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Pokémon's Team Rocket trio has had a few moments of this, such as when Delibird accidentally healed a critically wounded Pikachu.
In Pokemon Special, there seriously should've been no way for Sapphire to come out on top when in an airtight Drowning Pit. The bad guy there with her (who provided himself a means to breathe) could have simply waited a couple minutes until she ran out of air. But no, he provided her with the means and time to escape by bringing out his Sharpedo, letting her break its teeth off, and not noticing her using said teeth to cut open a hole in the wall. Needless to say, he got owned pretty damn badly.
Digimon Adventure's Devimon, the series' first Big Bad, accidentally triggers the one Digimon that could beat him into Evolving/Digivolving by threatening its partner's life. Vamdemon/Myotismon was strong enough to beat all seven of the Chosen Children/DigiDestined and could have done so, if he hadn't spent so much time searching for the eighth, and allowing her to find her Digimon.
It gets even more ironic considering Vamdemon/Myotismon that he trained Tailmon/Gatomon to begin with and brought her to the human world, allowing her to meet her partner. He then kills Wizardmon directly in front of her, allowing her to evolve into the one Digimon predestined to kill him. If he'd just left her wandering the Digital World, he'd have won.
Piemon/Piedmon of the Dark Masters falls here. In taking his sadistic pleasure in dealing with the Chosen Children/DigiDestined, he causes Angemon to finally evolve into Holy Angemon/MagnaAngemon who proceeds to undo his magic, allowing the Chosen Children/DigiDestined to kick his butt, ending with him being sucked into Heaven's Gate/Gate of Destiny...which, considering Digimon live forever unless they're killed, was a Fate Worse Than Death.
In Digimon Adventure 02, BlackWarGreymon nearly suffers the same fate when he slams Angemon against a holy artifact.
In Dragon Ball Z , Frieza had survived a Spirit Bomb, the heroes were out of battle power, and Piccolo had just been given a near-fatal injury. Just for fun, Frieza decides to implode Kuririn/Krillin. Unfortunately for him, this triggered Goku's rage enough that he was able to turn into a Super Saiyan. Frieza then gets his ass handed to him. Oops.
And again when Cell tries pressing Gohan's Berserk Button. He uses his Cell Juniors to pound the Z-Warriors to hell. This, along with him crushing Android #16's head right in front of him causes Gohan to reach Super Saiyan 2. This was an instance of Be Careful What You Wish For, as Gohan had warned him about what would happen if he made Gohan lose his temper. At least Frieza and the audience at the time didn't know that it would lead to the Super Saiyan transformation; Cell, meanwhile, was an incurable perfectionist and wanted to fight his opponent at his strongest, believing himself to be incapable of losing due to being...well, perfect. You'd think that since he had some of Frieza's cells, he would have learned from his mistake...
Yu-Gi-Oh! GX: Brron. He thought by killing Juudai's friends, he would be able to defeat Juudai. Instead, it unleashes Juudai's Unstoppable Rage and the secret powers of darkness within him and Brron gets stomped flat. Then Juudai goes on to be an even bigger villain himself. Thanks, Brron! Couldn't have saved the world without you!
Of course, Brron was working under Yubel, and bringing out Judai's dark side is what Yubel had actually wanted, but she couldn't have predicted the end result of it. (Which actually caused her to achieve her goal - just not in the way she had planned.)
Note to V.V. from Code Geass. When you send out an assassin, make sure he has no unrequited loyalties to the matriarch of the target. You just might have a Heel-Face Turn in the works.
Had V. V. not murdered Marianne, Lelouch may have never stumbled upon his parents' Ragnarok Connection plan.
Hell, had V.V. not murdered Marianne, the entire plot would never have come to pass.
And when assigning a loyal assassin to act as a safeguard against possibly rebellious people that you're using in some diabolical plot under the cover of being their sibling... Don't make their cover so good that even they forget that they aren't a loyal, loving brother.
In Space Pirate Mito, Aoi wears a bracelet that he believes is a good luck charm and the audience is lead to believe is the key to a powerful weapon. He also starts having random bursts of powerful energy when the bad guys attack. Near the end of the series, Ranban removes this bracelet and tells Aoi it was an enhancer that brought out his powers, making him helpless without it. Cue Aoi causing an explosion with power even greater than he used before, and Mito telling Ranban that the enhancer was actually a limiter to keep Aoi's powers in check.
Sesshomaru has a tendency to inadvertently help Inuyasha almost every time he fights him. His attempts at obtaining Tessaiga for himself led to losing an arm, Inuyasha getting it, and subsequent attempts to take it help Inuyasha master it. However, it becomes increasingly obvious that Sesshoumaru is moving away from this trope into I Was Just Passing Through as begins warming up to his brother (in a The Only One Allowed to Defeat You sort of way).
Late in the story, Sesshoumaru's hit rock bottom, lost his weapon and Naraku realizes that now is the time to take back the last shard by sending out the evil spirit of the Shikon Jewel to destroy Sesshoumaru. Magatsuhi utterly curbstomps both Sesshoumaru and Inuyasha before discovering that stabbing Sesshoumaru through the chest doesn't kill him. Instead, it pushes his powers beyond his known limits into a level even he didn't know he possessed. Conclusion? Naraku makes one of the strongest characters in the story even more powerful. Oops?
In the anime, Bankotsu and Inuyasha have been repeatedly fighting to a stalemate, with Inuyasha unable to use the Backlash Wave because Bankotsu is not a demon. In their final fight, however, Bankotsu manages to bring his demon kill-count up to 1000, upgrading his Banryu into a demonic weapon...which finally allows Inuyasha to use the Backlash Wave to reflect its strongest attack, shattering the weapon and finally defeating Bankotsu.
In the Dark Tournament arc Toguro "kills" Kuwabara so Yusuke will be able to fight at 100%, somewhat subverted because he knew exactly what he was doing and would probably end up losing.
Ironically, Sensui wanted to die at the hands of a demon, so his actions worked out perfectly.
Yeah, one of the big themes from the moment Younger Toguro appears is the concept of what is more important: Victory or the fight itself. Pretty much everyone does this to some degree, and about 75% of them were intentional.
In Naruto,Pain has Naruto utterly beaten, pinned to the ground and paralyzed. When Hinata jumps in to try and save Naruto, Pain blows her away, knocking her out. Then, just to make a point about suffering (or possibly just to be a dick), he stabs her, apparently fatally. This triggers Naruto's Unstoppable Rage, going straight to 6-tailed form for the first time, Do Not Pass Go-style, then eventually to 8-tails, and tempted to go fully to 9. Presumably Pain thought he could win, since his ability was keeping Naruto paralyzed and with disrupted chakra. He would have been dead wrong if the 4th Hokage's safeguard hadn't brought Naruto back from the brink but even so it directly brought about his own defeat by freeing and reempowering Naruto. Nonetheless, when Naruto finally snaps out of it, Pain isn't nearly as confident anymore.
Mizuki's attempt to get Naruto to steal the scroll for him by promising to let him graduate if he learned a technique off of it ended up helping Naruto learn the Shadow Clone Jutsu, which comes into play in most of his other techniques, and enabled him to graduate from the academy despite the fact that his promise was insincere.
The equivalent moment in the manga for Kid fits the trope - Mosquito Curb Stomping him triggers his questionable Super Mode, but Black Star's final fight with Mifune does not. Black Star had already been 'fixed' by his negotiation with Nakatsukasa/Masamune and the Single Stroke Battle sequence which ends his fight specifically, IIRC, does not involve an Super Mode.
In Mirai Nikki, the sixth diary holder, Tsubaki plants a Take-That Kiss upon protagonist Yukiteru right in front of his Yandere partner, Yuno. Cue Death Glare. Thinking everything's gravy, Tsubaki checks her diary and sees that it predicts her imminent death. Oh, Crap.
In Fullmetal Alchemist, Major Armstrong is injured in his fight against Sloth, until Sloth delivers a blow that accidentally pops his shoulder back into place, giving Armstrong his second wind.
Though Armstrong probably deliberately placed himself so that Sloth would attack in such a spot that his shoulder popped back.
During Roy Mustang's raid on Central City, he takes Mrs. Bradley hostage. The soldiers sent after him are told to kill everyone except him, since the villains need him for their plans. The fact that the military is willing to kill Mrs. Bradley makes it easier for Mustang's group to win the support of the populace, and suggest that the Central city soldiers they're opposing are fighting against the current regime.
Pride would've assimilated Ed's body, if he hadn't made a point about Homunculi superiority at the wrong moment, causing Kimblee to stop him because he really doesn't like hypocrites. Speaking of which, eating Kimblee was also a bad idea in hindsight, since he proved to be crazy enough to retain his identity after being absorbed into Pride's Philosopher's Stone.
But bigger and longer in the making than all of the above would have to be the series Big Bad, who caused his own downfall by one act of kindness. The Dwarf in the Flask (AKA: Father) saved Hoenheim from becoming a human sacrifice along with the rest of Xerxes and split the resulting philosopher's stone with him, which extended Hoenheim's lifespan well beyond its natural end (both as thanks for being the reason he existed, as Hoenheim's blood was used by an alchemist to create Dwarf in the Flask). Without that, Hoenheim never would have had the opportunity to set up the giant reverse transmutation circle that gave the heroes the chance they needed to fight back in the end. Not to mention fathering Al and, more to the point, Ed, who ultimately foil the Big Bad's plot.
In Jack And The Witch, Squeaker the Mouse, now turned into a ghostlike harpy, taunts his imprisoned animal friends by making them watch a crystal ball showing their human friend Jack (plus his ally the harpy Allegra) being tormented by the vicious Harpy Queen; in the course of his teasing he knocks the ball loose, letting it roll, fall, and shatter, thus destroying the Queen's power and freeing the others.
