: he never DARES question Ken about firing it from then on. Ever.

* In the ''{{Flash}}'' storyline "Terminal Velocity", Wally has various reasons to believe that pushing his superspeed too far will draw him into the Speed Force, never to return. He tries to avert a conflict which he knows will force him to do this, but to no avail. However, when he does finally enter the Speed Force, he manages to return (which no one has done before) thanks to ThePowerOfLove.
* In the {{Asterix}} comics, Getafix does not allow Obelix to drink the magic potion, as he fell into the cauldron as a boy, and an extra helping could have bad effects on him. But in ''Asterix and Cleopatra'' (both the comic book and the animated version) Getafix gives him just a drop of potion to give him extra strength in a difficult situation.
** They would die if they didn't get out, so it was a risk worth taking.

The only thing that will win the day is also the one thing that the heroes have been trying to ''avoid'' doing, because it's too dangerous. This is usually ''not'' something that's been intentionally held over as a last resort; [[GodzillaThreshold it only really becomes an option]] when all your ''other'' last resorts have already been tried, and there's nothing left but "that one tactic that could kill us all if we use it." It is usually in regards to an immediate need to kill the villain / save the world / be BigDamnHeroes.

In general, whenever someone says "Don't touch that, it's in case of ''extreme'' emergencies", it '''''[[ChekhovsGun will]]''''' be used in an extreme emergency later on. As a desperation maneuver, it invariably works. (Remember, [[MillionToOneChance desperation maneuvers ALWAYS work]].) In fact, if a character at any point says, "Don't ''ever'' do that!", it's ten to one that very thing ''will happen'' by the end of the story (whether on purpose or by pure accident).

This is a subtrope of ChekhovsGun and its variants. ExplosiveOverclocking is often a variant of this. ''Mildly'' related to TemporalParadox, GodzillaThreshold and FinishingMove. Compare DangerousForbiddenTechnique or EleventhHourSuperpower.

(However, it also involves an "ethical handwave" if it endangers more than it offers to save, i.e. if something might destroy the universe while killing the BigBad, so the "heroes" risk destroying the universe just to save themselves and win their own personal squabble.)

* Named after the most famous example of the trope, ''{{Ghostbusters}}''. Note that in this movie, the non-disaster when they are CrossingTheStreams makes internal sense: they are firing into a [[spoiler:ParallelUniverse and presumably, [[InferredHolocaust the disaster Egon predicts happens]] '''[[InferredHolocaust there]]''' - and closes the gate]].