History Main / DangerousForbiddenTechnique

*** And a lasting "fallout" effect that makes it difficult to cast spells in the entire region or a year or more.

* A ''WesternAnimation/BatmanTheAnimatedSeries'' episode has a ninja steal a scroll in Japan that teaches him the secret of a "deadly touch" technique. When Batman faces him off in the end, he tries to avoid being touched by the guy in a specific spot, which (theoretically) would cause instant death. He fails and falls down, seemingly dead. He then gets up and knocks out the bad guy. When asked if the technique was bullshit, he pulls out a [[PocketProtector metal plate]] from under his suit, which has been deformed by a strong force.

** Captain Komamura's clan has the Human Transformation Technique, which turns them from anthropomorphic foxes into full humans with a power boost. [[spoiler: It requires giving up your human heart, and when the technique runs out, leaves the user as a full non-anthropomorphic fox]].

** Captain Komomura's clan has the Human Transformation Technique, which turns them from anthropomorphic foxes into full humans with a power boost. [[spoiler: It requires giving up your human heart, and when the technique runs out, leaves the user as a full non-anthropomorphic fox]].

** The use of Horcruxes is so forbidden that it's nearly impossible to find any information on how to use it.
*** Probably not least because it involves fracturing the soul, and doing ''that'' involves murdering people.

* KamenRiderDouble's Twin Maximum, in which he activates two [[FinishingMove Maximum Drives]] at the same time, temporarily taking his power up to 200%. However, this puts an incredible strain on his body, [[spoiler:as demonstrated when Shotaro impulsively uses it in one battle, which lights him on fire and severely injures him. In the final battle of the series, Double's SuperMode is powerful enough that he can combine the Xtreme and Prism Memories' Maximum Drives without ill effect.]]

* Webcomic/EightBitTheater": '''HADOKEN!!!!'''
** Although not considered forbidden, Black Mage is only able to cast that spell once a day, and it makes a cute little [[NukeEm nuke-sized]] crater wherever he aims it.

* The "Mortal Draw" in ''VideoGame/TheLegendOfZeldaTwilightPrincess''. The attack involved sheathing your sword and untargeting the enemy. As soon as the enemy is within range you quickly pull out your sword and deliver a powerful attack able to one-shot most enemies. However, if you screw up the timing you're going to get hit.

** Nukes are literally forbidden by international law; even ''threatening'' to use nuclear weapons against another power constitutes a war crime. Though eight nations are declared to have nuclear weapons (and one is suspected) most nuclear powers refuse to consider using nuclear weapons unless they someone else does first. Nowadays, the worry is more about the dangers of non-state actors (ie. terrorists) using them instead, which [=MAD=] is essentially powerless against.

* ''{{Castlevania}}: Order of Ecclesia'', blah blah blah, Dominus glyphs, blah blah blah, union kills you dead on the spot [[spoiler: unless you're using it at the end of the last battle, where Albus's soul takes your place for the sacrifice.]]
** To elaborate, Dominus Anger and Dominus Hatred are direct attack glyphs with each use inflicting shitloads of damage at cost to your HP, and Dominus Agony amps all your stats immensely with gradual HP loss thrown in on top of that. Unless you use a healing item at some point, prolonged uses of these glyphs by themselves will kill you. The Dominus glyph union kills everything in the area - Shanoa included save the aforementioned instance - dead on the spot.

** Something else mentioned in the ''Book of Vile Darkness'' is the ArtifactOfDoom called the [[NamesToRunAwayFromReallyFast Death Rock]]. Artifacts are always dangerous, but this one is worse than most; it's history does say that its owners tend to obtain great power and are able to conquer empires, but tend to lose the power at the worst possible time, and are usually overthrown in violent insurrections by their enemies. Here's how the Rock works: It gives the user incredible dark powers of [[{{Necromancer necromancy]], giving him the potential to raise vast undead armies. But it has a terrible cost; once a week, it demands the user slay his closest friend or loved one, and claim him or her as a zombie slave. If he is unwilling or unable to do so, the Rock and all powers associated with it vanish. Clearly, all former users never realize that if you are willing to do this, you're going to run out of friends and loved ones ''very'' quickly (a lot of them will likely stop being your friends before you can use them as the required sacrifices) and be unable to make ant new ones; on the other hand, you'll probably make hated enemies ''very'' fast...