Kyubey in Puella Magi Madoka Magica pushes Madoka to make a contract with him, and make a wish, because he knows she will make an extremely powerful magical girl. In the process of trying to break her, he reveals the existence of magical girls throughout humanity's history, and that they all died in despair. When she finally agrees to the contract, her awareness of the suffering that has happened in the past drives her to force through a Cosmic Retcon - which Kyubey has no choice but to grant. On top of that, the only reason she's so powerful in the first place is because he granted Homura's wish to save Madoka in such a fashion as to send Homura off on her quest through alternate universes, each of which adds a bit more to Madoka's power...
In the PSP game, his inability to understand emotions can cause his actions to calm the girls down instead of breaking them down, thus preventing them from becoming witches.
In Shakugan no Shana, during Season 2, Hecate, one of the villains, infiltrates the school that Yuji is going to through a sort of poorly disguised covert agent named Konoe. Konoe then tries to get close to Yuji, much to the consternation of Shana and Yoshida. While gathering feelings and emotions, one thing that Konoe discovers is that birds seem attracted to her, and she often reaches out with her hand to let them land, making her happy. Later on, this comes back to bite Hecate in the behind when said memory inside the Statue of Pride triggers when it sees Shana flying towards it, looking like a little bird. Instead of attacking her like it had been, the statue instead reached out with its hand, allowing Shana and Yuji the opening they needed to reclaim the Reiji Maigo from it, as well as defeating said statue. Cue Hecate looking on in shock and wondering exactly what just happened.
Muhyo And Roji, after their time apart, are faced with the task of getting their office back from Goryo's group. Luckily, around this time, Ark kidnaps Goryo, and after Muhyo and Roji save him from Ark, Goryo returns their office in return.
In the Arcanum arc, while Roji is having some difficulties with Muhyo, The Mole tells him a story that causes him to realize that Muhyo is pushing himself as hard as he is for Roji's sake and the belief that he can improve. Roji does manage to make effective contributions to the next battle. The Mole later points out that the help was to ward away suspicion and that Roji's talent was an unpleasant surprise.
In episode 19 of Magical Project S, Ramia has transformed Misao into Misa in the day where her father comes to visit her. Her plan not only fails, but also leads Sasami and Misao to have angst of discovering their magical girl identities.
In the "Deicide" arc of Bleach, Big Bad Aizen destroys the cleaner that patrols the Precipice World between the living world and the Soul Society. Because the Precipice World has heavily dilated time, this gives Ichigo the chance to train and develop his ultimate technique. Aizen later reveals that he did this on purpose, in the hopes of creating someone who could match him. It works.
Aizen's been doing this even before Ichigo's conception. By releasing the proto-arrancar "White" into the living world, he caused Isshin and Masaki to meet. Ichigo literally would not have been conceived if not for Aizen (something Aizen was well aware of), and his existence caused Aizen to facilitate his growth out of hope of creating an opponent that would allow him to attain a higher level of transcendency once he merged with the Hogyoku. Meaning the entire plot for over half the series is an example of this.
In episode 4 of Fight Ippatsu! Juuden-chan!!, a thief breaks into the school where Hakone and Iono attend. He steals both the student council's funds, along with Iono's gift to Sento, Hakone's brother. Plug and Sento decide to help Iono out of her depression by trying to find the thief, but have no luck whatsoever. Arresta, a coworker/rival of Plug, meanwhile watches them a little bit, then decides that while its noble of him to help her out, she's got a job to do. She decides to continue her job of zapping people, and one of the people she zaps suddenly decides he's going to turn himself in. Although she's wondering what the heck she just did, she inadvertently caught the thief and helped recovered the stolen money and Iono's gift.
In Tiger & Bunny, Mr Maverick pats Kaede on the head when he meets her, unwittingly transferring his memory-altering power to her. This later allows her to restore the memories that Maverick had scrubbed from the heroes as part of his plot to frame Kaede's father for murder. Thanks, Mr. Villain!
In the hentai short Demon Princess Birth by Inoino, the heroine is captured and raped by ogres, with her powerless to resist, but this causes her to turn into a succubus. The final page has her inflicting Out with a Bang on them.
During the finale of .hack//ROOTS and revisited in the first volume of .hack//G.U., if not for encountering TriEdge/Azure Kite in the Hulle Granz Cathedral and being data drained, thus being reverted to a low-level Player Character and losing his brokenclass upgrade, Haseo might have never been able to properly control Skeith or calm his head enough to stand any chance against the real threats he would have to face. note Word of God is that TriEdge/Azure Kite was actually aiming for Ovan behind Haseo, but it still worked out.
In Honoo No Alpen Rose, the maid Anna is an accomplice of Manipulative Bastard Toulonchamp, whose plans relay on his daughter Mathilda acting as the Body Double of female lead Jeudi. Thing is, at some point Anna attempts to murder Jeudi via dropping a flower pot on her head... but fails, and Jeudi "merely" gets her ankle hurt. This very dumb move not only alerts the people around about how far Toulonchamp is willing to go (which reduces their willingness to collaborate), but it also scares the crap outta Mathilda herself and pushes her to drop part of the truth on Lundi... and it starts to plant the seeds of doubt in the heart of Jeudi's Ill Girl mother Helen.
Want to know how Fist of the North Star's Kenshiro ended up joining in the race which would lead him to becoming the 64th successor to Hokuto Shinken? His elder brother Raoh started teaching him Kung Fu when he was a kid.
Played pretty much straight with Gauron from Full Metal Panic!, of all people. Despite all that he's done and/or tried to do to Sousuke, his words end up have an eventually positive impact on the kid. For example, his lecture in TSR contains not only vital information that he willingly passes on to Sousuke (in order to get revenge on his former organisation, but mostly "as a favour to you"), but it also poses Sousuke one of the most important questions in his personal arc: "Did you sell your soul to those bastards in Mithril?" Sousuke gives his answer during his confrontation with his Mithril superiors at the end of TSR: "I dont' remember selling my soul to you." Also, on every occasion after Gauron's death (uh... the final, definitive one, I mean...), that someone mentions Gauron, it only serves in making Sousuke try harder. He uses his 'Kashim' personality to reach his goals, knows some of his enemies better because they were Gauron's associates (and they fear/respect him because they know how Gauron... felt about him) and he eventually confirms his and Gauron's almost identical nature to Leonard Testarossa's face, with no shame or guilt, merely pointing out the one thing that made them different: the enjoyment they each took in the act of killing (or lack thereof, in Sousuke's case). And in hearing Leonard's words about Gauron's opinion on the delicate subject of changing history/fate, Sousuke received confirmation of his own beliefs (apparently, he trusted Gauron's judgement on this matter, at least). All in all,not a bad job from the resident psychopath of the series.
In Mai-HiME, the Obsidian Prince goes to great lengths to make sure Mai wins the Festival. He also has Mikoto in reserve in case Mai won't join him. But for that to work, he needs Mikoto to be willing to kill her — and he himself had just finished convincing Mikoto that Mai would still forgive her! (This was part of the plan to eliminate another HiME.) She might still have done it if Mai had been really out for blood, but the prince should've known her better than that.
In Attack on Titan, Eren points out the greatest mistake of Annie, Reiner and Bertolt was teaching him how to fight.
Had Annie/the Female Titan not spared Armin's life as the former was slaughtering soldiers, he would have not figured out her identity.
In the movie Uchuu Senkan Yamato Revival, the crew of the titular ship were stopping to watch the last moments of the Earth, which was in the path of a rogue black hole. Cue the villain of the film, whom they thought they had already defeated, showing up to taunt them about how they had been the ones to send that black hole at Earth, in order to pull it into their universe. Cue Kodai and the crew, whom had already come to accept the impending loss of the Earth, using the Yamato to destroy the black hole and save the world once again.
In Tengen Toppa Gurren Lagann, Guame televised his fight with Simon and broadcasted it to every underground human village as a means to demoralize them. It backfired when Simon defeated him for everyone to see and in turn, inspired humans to turn up as The Cavalry in the penultimate battle at Teppelin.
In One Piece, Doflamingo's seemingly iron-proof plan to prevent Luffy enacting his Spanner in the Works tendencies results in this. His plot involved a tournament for Ace's devil fruit, in order to distract Luffy from destroying the SMILEs factory. Sure enough, Luffy enters, and finds himself in a pickle when he can't leave the tournament without being noticed and allowing the devil fruit to fall into Burgess's hands due to being in the finals, until Sabo arrives (apparently as a Revolutionary) and trades places with him. The thing is, Sabo's appearance is largely Doflamingo's own fault. Chances are the Revolutionary Army would have never taken action on Dressrosa and Sabo would have never appeared had it not been for the tournament for the Mera Mera no Mi.
In the first story arc of Neil Gaiman's The Sandman, the villain gets hold of the amulet containing the hero's power, and during the climactic battle (which he was winning anyway) he decides to destroy it, figuring that will leave the hero powerless and easy to defeat. Instead, destroying the amulet merely releases the power, which flows back into the hero, making him more powerful than he was before...
... and then in an almost hilarious turn on events, Morpheus, the eponymous Sandman completely forgives said villain, tell him that he actually did him a favour and dismisses the pitiful, Gollum-esque creature with a pat in the back. And this for a "hero" that has been fond of Disproportionate Retribution in the past...
In the Tournament Arc of Knights of the Dinner Table, the knights get a bunch of "Doomsday" dice by rubbing their dice against the dead body of the guy who made the game. Only they end up cursing their dice, every dice in their possession and every dice of every friend they lent dice to, meaning the dice now produce the worst results possible, making just about anything a critical fumble. Everyone on the Knight's team was given this and they seemed to be in a hopeless position as they face their Smug Snake rival team... except she reveals she learn of their "advantage" and eBay'd some of the dice, believing they were blessed and very ironically leveling the playing field.
The Hulk'sraison d'etre: if you're going to kill him, at least try to make him happy about it. This makes Ultimate Nick Fury Dangerously Genre Savvy since he did JUST THAT. Pity Loki intervened.
The Onslaught saga springs to mind... "And Hulk is ANGRY!!!!"
The XXXenophile short Wish fulfillment starts with the heroine being defeated by a usurping general who declares that "henceforth you shall be my captive flower". This gives the Literal Genie who granted her three wishes before the option to grant "my captive flower" 3 wishes as well.
One of Loki's schemes against Thor (tricking him into fighting Hulk) ended up creating The Avengers. Considering that this superteam saved the world many, many times in Marvel Universe, this is THE Nice Job Fixing It, Villain for Loki...
In Sonic the Comic Sonic's Superpowered Evil Side Super Sonic was sealed in the Black Asteroid but was able to escape by charging himself up so much that he made himself into a sort of electron bomb in order to destroy the Asteroid. The explosion produced an electro-magnetic pulse that spread all over planet Mobius, which cause the totally unintentional side effect of deactivating all of Robotnik's Badniks and computers, and contributing to the end of Robotnik's dictatorship; all Super Sonic intended to was to escape the Black Asteroid.
On the subject of Sonic, Sonic the Hedgehog/Mega Man: Worlds Collide has Sonic and Mega Man attempt to use Chaos Control to fix their worlds. Mega Man's set back to normal, but Eggman's desperate attempt to win ends up messing up Mobius, turning it into a different world... as well as voiding all of his victories, restoring the Freedom Fighters to the point where they've Taken A Level In Bad Ass and giving them more allies to use in their fight. His actions also had the benefit of cancelling out, at this time, nearly all of the other villains and assorted threats in the comic, with only those from the games and American cartoons still around.
To top it off, as Eggman adapts to the new timeline he says that his new memories will overtake his old ones. It was his realization that Sonic's an embodiment of chaos that drove him to make the tech that led to the crossover and slowly tear apart the Freedom Fighters to begin with. Once his memories fully adjust, he'll become less of a threat than before.
Forever Evil: By moving the moon out of orbit, Ultraman creates havoc with Earth's oceans. The resulting flooding destroys the burial site of Black Manta's father. He's understandably a little pissed.
During the Secret Invasion arc of Runaways, the evil Skrull Chrell managed to capture every non-Skrull member of the Runaways and hold them hostage, threatening them with death unless Xavin handed over Changeling of the Young Avengers. He almost had Xavin over a barrel, but then he made Klara Prast cry. And then Klara damn near impaled him on a tree, breaking his concentration and allowing the Runaways to escape.
Transformers: More than Meets the Eye: Senator Proteus has his fellow Senator, Shockwave, lobotomized because Shockwave spoke out against him and thwarted his plan which would have killed thousands. Transformers: Robots in Disguise had Proteus believe he had broken Shockwave, but in reality, removing Shockwave's emotions and empathy just made him free to pursue his scientific experiments without any moral constraints. Shockwave no longer sees Proteus as a corrupt maniac and political rival, he merely sees him as an obstacle in the way of his goals, whereupon he calls an emergency meeting of the Senate, and the Decepticons murder all of them when they get together.
In the Vampirella story "... And be a Bride of Chaos" Lucretia, who wanted to become the Bride of Chaos and was jealous that Dracula had chosen Vampirella instead, freed Vampirella from her bonds to take over.
In one Captain America story, Cap's shield had been shattered and the shattered remains were set to be used to stop the vibranium that were following suit and heading for its anti-vibranium counterpart. Cue Klaw, who used the crises to amplify his amazing sound-based power. Destroying Cap's photonic shield, Klaw proceeds to finish off the helpless hero as Cap grabs his shattered and taped up shield out of reflex. The shield takes the brunt of the attack and, to Cap's surprise, it repaired it fully. Not only that, but it also stopped the incoming disaster. Cap, then proceeds to disperse Klaw by slinging his Mighty Shield once more and smacking him with it.
A recent What If? issue, "What If Magneto and Professor X had Formed the X-Men Together?" spun off from an old Chris Claremont story where Charles Xavier and Erik Lensherr(the future Magneto) fought against Nazi and future-Hydra founder Baron Strucker over a cache of Nazi gold. In the original story Lensherr took the gold to finance his own campaign against humanity. In the What-If, Xavier and Gabrielle Haller argued that his proposed war against humans would make him no better than the Nazis. Strucker contemptuously added, "By all means, mutant, listen to these dreamers. It will my my inevitable victory all the sweeter." Lensherr turned to Strucker and answered, "I'm glad you feel that way, Nazi. It makes my decision...easier." Strucker was later executed for war crimes, and Lensherr and Xavier became allies.
Mortality Smith captures Holmes, tortures him with an inch of his life, and gloats over the guy while he's dying. Basically, Smith unknowingly tripped off protective instincts.
The captured criminal, especially. Watson is trying to get information on his friends whereabouts, and said "If your master's actions destrory him whom I regard as the best and wisest man I have ever known, make no mistake that I shall hunt down to a man everyone who played a part in his destruction." Cue idiotic criminal most likely begging for remorse in playing a part in Holmes's long-term imprisonment, which leads to said idiot being killed IN COLD BLOOD.
In the Deva Series, the Al Hantheans were an unknown factor. Only the Yagami Academy and the Circles were unambiguously aware of the threat they posed to Earth; other nations and parties might have considered trying for non-aggression or even collusion. Then they tried to kill off Noriko and the Japanese Imperial family, hoping to take one of Earth's nations and one of Hayate's fighters out of the picture. However, the attempt did not completely succeed, and with their villainy exposed, the survivor gave a speech that will probably rally the nations of Earth into properly uniting against them. One of the higher-up villains even does some Lampshade Hanging on this.
In Light and Dark The Adventures of Dark Yagami, assuming that Dark is the hero, L does this when he shoots and kills Light, but accidentally revives him with the Life Note. Light then seeks out L for revenge, enabling Dark to trick them into killing each other.
In the Pony POV Series, Discord's Mind Rape of the Mane Cast before his downfall leads to the entire Mane Cast becoming better off than before hand, with such things happening as Applejack becoming a Living Lie Detector and Pinkie Pie becoming much more Crazy Awesome than normal by performing a Split Personality Merge and healing herself of a serious mental condition, which wouldn't have happened if he hadn't done it. Not only that, but thanks to him the Mane Cast gets twoSixth Rangers and new Elements of Harmony, one of which he made himself. The most extreme example of this happened in the backstory. Discord was the one who accidentally created the Elements of Harmony in the first place. That's right, Discord created the only thing that could defeat him.
Terra's attack on Ponyville, which served no purpose other than emotionally hurting the protagonists, ends with the Elements of Harmony — previously rendered inert by Titan — reignited, and Terra herself stripped of all power.
In the Mai-HiME fic Stain, Nao tells Shizuru that her killing her mother enabled the Reset Button that happened in the last episode to bring her out of her coma in addition to resurrecting her.
In the Lyrical Nanoha fanfic, White Devil of the Moon, some mistakes in communication lead to the Sailor Senshi coming off as suspicious to Nanoha and Fate, when they are trying to convince Nanoha to join them as their princess to fight the Dark Kingdom. When one of Beryl's lieutenants, Jadetite, attacks Nanoha's brother's wedding with an army of youma, Nanoha and Fate start believing the Senshi and then begin to work together against the Dark Kingdom.
Turnabout Storm: Because of prosecutor Trixie's ego and personal grudge against Twilight and her friends, she lets Phoenix get away with casting suspicion on Fluttershy to get more time to investigate, since she cares about making Twilight and her friends squirm more than anything. Phoenix himself points out that she could have secured a conviction and denied them a chance to gather more evidence by shutting down this line of argument.
Anthropology: After explaining his intentions to her, Discord turns Lyra back into a pony. However, this allows Lyra to use the necklace Princess Celestia gave her to return to Ponyville and gather the Elements of Harmony.
Earth and Sky: If Diamond Tiara (who runs her husband Blueblood's airship company for him) hadn't downsized her staff, leading to Pipsqueak becoming unemployed, he wouldn't have been free to become Harmony Aeronautics test pony, meaning they wouldn't be in a position to threaten the company's business.
Also, in chapter 38, Chrysalis manages to throw ponies off her trail, only to end up shooting herself in the hoof when she tries to avoid getting arrested for crimes committed by Diamond Tiara (who she was impersonating).
A Brief History of Equestria: Sullamander thought that, by killing the only general on her Joint Chiefs-of-Staff who outright opposed her, she could cow the Staff into doing whatever she wanted. Instead, the General that replaced her was Wind Whistler, who proceeded to No Sell Sullamander's nonsense and pointed out how the the Articles of Command allowed her to kill the Commander for her actions if she didn't back off. She would continue to defy Sullamander for the rest of her life, eventually launching the coup that led to both of their deaths and the rise to power of Sullamander's rival (and Wind Whistler's lover) Hurricane.
The God Empress Of Ponykind: Abaddon tries to kill the Emperor while He is still on the Golden Throne. This ends up being just what the Emperor needs to heal himself and turn the Siege of Terra against the forces of Chaos.
Miyu, by destroying Akane's child, kills the first of the SUEs, Mariko, who had the power to win over everyone she met. This proves to be a double example, as Mariko's bonding to Akane with her powers enables Kazuya to survive.
Hitomi, who starts off by mind-controlling and robbing people before moving on to mass murder, comes to Midori's attention, who contacts Mai and lets her know that she might be linked to Nao's alleged attack on Yukariko in some way. As a result, Mai and Natsuki delay going after Nao, and the group is able to cooperate against Hitomi and the other SUEs (even Nao overcomes her reluctance to associate with the other Himes by virtue of how horrific Hitomi's crimes are and out of a sense of self-preservation).
In 3 Slytherin Marauders because Lucius Malfoy insists on gloating to Arthur Weasley, Arthur's bosses assume he must be very important and well-connected and this has greatly advanced Arthur Weasley's career.
In "The Manhattan Conspiracy," Dalek Caan's decision to "study" a Time Lord's regenerative energy at work results in said Time Lord using a burst of energy against him, which saves the lives of the hybrid Daleks.
In "Every Good Fairytale," Professor Moriarty has already corruptedSherlock Holmes into his own image. The results having backfired on him, he now seeks Revenge, pure and simple... and gets it by breaking Holmes to restore his humanity. This backfires even more spectacularly, as Holmes's redemption is half of what was needed to restore Time.