*** Although to be fair, the example from the anime [[OvertookTheManga was just filler]].
*** Lucci even states that if it wasn't for his rubber body, the kind of stress Gear Second puts on Luffy's body would cause his heart to explode.
*** There ''is'' a possibility that Luffy has gained some resistance or outright lost most of the detractions of the technique after Kuma removed the accumulated damage. Post timeskip has yet to go into details though.
** Monster Chopper also qualifies. While he does gain immense power [[spoiler: enough to curb-stomp Kumadori]], he not only loses his sense of self, but also harms himself due to the energy required to maintain the form.
**** [[spoiler: Not anymore: He can now keep control of himself while in this form, though once it wears out he's left pretty much helpless for a while.]]

** In their collective defense, Snowe was really, ''really'', '''really''' hard to forgive. It's not so much that the previous bearers were lacking in forgiveness as it is that the hero has to be a veritable saint just to let Snowe live, much less invite him to join the crew.
** And really, with the Rune influencing events so that, for instance, [[spoiler: a young boy has to choose between using its power or watching his village get burned to the ground by his own countrymen]]... It's pretty much damned if you do, damned if you don't.

*** Not exactly a DangerousForbiddenTechnique in and of itself, but, when the hero offers to use it to power up another rune towards the end of the game, he is ''severely'' chastised by Leknaat, who states that the true power of the Soul Eater must never be unleashed, implying this trope is in effect.

*** [[IThoughtItMeant Oh dude!]]
*** Uh yeah, that's because it takes longer than a day (and it's only a day they spend in Drac's castle), Johnathan shows no ill effects. It's implied that that will come later. He probably won't survive to see Drac's resurrection in 1999 if he keeps using the whip or doesn't somehow lock its power back up. It has also been said that using the whip too much will cause death, making it a possibility that he didn't use it well enough. Jonathan was urged not to over use it by various characters.

* Later on - during the time of ''WesternAnimation/TheLegendOfKorra'' - [[spoiler:Yakone came out to be an AxCrazy Bloodbender who brought fear to Republic City, and even figured out how to bloodbend without a full moon. Then came his sons, both of whom practiced bloodbending frequently and ended up insatiably power driven later on in their lives, especially Amon.]] Therefore the technique was declared illegal.

* In the Marvel universe, there exists a weapon called the Ultimate Nullifier which can RetGone anyone or anything the user chooses. '''''But''''' if the target isn't visualized perfectly by the user, then ''the user'' is the one who gets erased. This is possibly the only weapon that can truly defeat {{Galactus}}. (''Possibly''. He is known to be afraid of it, at least.)

** Quoted above is the Eight Inner Gates, a technique that grants exponentially greater amounts of strength each time one is opened, but with more and more strain on the user's body. Rock Lee, before the timeskip, was almost permanently crippled by using 5 gates and having his arm and leg crushed by Gaara. Might Guy, Lee's teacher, is stronger and more able to use it, but it's indicated that if he opens the eighth gate, death is guaranteed even for him.

--> One hour after the mode is activated, its user will have lost three years of his life! (Or at least he'll be so tired it feels that way!)

*** Monster Chopper also qualifies. While he does gain immense power [[spoiler: enough to curb-stomp Kumadori]], he not only loses his sense of self, but also harms himself due to the energy required to maintain the form.

* In ''Manga/OnePiece'', during the Skypiea arc, there happens to a device called a Reject Dial, which is ten times stronger than the much more common Impact Dial. Using this has a large chance of destroying the user as well as his or her opponent. Wiper, A character intent on killing the Big Bad of that arc with the Reject Dial, uses the item ''thrice'', and though his body does take massive damage, he escapes alive.

** Nukes are literally forbidden by international law; even ''threatening'' to use nuclear weapons against another power constitutes a war crime. Though eight nations are declared to have nuclear weapons (and one is suspected) most nuclear powers refuse to consider using nuclear weapons unless they someone else does first. Nowadays, the worry is more about the dangers of non-state actors (ie. terrorists) using them instead, which [=MAD=] is essentially powerless.