In the backstory, as shown in Metamorphosis: Discord makes Celestia and Luna immortal to torture them, and lets them take the remains of the orb containing the Energy of Friendship. This gives them the time they need to become alicorns and turn the pieces into the Elements of Harmony. Longtime viewers of the show know how well that would have turned out for Discord.
During the climax of Families, Olive Branch's men manage to turn their kidnapping of Twilight, Applejack and Pinkie Pine into a complete 180 merely by telling Twilight that Spike will die.
As Luna gloatingly tells Olive Branch himself after he's arrested, his half-assed plan and the actions of himself and his lieutenants have caused the anti-Celestia movement to lose almost all support, not only allowing the royals to focus once more on searching for Chrysalis rather than defending their position, but now no one will object to Twilight officially adopting Spike.
In Guide To Recent Equestrian History, before the Reign of Discord, the ponies of Equestria are teetering on the brink of civil war. Good thing that Discord showed up to give them someone to unite against.
In Act I chapter 30, Rarosun and Surason have Dark and Rason tricked into thinking that they molested the other's respective girlfriends, and have Mizore and Kurumu restrained and are making them watch the fight. However, the two get tired of waiting and decide to morph into Mizore and Kurumu and give the boys the final push to kill each other; instead, Dark and Rason see through their disguises, promptly kill the Kiyo brothers, and subsequently realize they were duped. In short, Rarosun and Surason screwed themselves over through their own impatience and sadism.
In Act IV chapter 19, when Hitomi petrifies Moka, it allows Inner Moka to bypass her seal, break free of the petrifaction, and kick her ass.
Films — Animation
In Coraline when The Beldam tosses Coraline into the mirror for disobeying her. Of course, that's where she also left the souls of her previous victims who speak to Coraline and give her the resolve to defeat the "Other Mother".
In The Incredibles, the Omnidroid trying to rip Mr. Incredible apart actually fixes the crick in his back, getting him back in the fight.
Syndrome does this when he first meets Mr. Incredible. He has the hero captured and helpless in his "zero point energy" field. But he can't resist tossing him around and gesturing dramatically during his "I win" speech and accidentally flings him away. Although he is captured again later, it is this that allows Mr. Incredible to discover Syndrome's evil plan.
Syndrome programmed the Omnidroid to adapt to any situation. Then he arrogantly stopped during his fight with it to boast to the bystanders, giving the robot the time to figure out it was being controlled by Syndrome's bracelet. It then removed it from him, and the heroes used it to destroy the robot.
Before Syndrome, the Parr family was in a rut, trapped by monotony, dead-end jobs, and the memories of what once was. Even Bob and Helen's marriage was on the rocks. And for superheroes in general, public opinion was negative, and they had to live in hiding. After Syndrome, superheroes were allowed to operate openly once more, the public liked them again, and, most important of all, the Parrs were happy, proud, and very closely-knit, making them even better superheroes than they ever were as individuals.
Scar has Simba utterly on the ropes and is about to knock him off the edge of a cliff, when he insists on making a But Before You Die speech.... freeing Simba from the guilt he had been carrying around and giving him the heroic resolve needed to stop Scar. Doh!
Later, when trying to bargain with Simba for his life, some hyenas are about to help him. Then he goes and ruins it by trying to scapegoat the hyenas, making them back away in anger. Not only does this mean that he has to fight Simba without any backup, but it also gets him torn to ribbons by a pack of justly angry hyenas, after Simba had chosen to spare Scar's life and exile him.
In Disney's Hercules, Hades had succeeded in rendering Hercules unable to stop him from taking over the universe, not because he robbed him of his strength, but because he revealed that his Love Interest Meg was working for him, thus breaking his spirit. Then he had to go and send a cyclops to destroy him before his strength came back. By doing this, Meg went after Phil, who convinced Herc not to give up. Then the icing on the cake was that Meg got fatally injured, which broke the deal, causing the hero to get his strength back, allowing him to stop Hades.
Not to mention when Meg died, Hades offered to trade her soul in exchange for Herc's, if he could get her out of the fatal river Styx. Unfortunately, this was just the deed Herc needed to reclaim his godhood, thus allowing him to save Meg and send Hades flying into the river Styx. Major ouch.
Actually, none of this could've happened if Hades hadn't sent Meg to discover what Hercules weakness was, thus resulting in the two falling in love. The icing on the cake was that he released Meg from her Deal with the Devil with him, thus enabling her to help the good guys stop him.
Also, there was the fact that Hercules was considered a zero to everyone in Thebes and didn't have a chance at starting his path to become a true hero, until Hades started sending his monsters to kill Herc. With each monster Herc defeated, he became more famous. Man, Hades did more fixing than breaking throughout the whole movie!
Actually, when you think about it, none of this would've happened if Hades hadn't tried to kill Herc when he was a baby in the first place. Everything he did was to prevent the coming of a prophecy which said that Hercules would ruin his plans to rule the universe. However, instead of letting things play out on their own and waiting to see if Hercules would indeed grow up to be the threat he is said to be, Hades tries to get rid of him immediately, which sets off a chain of events which makes the dude exactly what Hades was afraid of. Basically, Hades had created a Self-Fulfilling Prophecy.note For how Sadly Mythtaken the movie is otherwise, this is an unexpected moment of accuracy to the source: Classical Mythology is full of prophecies coming to pass specifically because people tried to prevent them.
At the musical finale in Cats Dont Dance, Spoiled Brat Darla Dimple attempted to sabotage the performance of the animals who could threaten her career. However, each of her sabotage attempts only made the performance a bigger hit, thus ensuring the animals careers.
Then she went and screamed at the animals about the accident she caused and framed them for, thus clearing their names and resulting in her and her career literally going through the floor.
For a bit of Fridge Horror in Despicable Me, that little kid in the beginning would've died had Vector not stolen the real pyramid and replaced it with an inflatable.
Toy Story 3: The moment Lotso smashes Big Baby's locket. Cue Big Baby becoming extremely pissed and throwing Lotso into the dumpster.
In Cars 2, had Miles Axlerod not spilled oil onto the carpet, Mater wouldn't have become a spy and foiled his evil plan!
Lord Farquaad, the Big Bad of the first Shrek movie, did this on a series spanning level. He sent Shrek to rescue Fiona, which messes up his own plan by allowing Fiona to meet her true love that would break the curse and allow Donkey to meet Dragon, who helps Shrek and Donkey stop his wedding and eats Farquaad. In the second movie, Prince Charming's goal to rescue Fiona and thus Fairy Godmother's intention to rule Far Far Away through him are foiled because Farquaad sent Shrek to rescue her already. Most importantly, it foiled Rumpelstitskin's attempt to get Fiona's parents to sign a Deal with the Devil with him, letting him erase them from existence and conquer Far Far Away because Shrek rescued Fiona and rendered the deal pointless. Even further back, the only reason Shrek interfered at all in any of this was because Farquaad's deporting all the fairy tale creatures to his swamp ticked him off. Really Nice Job Fixing It, Villain!
In Frozen Hans tries to kill Elsa, and Anna throws herself in front of the sword before the curse freezes her solid (and shatters the sword in mid-strike). Because Anna did that to save Elsa, it was an act of true love that would break her curse, something she might not have been able to do had Hans not given her the opportunity.
Films — Live-Action
Star Wars: Luke is struggling with the dark side in Return of the Jedi, but the Emperor's constant taunting keeps Luke from going over. Not only that, when the Emperor decided to forgo turning him and instead try to kill him, he ended up getting the exact opposite: instead of Luke turning to the Dark, Vader turned back to the Light in order to protect his son. Even Irregular Webcomic! spoofed this, with Vader complaining he could get Luke to turn if the Emperor would just stop butting in.
Superman II: In an overlap with Batman Gambit, Supes confides in Lex a means to Depower the escaped Kryptonians and save Earth. Something that is in Luthor's interests since they've repeatedly shown they care nothing for him or honoring their deals. Of course, Lex betrays Supes and tells them the plan... but instead, he's actually been tricked by Superman and helped him depower them! It seems Lex is so predictably evil, Supes could count on him always being his own Starscream.
UHF: In an earlier scene, R.J. Fletcher gives a penny to a panhandler, who thanks him sincerely. It turns out that the penny was extremely rare and valuable, so the panhandler was able to sell it for enough money to buy several shares in the station Fletcher was trying to close down.
In Kung Fu Hustle, the protagonist, Sing, is rewarded for his Heel-Face Turn... by getting his face beaten into a pulp by The Beast. This however, clears up his chi flow, turning him into a true Kung Fu master, and he soundly defeats the Axe Gang and The Beast.
Ghost Rider is unable to use his penance stare on Blackheart because Blackheart doesn't have a soul. Then Blackheart absorbs a thousand damned souls into himself. The Rider proceeds to render him catatonic.
Ghost Rider: "A thousand souls to burn! Look into my eyes!"
Marty and George's plan to make Lorraine fall for George goes awry when Biff shows up and tries to have his way with Lorraine. Although intimidated, George stands his ground against Biff. He tries to throw a punch, but Biff intercepts it, then begins twisting his arm. Lorraine tries to intervene, but Biff forcefully pushes her aside. After he does so, he laughs. This gives George the resolve he needs to punch Biff out and later, win Lorraine's heart.
Marty's original plan- pretending to have his way with Lorraine, only for George to jump in and play Superman - was failing hard because Lorraine wanted to jump him. Biff's intervention unwittingly set things back on course.
Not only did Biff end up repairing the status quo, but he ended up completely reshaping his own future. George goes from weak-willed pushover constantly being taken advantage of by Biff, to a confident and successful author. Biff, meanwhile, waxes George's car.
Biff was drunk out of his head and not capable of making any kind of coherent plan. This is sufficiently established by him doing this in the first place - if not for George turning up, he could very well have ended up in prison for a long time.
In the live-action Popeye movie, the eponymous sailor-man hates spinach, so Bluto force feeds him an entire can, just to be mean. You can probably guess what happens next.
In Ben Hur, The titular character taunts the man who sold him into slavery with this.
Messala: By what magic do you bear the name of a Consul of Rome?
Judah: You were the magician, Messala. When my ship was sunk, I saved the Consul's life.
Highlander II: The Quickening: General Katana, for no good reason, sends his mooks to try and kill Connor MacLeod decades after he becomes mortal because he's worried Connor would return to try and kill him. During the altercation with the mooks, Connor beheads one of them and as a result, regains his immortality, and becomes young again, and then is later able to take out the shield that is causing harm to the planet.
The Terminator: John Connor has just defeated Skynet in the humans vs. machines war. Skynet sends a Terminator back in time to kil his mother, to eliminate the problem before it can even become a problem. In response, the resistance sends back Kyle Reese, who gets Sarah pregnant with John and creates a Stable Time Loop. If Skynet had never sent back the Terminator in the first timeline, John would not exist and Skynet might very well have won.
Mr. Deeds Goes to Town features this trope at the climax. Deeds is lethargic and disinterested in his own defense because of the constant betrayals he's suffered throughout the film, including from Love Interest reporter Babe. When it looks like he's finished, Babe desperately takes the stand to offer up the defense he won't. The prosecutor, frustrated by her emotional pleas, requests that he be allowed to treat her as a hostile witness since "she's obviously in love with the defendant". This breaks Deeds out of his depressed stupor, and the next time he's prompted to speak in his own defense, he does so- and lays out an epic verbal smackdown on the prosecutor's entire argument.
In Face/Off, Castor Troy has a bit of a Pet the Dog moment when he saves Archer's daughter from being assaulted and gives her a butterfly knife so she can defend herself against future attackers. She uses it on Castor himself at the end of the film.
In the sequel, his wife, Lady Benzene, has Zearth's spirit crushed after her robotic copy, Ultraman Shadow defeats him with ease, making him unwilling to transform. Then, she has to go call him out to try and stop her so she can destroy him. Her taunting causes Zearth to train, take another level in badass, and overpower Shadow. Then, she goes and broadcasts the fight around the world to try to crush humanity's spirit, this backfires when Shadow finally has the upperhand, the people of Earth all chant Zearth's name, giving him to strength to destroy Shadow once and for all.
In Cliffhanger, while hero Gabe is retrieving the first briefcase of money for the thieves, Big Bad Qualen remarks that they don't need two guides and instructs his crew to kill Gabe when he comes down. Of course, he says this while standing next to Gabe's partner Hal, so Hal naturally yells to Gabe not to come back down, allowing Gabe to flee and become the fly-in-the-ointment to Qualen and crew. Had Qualen kept his mouth shut until Gabe came down, or instructed his men out of earshot, he would've saved himself a lot of trouble.
During the scene with the Oracle in The Matrix, she explains that Neo technically isn't the One, but he will probably be one in a later life. Later in the film, Agent Smith kills Neo. However, Trinity manages to revive him and Neo awakens as the One. Nice job fixing it, Smith.
In The Matrix Revolutions, Smith copies himself over Neo in their final battle. Since Neo is connected to Deus Ex Machina, Smith is promptly deleted.
In The French Connection, narcotics cop Jimmy "Popeye" Doyle is tenaciously chasing down a major heroin deal. At one point, with one officer dead and little in the way of results, his superiors order him back to his regular work and close the case, effectively leaving the deal to go ahead as planned. Unaware of this, and concerned that heï¿½s giving their US clients cold feet, the French traffickers authorize a hit on him. The hit goes badly wrong and Doyle runs the hitman down. He gets the case re-opened on the strength of that, ultimately intercepting the heroin and most of the traffickers.
When Bruce Wayne goes to confront mob boss Carmine Falcone at his favorite hangout, Falcone gives him a "The Reason You Suck" Speech. It's intended to break his will, but Bruce actually agrees with everything Falcone says about him. He immediately leaves the restaurant and embarks upon his journey to become Batman.
Ra's Al Ghul deciding to crash Bruce's birthday party for a little Evil Gloating and attempting to kill him. It's likely that if he hadn't done this, Bruce would have never figured out Ra's plan at all, and definitely not in time to actually stop it.
If Loki hadn't ruined Thor's big day and incidentally gotten Thor banished, Thor wouldn't have learned humility and would have remained the same reckless and arrogant god that he was, instead of maturing like he did. In fact, Loki visiting Thor in his cell was what changed Thor into a better man.
Again near the end of the movie. Loki was in charge, Thor was trapped on Earth and mortal. But Loki had to send the Destroyer to finish Thor. That gave Thor the chance to make the Heroic Sacrifice that restores his powers.
During the fight on the Bifrost Loki has the edge, since he's quite willing to do what it takes to win while Thor is hesitant to fight him. And then Loki makes a purely gratuitous threat against Jane Foster...
Loki does it again. After so carefully sowing the seeds of dissent among the already volatile heroes, he takes out Agent Coulson, literally giving them something to avenge, which brings them together as a team.
The portal he opened to bring his alien army to Earth also conveniently gave Iron Man somewhere to dump the nuke aimed at Manhattan, which also destroyed Loki's army.
In Kung Fu Panda, Lord Shen attempting genocide on the pandas not only enabled Po to complete the prophecy, but also provided the Valley of Peace with a way to stop Tai Lung in the original film.
The Devil in the Scare 'Em Straight flick Escape from Hell, when the protagonist Eric arrives after inducing a near-death experience. Rather than attack him outright, the devil just tells him exactly who has gone to hell and why, and that his recently converted father didn't go there. He only attacks him just as Eric is brought back to life, then chases him into a church for good measure in case Eric needed any more help converting to Christianity. The Devil Is a Loser indeed.
In the film Immortals, the villain is on the verge of victory, and possesses a magical Energy Bow that can fire infinite shots, which destroy men and rocky walls alike. So when it comes time for the final battle, he fires said bow exactly one time at the giant wall the Greek soldiers are hiding behind. Which creates exactly one small opening for his massive army to use, giving the Greeks plenty of time to defend such a small area.
Viktor's decision to kill his only daughter for loving a Lycan kicks off the war between vampires and werewolves that leads to the death of Vampire Elder Amelia. Not only that, his decision to spare Seline because of her striking resemblance to the daughter leads to the death of him and Markus, also Elders. Without any strong leadership, the vampire covens fall apart and become fairly easy pickings for the Lycans by the events of Underworld: Awakening.
Considering that his fear of a vampire-lycan hybrid was a primary motivation for his actions, his initial refusal to believe Seline ultimately results in the (re)creation of Michael as a vampire-lycan hybrid; his murder of Singh leads to his rival Markus being reawakened and becoming a hybrid.
In Diamonds Are Forever, Shady Tree discovers just in time that the diamonds were fake and got James Bond out of the retort Wint and Kidd had put him in. Bond takes the opportunity to casually stroll out of Slumber, Inc. during the inevitable questioning and later figures out that someone's bumping off the diamond smugglers when Tree gets shot later on.
Shady Tree: [after the casket is out of the retort] You dirty double-crossing limey fink, those Goddam diamonds are phonies! James Bond: Now don't tell me... you're St. Peter? Shady Tree: Paste! Glass! Where's the real stuff, Franks? James Bond: Where's the real money? Morton Slumber: What do you mean? James Bond: You wouldn't burn up 50,000 real dollars, now, would you? Shady Tree: One last break, Franks. Where are the real diamonds? James Bond: You get me the real money... [climbs out of the casket] and I'll bring you the real diamonds. Shady Tree: Where the hell do you think you're going? James Bond: I hear that the Hotel Tropicana's quite comfortable. My condolences, gentlemen! [Morton Slumber slams the now-empty casket shut as James Bond leaves]
Venom/Eddie Brock, in Spider-Man 3 does this in a more drawn out sense. After the symbiote bonds with him and he gains all of Parker's memories, you'd think maybe he'd catch Peter unawares, or at the very least if he wanted an ally, go to Harry Osbourn, who was still hating Peter at that time. But no, first he recruits Sandman and then he kidnaps Mary Jane. Which leads to Harry's Heel-Face Turn, Big Damn Hero moment, and the Heroic Sacrifice that saves Peter and results in Brock's demise.
If Talia had just kept her mouth shut about flooding the fusion reactor basement to the heroes, they would have continued to waste time dragging the reactor to the location to attempt to reconnect it, which would not allow Batman to Relocate The Explosion in time.
Bane releases all of the Gotham City's incarcerated, including Selina Kyle/Catwoman, who manages to unceremoniously blow him away in time to stop him from killing Batman at the film's climax, leading the above-mentioned Fix-It moment.
Bane's calling out of Commissioner Gordon's cover-up leads to Batman once again being looked upon as a hero and a symbol of hope for Gotham city. His plans for anarchy unravel from that point on.
In Iron Man 2 Justin Hammer's deal with Ivan Vanko turns out to be a mistake from his perspective. Vanko proves impossible to work with, uses Hammer's resources and technology for his own single-minded vendetta, ruins Hammer's Expo showing (while placing thousands of people in immediate danger, we might add) and ultimately leads to Hammer's arrest when it's discovered that he's behind Vanko's escape. The real kick in the pants? It was all totally unnecessary. If Hammer had simply waited, Tony Stark would have self-destructed completely on his own, been discredited in the eyes of the public, probably died from palladium poisoning, and Hammer would have still gotten his hands on the War Machine armor and been allowed to study/weaponize it as the premier US military contractor.
Man of Steel: Zod's decision to also take Lois hostage for additional leverage and information and to hold her in a room that has a console. The console has a slot for the spaceship key that Clark slipped her so they wouldn't find it on him, and inserting it allows Jor El's Virtual Ghost to upload to the ship, help Lois and Clark escape, and give them crucial information.
In the musical 1776, Judge Wilson (who is against independence) mentions the they must first "define the nature of the beast," later, when it looks like the move might be defeated, Adams and Franklin use this as the means to delay the vote until they write The Declaration.
Little Giants: If not for Spike hitting Junior, Becky wouldn't have returned to the Giants.
In Airheads, SWAT team leader Carl Mace reveals to everyone that Chazz Darvey used to be a huge geek named Chester when he was in high school, in an attempt to make people less supportive of him. Instead, it makes everyone more supportive of him, as they reveal their own geeky pasts.
Elysium: The plot to open up Elysium to everybody on Earth is only possible because of Delacourt's desire to overthrow the current government, requiring a virus that can reboot the system. Then Max gets a hold of it...
In Super Mario Bros., King Koopa gets bitten in the tail by everything he ends up de-evolving. The de-evolved Toad is the reason the Goombas, his entire army, become incapacitated, and the second his two cousins are evolved to become smarter they realize it sucks working for him and they immediately turn on him. And of course the fungus which is actually the de-evolved king does everything in it's power to hold him back every step of the way.
Mayor Augustus in How the Grinch Stole Christmas! not only wrecks his own materialistic drive on Whoville, but also leads to the Grinch's Heel-Face Turn. He ends up doing this when he decides to humiliate Cindy Lou Who for her decision to bring the Grinch into the town's celebrations the night before, which lead to the Grinch's theivery because of his own asshole-ish decision to humiliate the Grinch there. By humiliating Cindy Lou, her father, Lou Lou, stands up for her and realizes that Christmas isn't about the gifts, but about family. When the Grinch goes to listen for the sounds of sorrow and ends up getting singing, this ends up leading him to realize the same thing.
In the 1985 Brewsters Millions, Brewster would have failed to meet the conditions of his full inheritance if the junior partner of the crooked law firm that stood to profit from the failure had just kept his mouth shut for half an hour.
In the first live action Astérix movie, Asterix & Obelix Take On Caesar, Asterix and Obelix infiltrate a roman camp to free Panoramix, with Obelix having to pretend to be a roman legionary until Asterix gives him a signal to stop acting. Unfortunately, the two get seperated with Obelix becomming Detritus' right hand man and Asterix being sentenced to die in an arena filled with wild animals, unable to give Obelix the signal since he is out of hearing range. And then Detritus unknowingly helps Asterix give Obelix the signal because he is curious what exactly Asterix is shouting to Obelix and uses his skills of lip reading to find out.
Before RIFT's attack, all the AI research teams were working independently and were probably decades away from a true AI breakthrough; Max flat out admits that a thinking machine is essentially a pipe dream and that their progress toward that goal is more productive in its incidental advances in other scientific fields. After the attack, key research ends up being transferred to the Casters at the same time Will is told he will die in a matter of weeks, giving them both the necessary research and the motivation to apply it. Thus, RIFT's actions create the very AI they sought to prevent. If they had done nothing, the research would still exist, but it would be very unlikely that human trials would be put into play any time soon, nor would it be likely these independent teams would share data, since Will specifically notes that he's never taken defense contract cash (which is where the research comes from).
This also plays out later in the film. After Will's upload and relocation to Brightwood, he had kept to himself, working on peaceful advances in technology that were completely benign. Bree has fliers distributed accusing the Brightwood Data Center of human experimentation, which was a complete lie, and not long after that two guys mug Martin and beat him nearly to death. Will uses his nanomachines to save Martin's life, in the process upgrading him into a networked superhuman, again kickstarting the very thing RIFT sought to stop. It did succeed in getting their cause greater recognition, though, so, by accident if nothing else, it wasn't a total backfire.
In Need for Speed, the antagonist Dino made a critical mistake of not getting rid of the red Koenigsegg which he previously drove that killed Pete, enabling Tobey not only able to use it for the De Leon race, but it is also the critical evidence Tobey needed to clear his name of Pete's death.
This is Spenser and Baldwin Furnshill's chief method to solving crimes without evidence. Annoy people until they try to kill you, then find out who they worked for. Though Baldwin doesn't actually try to annoy people; usually the bad guy who falls into this trap hates him for his rank and title, or his loyalties and suspected beliefs, said series taking place in a particularly hectic time of English history. Spenser, on the other hand, is actively trying to invite this trope a lot of the time. A lot of his cases would have been a lot shorter (and unsolved) if the villains had been smart enough to just shut up and leave him alone.
The Draka: after the Final War nearly destroys the eco-system the Draka respond by invoking strict environmental standards to ensure stablity. Nature preserves are created from entire continents and the population levels are kept low.
The Swallows and Amazons book Great Northern? has a textbook example of this. The protagonists, while sailing through the Hebrides, encounter what they're pretty sure is a rare bird, but have to leave before they can verify it, and accidentally let its existence — but not location — slip to an egg-collector, Mr. Jemmerling. Captain Flint, their designated adult supervision, is going to make them leave before they can go back, leaving Jemmerling free rein to find the birds. Instead, Jemmerling tries to convince and then bribe Captain Flint to tell him where the birds are, and succeeds only in convincing him that they're worth going back to find.
In the Dale Brown novel Plan of Attack, the Russians conduct nuclear sneak attacks on the US, supposedly to create nuclear parity. Our Military Maverick protagonist Patrick McLanahan for once obeys an explicit order of the POTUS to hold on a retaliatory strike against the Russians. When the Russians prove their continued hostile intentions by attempting a nuclear bombing of the base Pat had forward-deployed to, one that had no nuclear weapons, it shows them for the liars they are and gives him a casus belli.
In the Andrew Vachss Burke book Terminal, one character describes how gangs putting out hits on suspected rats leads to cons ratting out for real.
In Harry Turtledove's The Guns of the South, Afrikaaners use Time Travel to help the Confederates win theAmerican Civil War, hoping to build a strong white supremacist nation that they can ally with in the future. Though their plans are impeded by Robert E. Lee, who wins the presidency of the Confederacy on a platform of gradual slave emancipation, there are still enough Pro-Slavery Confederate citizens and congressmen to defeat any sort of government action to actually end slavery, and there is even talk amongst some states of seceding from the Confederacy and starting their own nation (again) to preserve slavery indefinitely. However, the AWB then launches an assassination attempt against Lee on his inauguration day, which slaughters dozens of civilians and many ranking members of the government, which unites the entire country behind Lee and gives him the political clout to ram through his gradual emancipation bill.
In A Crown of Swords, Moghedien freaks out upon catching sight of Nynaeve in Ebou Dar and loses character long enough to balefire the boat she had just gotten on. At that moment Moridin strokes her Soul Jar, causing her to involuntarily convulse and miss Nynaeve and only sink the boat. Nynaeve is trapped in the rapidly sinking wreckage ï¿½ at which point the resulting despair causes her to permanently break free of the mental block that had been preventing her from channeling at-will since the beginning of the series.
Harry Potter, in chronological order, starting with book four:
In Harry Potter and the Goblet of FireThe Mole, in order to surreptitiously abduct Harry from the school, plants him into the Triwizard Tournament and then oversees his victory by giving hints. One of those hints drives Harry to master a specific spell that he otherwise failed at, and then he uses this spell to escape from Voldemort in the finale.
Even better, in the interest of presumably staying in character while impersonating Mad-Eye Moody, he insists that Harry is able to completelyresist the Imperius curse after he witnesses him doing so better than his classmates. Guess what he also does successfully in the aforementioned finale.
In Harry Potter and the Deathly Hallows the heroes spend most of the story in vain searches for the Big Bad's Soul Jars. At one point they are captured by the villains and, long story short, one of the villains suspects that they might've sneaked into her bank vault. She freaks out so much that that her dreadful master might find out about it, and spends so much effort torturing the heroes just to find out whether they did or did not, it gives Harry an inspiration for a leap of logic, and he correctly deduces that the Soul Jar must be in the vault.
And in general, his decree that no one was to kill Harry. Thus his minions' hands were basically tied when dealing with Harry, even though he and his friends would frequently run into those minions.
The original Count Dracula forced Mina Harker to drink his blood to form a Psychic Link between them that he could use for Mind Control and to spy on the rest of the heroes through her so he could see whatever they were planning against him next. Unfortunately for him, the link worked both ways, allowing Mina to warn the others when he was coming their way and figure out where he was hiding or heading during the climactic Stern Chase. He gives the heroes a ticket to his mind that he can't revoke even when he eventually tries to do so.
Ironically, many later versions of this story have picked up the weird trope that Mina and Dracula had some kind of love between them; in the original Mina loathed the monster and was probably second only to van Helsing in importance in bringing about his downfall.
A minor version in Lin Carter's The Quest of Kadji: the Big Bad has captured one of the two young people who've independently sworn to destroy him, and taunts her that her sweetheart won't be able to act while she's his hostage. She gloomily says the boy is not in love with her. The villain can't resist sneering that, just like her, young Kadji is under a "no-fooling-around-until-you've-killed-the-bad-guy" vow, which is the only reason neither has made serious advances to the other. Yes, in an attempt to mock her, the villain has actually raised the girl's morale.
In Starfire by Charles Sheffield the detective protagonist figures out the murderer's identity, but has no proof. He draws the murderer out into open by announcing he found a supposedly missing victim, and where he stored the corpse. The villain can't help but go check on the body, where confronted by detective. Even then the villain could have saved the situation by simply feigning ignorance and leaving. With security cameras on, detective could not exactly initiate violence. Villain solves his problem by drawing weapon first — on camera. Detective is a much faster shot. Nice going!
In Lois McMaster Bujold's Vorkosigan Saga book Falling Free, the heroes at one point want to rescue someone from the villain. Since they're in outer space, they need the help of a spaceship pilot, and the only one they've got is not one of the heroes; he's helping them for pay, and is unwilling to risk himself on some harebrained rescue scheme. One nasty phone call from the villain later, and he's on the heroes' side. This is not the last time someone helps the heroes due to the villain's Jerk Ass tendencies.
Another Lois McMaster Bujold example: in The Curse Of Chalion, Chancellor dy Jironal stabs and kills the protagonist, dy Cazaril. His death allows the Lady of Spring to undo the curse and fix the realm.
Vicar Zahspahr Clyntahn's actions throughout the Safehold series tend to do as much as help the Empire of Charis as it does to hurt it. A specific example occurs in How Firm a Foundation. The island Empire of Charis needs an ally in the mainland, the Republic of Siddarmark would be perfect, but they're right next to the Temple Lands, which are content to leave them be, and even let them get away with ignoring a Church-imposed trade embargo against Charis, so long as they don't act outright against the Temple Lands. Cue Clyntahn going behind his fellow Church Leaders' backs creating riots in Siddarmark forcing them to go independent and opening the door for Charis and Siddarmark to ally at the earliest opportunity.
An earlier example would be his assassination of Prince Hektor and his eldest son in By Heresies Distressed. Cayleb of Charis had spent the entire book conquering Hektor's princedom of Corisande with the knowledge that any surrender Hektor offered would only last until Hektor could backstab him. Clyntahn, knowing Hektor may be forced to surrender, left orders to have him killed and Cayleb blamed for the attack in that event. This succeeds and makes Charis' occupation of Corisande very difficult in the short term. In the long term, people realize that Clyntahn is a more likely suspect. More importantly, Hektor's surviving children realize this, seek asylum in Charis, befriend Cayleb and Sharleyan, and pledge Corisande to Charis' cause. Clyntahn's actions made Cayleb's job more difficult as intended, but ultimately replaced a ruler who would've betrayed Cayleb with rulers who were loyal to him.
In Gösta Knutsson's Peter No Tail, the atagonist, Måns, usually schemes for Peter to get in some kind of trouble, but either Måns or his helpers, Bill and Bull, screw it up most of the time, and not seldom, putting Måns in the trouble instead of Peter.
Saruman ordering his Uruk-hai to take Merry and Pippin to Isengard, instead of Mordor as the Morgul orcs wanted:
Practically saved the entire quest. If Merry and Pippin were taken to Mordor there would have been no chance of rescue on the way, and Sauron would have soon found out that Frodo and Sam were heading straight for him with the Ring. They would have been intercepted, and Sauron would have retrieved the Ring. Instead, on the way to Isengard the Rohirrim unknowingly saved Merry and Pippin, and Sauron didn't find out about the 'destroy the Ring' quest until it was too late.
Bites Saruman in the backside in a more personal way, too. Taking them towards Isengard meant Merry and Pippin ended up in Fangorn Forest, met up with Treebeard and helped convince him and the Ents to join the war against Saruman, resulting in the Huorns wiping out Saruman's armies at Helm's Deep and the Ents themselves storming and capturing Isengard, effectively ending Saruman's involvement in the War of the Ring.
In chasing after Merry and Pippin, Aragorn, Legolas and Gimli were able to meet up with Gandalf again, lift Théoden from his despair and help Rohan's forces to fend off Saruman's armies, which in turn meant Rohan was in a much better condition of answer when Gondor called for aid...
In another example; Sauron creates a thick cloud of smoke to block out the sun during the assault on Minas Tirath. This proves to be an excellent cover for Théoden and the Rohirrim to attack his forces.
Sauron does this before the main plot proper even starts; he captures Gollum, tortures him for information about the being that stole the Ring from him and where they came from...and then lets Gollum go. Meaning that, with Gollum guiding them, Frodo and Sam were eventually able to get into Mordor more or less undetected - albeit with some nasty encounters with spiders and orcs along the way - and, when Frodo was unable to destroy the Ring and claimed it for his own, Gollum unintentionally brought about the Ring's destruction when he bit off Frodo's finger to get it.
In Pride and Prejudice, Lady Catherine is so affronted by the idea of Mr. Darcy marrying Elizabeth Bennet that she confronts Elizabeth and tries to extract a promise from her not to accept Darcy's proposal; when Elizabeth refuses to promise any such thing, Lady Catherine has a similar confrontation with Mr. Darcy... which gives him reason to hope that he still has a chance with Elizabeth even though she rejected his previous proposal in very emphatic terms. Had Lady Catherine not seen fit to get involved, each of them could have gone on indefinitely believing that any chance they had with the other was long gone.
In The Night of Wishes, an evil sorceror and his witch aunt brew a potion on New Year's Eve which grants the opposite of any wish spoken aloud after a drink, gleefully intending to make a grant show of fixing the world in front of their unassuming pets, while actually wreaking havok. Only those are onto them, find a loophole in the spell, and with a little outside supernatural help manage to destroy the reversing part of the potion without the villains noticing. The world's people are not gonna believe how much luck and prosperity they are going to have next year.
As a meta-example, Mephistopheles in Goethe's Faust proclaims that he is "Part of that Power which would The Evil ever do, and ever does the Good."
At the climax of Flinx in Flux, the Animal Wrongs Group that has been hunting Flinx down in order to "make him normal" shows up just in time to accidentally rescue him from the Big Bad who wishes to experiment upon him instead. As a double example, Flinx finds that the sedation method that the Big Bad used on him has also woken a new form of his empathic powers, which he subsequently uses to defeat both groups of antagonists.
In The Norwood Builder, the titular villain fakes his own death and frames the son of his enemy, fabricating a perfect set of clues that managed to fool even Holmes. Later, he decides to add one ultimate clue in form of a bloody fingerprint on a wall... after Holmes has already scanned every inch of the house, which leads to discovery of villain's hideout.
In Percy Jackson and the Olympians, the Big Bad, Kronos plans on overthrowing the gods, but needs a mortal host in order to escape Tartarus and eventually come back completely. He uses the fact that gods tend to ignore their children against them, finding someone with a grudge against the gods and using him as his host. Only problem is the person he picks has enough willpower to overcome Kronos' influence when Kronos attacks the girl he has a crush on. He ends up killing himself, taking Kronos down with him and scattering the Titan to dust. Not to mention that as a result, the gods promised to claim all their children, making the training camp for demigods even stronger then it was before. Good job bad guy.
In Tanya Huff's Smoke and Shadows, the Shadowlord, an evil wizard from another world sends shadow minions, and later comes to Earth himself, in search of a wizard who escaped during his conquest of their world. He feared they would return to overthrow him. Ironically, the wizard in question was a bit of a coward and had no intention of ever going back or fighting the Shadowlord. Only the fact that they are now being actively pursued motivates them to take a stand.
Zigzagged in Luke Skywalker and the Shadows of Mindor. Lord Shadowspawn claims that Luke is the rightful heir to the Empire and plans to put him in that position; his top officers, the notable one being one Captain Klick, are old Jango Fett clones and therefore particularly obedient. Shadowspawn is actually a character, the man behind the curtain being Blackhole, an actual villain who also wants to take over Luke's body and identity. When his initial attempt to do so fails, he orders Klick and his men not to let anybody out of the place in question ï¿½ only for Klick to kneel to Emperor Skywalker instead. However, Luke does not abuse his new position as much as one might expect, and Blackhole realizes at the same time that Leia's body would be even better. Late in the novel, when all Hell breaks loose, Luke finally promotes Klick to Air Marshal and, through him, has the Imperials work with the Republic forces. To his horror, Blackhole is able to control their mind and makes them run amok.
Near the end of Les Misérables, Thenardier tries to blackmail Marius with the knowledge that his father-in-law Jean Valjean is a criminal. He produces an item (a scrap of cloth taken from a coat in the book, a ring in the musical) which he claims came from the body of a murder victim that Valjean was carrying through the sewers... which proves that the "dead body" was Marius himself and that Valjean saved him from certain death at the barricade. The knowledge enables Marius and Cosette to reconcile with Valjean shortly before the latter's death.
In Protector of the Small, Joren tries to sabotage Kel by giving her weighted training lances. However, Kel soon starts using all weighted weapons for the same reasons pages and squires intentionally do—they help to build up strength and endurance, and using weighted weapons on top of the exercises she started when she failed with the lance quickly removes any disparity between her and the boys. When she does get a regular lance later on, it actually throws her off because she's so used to the weighted ones. This explanation for her bad performance quite impresses Lord Wyldon—another thing Joren did not want happening.
From Honor Harrington, a cataclysmic attack by the Big Bad on the Manticoran home system ends up breaking five years of diplomatic gridlock between Manticore and Haven by spurring President Eloise Pritchart of the Republic of Haven to take a good chunk of her Cabinet and sail straight to Manticore itself, whereupon she sits down at the table with Queen Elizabeth III, clears up roughly a decade of diplomatic misunderstanding between them, offers a peace treaty, and then proposes a military alliance. Elizabeth takes her up on it. Awesome ensues for Tom Theisman and Honor Harrington (who get to team up on the command deck), Sonja Hemphill and Shannon Foraker (who head out to Haven's technological playground and get busy), the Manticoran and Havenite navies (who get to take the results of their Lensman Arms Race and go play), and Elizabeth and Eloise themselves (who get to mastermind it all) — but not for the Big Bad, who is oh so very screwed in an infinite variety of ways. And heknows it.
The entire Kamen Rider series STARTED because of this trope:
To elaborate: Shocker kidnaps a motorcycle racer/biochemistry student and turn him into a grasshopper-themed cyborg, who escapes before he can be brainwashed to serve them, and fights against them as Kamen Rider.
They try to create another, more powerful Rider to destroy him, but gets freed by the original Rider, thus doubling Shocker's chances of complete and utter failure!
Kamen Rider Black: If this tv special introducing the show is to be believed, Kotaro couldn't even transform until he was electrocuted and roughed up by Gorgom priests. Kamen Rider Black Rx is another example, as Crisis damaged Kotaro's Kingstone and threw him into space, restoring and enhancing his powers.
The Librarians, the Serpent Brotherhood locks Cassandra(a traitor to the protagonists) in a cell after she helps them begin the process of bringing magic back to the world. She is then discovered by the aforementioned protagonists, and plays an essential role in stopping the Serpent Brotherhood.
In VR Troopers, Grimlord does this with Dream Master, growing impatient at how long it was taking him to defeat Ryan Steele. At this point, Dream Master had weakened Ryan with mind games about his father and he had connected him to an electrocution chain. Had the gunbots and tankbots not interfered, Dream Master would have beaten Ryan Steele, since JB was occupied with another monster and Kaitlin was too weakened by Dream Master's nightmares. But after the gunbots interfered and the two of them escaped fire, Dream Master continued with his shock chain only for Ryan to find a chain in this new location to redirect the current before delivering a beatdown on what was supposed to be a Monster of the Week.
Similarly, different times, a Monster of the Week has a trooper on the ropes, then the air force comes in for a distraction, apparently hitting both the monster and the trooper, giving the Trooper time to think of a new battle plan while bazookaing down the airforce.
Another time, Arachnobot nearly had the Troopers beaten, but Doom Master himself killed Arachnobot out of jealousy. Thanksfully for his sake, he thought it was the Trooper that did it, not Doom Master.
At the end of Angel's "permanent midnight" mini-arc, Angelus, being Chaotic Evil and all, decides to double-cross the Lawful Evil villain who'd blotted out the Sun over Los Angeles. The Beast is nigh unvulnerable, until Angelus uses a bone dagger made from its body to kill it. Unfortunately, as foreshadowed by a mystical dream Angel had earlier, that undoes the spell and brings the Sun back. Hundreds of rampaging vampires die instantly, and Angelus is sent scrambling for the nearest safe shadow.
Angelus: Aw crap! You mean killing the Beast really does bring back the Sun? I thought that was Angel's retarded fantasy!
Then there's the series finale, where Hamilton, newly favored by the Senior Partners of Wolfram & Hart, beats the crap out of Angel... until his boasting reveals the source of his power, to a vampire.
Hamilton: Let me make this as clear as I can. You cannot defeat me. I am part of them, the Wolf, the Ram, and the Hart. Their strength flows through my veins! My blood is filled with their ancient power!
Angel: (grins and pops his fangs) Can you pick out the one word there you probably shouldn't have said?
In the special "The End of Time", things look bleak indeed. The Doctor has just crashed through the skylight of the Naismiths' mansion and is badly hurt, Rassilon and the Time Lords have escaped the Time Lock with the Master's help and plan to end time itself so they can Ascend to a Higher Plane of Existence. They practically had victory in the bag, but Rassilon, the Lord President of the Time Lords, tells the Master he's outlived his usefulness. Not what you want to tell the Master, who isn't quite sane at the best of times and has just won the Superpower Lottery. Then Rassilon lets slip that he is responsible for the drumbeat that the Master's heard all his life and that has driven him steadily more crazy. The Master tells the Doctor to "get out of the way" and uses his life force to electrocute Rassilon, protecting the Doctor from him until they all disappeared back to the Time War.]]
Again in the Weeping Angels two-parter. The army of Weeping Angels are low on power from being stuck in the catacombs for eons, so they start draining power from the crashed ship they're currently on, the Byzantium, in order to survive. This has the side-effect of deactivating the ship's artificial gravity, causing the unprepared Angels to fall into the crack in time and be erased from existence.
In "The Day of the Doctor", a Zygon gets too into character impersonating Kate Lethbridge-Stewart, and forgets that when you're The Mole you're supposed to stop pretending to be on your enemy's side before giving them everything they need to stop you.
Gossip Girl has Blair, who seems to create this and Nice Job Breaking It, Hero in other people (depending on whether she's the good guy at that point or one of the bad ones). Chuck gets her latest boyfriend's mother to come break them up? In one party Blair gets her approval. Chuck tries to seduce her only to be caught by said boyfriend? Blair finally gets laid by new boyfriend. Jenny tries to beat Blair and become Queen B? Within a few weeks, she's back and dangerous. Vanessa tries to blackmail Blair? Humiliated by episode's end. Vanessa tries to break up her and Nate? They're closer than ever by episode's end. And most of this is just the first two seasons! She's still going - at the end of Season 4 Serena's attempt to hurt her actually leads to her relationship with the prince becoming public, her being approved by his mother, and finally her getting engaged to him. Lampshaded by Dan - "Only Chuck and Blair could go to war and end up happier than when they started." Also, his attempt to attack them that episode? Ended up with Chuck and Blair having fantastic sex on a piano. Let's face it, no one can hurt Blair without helping her.
Dollhouse: Alpha's entire goal in "Briar Rose" and "Omega" was to turn Echo into a composite like himself. Composite!Echo's first act was to hit Alpha with a pipe.
Justified in that, since he was a doll, most of his personalities are hopelessly lovelorn romantic rape-slaves specifically designed to put their assigned sexual interest on an absurdly high pedestal, and many of them were tailored to work with Echo specifically. Not all that many of the fractured components of his personality were dispassionate, experts in psychology and engineering, or particularly smart in any field but infiltration.
In the final season of Buffy the Vampire Slayer, Big Bad The First, who's basically pure, unconcentrated evil, is taunting Buffy during a battle. The First starts quoting Slayer lore about "one girl to stand alone against evil." "There's that word again. Alone," says The First. The First goes on to mock Buffy for always being alone as the Slayer and never being able to fully connect with anyone. This gives Buffy an idea. Sick of being the lone Slayer, she cooks up a plan with Willow. Before the final battle, Willow uses her magic to turn all of the potential Slayers in the WORLD into full Slayers, complete with all of Buffy's powers. Needless to say, this newly formed army of Slayers makes quick work of the First's army of prehistoric vamps in the final battle. Man, Joss Whedon seems to really love this trope!
The First also dug up the Scythe that allowed Buffy to execute this plan in an attempt to use it for itself, and then revealed the location of said Scythe by luring Buffy into an ambush where it was held (rather than, say, any other location in Sunnydale). The First basically spent the last 5 episodes of the series juggling multiple Idiot Balls in order to make its eventual defeat remotely plausible.
Chalk it up to Caleb being enough of a Card-Carrying Villain to lure Buffy into an ambush with "I have something of yours" so that he can get in extra Evil Gloating about this being true and her being unable to recover it.
Also used in season 3, where the Mayor's attempt to clean up loose ends by having a volcanologist who could give the Scoobies useful information killed backfires by leading them right to that information. Being a Joss Whedon show, this is Lampshaded, with said lampshade hanging immediately mocked as such.
Wesley: Ah. By attempting to keep a valuable clue from us, the Mayor may have inadvertently led us right to it.
Buffy: What page are you on, Wes? 'Cause we already got there.
Later in the same episode, Faith poisons Angel to keep him out of the fight and keep Buffy distracted looking for a cure. Ends up backfiring as the cure turns out to be Faith's blood. And considering how they kill the mayor, if Faith hadn't poisoned Angel Buffy wouldn't have been able to lure the mayor into the trap. Joss really, really, really, really, loves this trope.
Another season 3 example. Faith (before Face-Heel Turn) lures an ancient vampire and his gang to Sunnydale. Buffy fights and stakes the vampire twice, to no avail. The vampire taunts her, saying that she'll need a bigger stake. This gives Faith the idea of picking up a wooden pillar and using it as a bigger stake, successfully dusting the vampire
In the LOST Season Six Finale, it turns out that the Big Bad's centuries-long Gambit Roulette worked exactly as planned except it also completely stripped him of all his powers and enabled Jack to beat him to death and toss him off a cliff. Also, his murder of Sayid, Jin, and Sun gives the others the Heroic Resolve to kill him instead of simply leaving him on the island like they had planned, leading to the above success of his plan.
In Once Upon a Time, if Regina had not been completely hellbent on running Emma out of town, she would have left completely of her own volition.
The candle Cora had given Snow allowed Snow to kill her and save Rumple's life. Also, she wanted to "turn Snow White's heart black as coal" for revenge against Snow's mother. She would succeed but it comes back to bite her hard.
In Star Trek: Enterprise, the Romulans attempted to disrupt possible peace between the Andorians and Tellarites by using an advanced holoship which could disguise itself as any other ship to attack both sides. Because one of the Andorian ships they attacked happened to belong to Shran, a friend of Archer, Starfleet got involved and the ensuing mess resulted in the beginning of the Federation, their greatest foe for centuries to come. They really dropped the ball on that one.
In Star Trek: Deep Space Nine Damar has become an ineffective alcoholic. Weyoun's constant hectoring, debasement and reminding him of how powerless he is enrages him into a Heel-Face Turn where he swears off alcohol, frees two federation officers and leads the resistance that eventually throws off the dominion. Nice job Weyoun!
The Goa'uld sowed the seeds of their own eventual destruction by raiding Earth in "Children of the Gods". By killing four guards and kidnapping a fifth (not to mention kidnapping Daniel Jackson's wife later), they managed to piss off possibly the only civilization in the galaxy that was militaristic, creative, and—let's face it—insane enough to bring them down.
The Villain of the Week of "Space Race" tried to rig the eponymous race so that a pure human would win, because he perceived a pro-Serrakin glass ceiling blocking his advancement in a Mega Corp.. In actuality he hadn't been promoted or given a raise in so long because he was under investigation for corruption, but the investigators didn't have enough evidence to indict until he supplied it by rigging the race.
In MythQuest, an evil god named Gorgos tries to destroy myths by causing the protagonists to accidently change them. Unfortunately Gorgos says Alex's name a bit too soon and distracts Alex, which causes him to inadvertantly re-enact the myth correctly and save the world.
Roxana kills Sparadrap's pets in Season 3 finale / mid-way through the third novel. In the webseries version, it turned out to be one of the protagonists's Berserk Button. In the novel version, it was part of a string of bullying that gave The Cavalry time to show up.
The leader of Relic Tracker's guild got Caught on Tape from gloating about his plans in front of the very people who ended up in a Frame-Up because of them.
In The Bible's Book of Esther, Haman goes to ask king Xerxes for a death warrant for his hated rival Mordecai, the representative of the Jews. Xerxes, who happens to have been reading the royal archives, asks Haman how he should reward a man who has done a great service to the king. Haman thinks he's talking about himself and proposes an elaborate celebration, only to find to his horror that the king is actually talking about Mordecai, who had saved the king's life a while back. Haman winds up having to carry out his own plan to publicly honor Mordecai. This is just the beginning of his Humiliation Conga.
In renditions of the part of The Bible where Jesus tells Judas that he's going to betray Him, it's often said that "at that moment, Satan entered into him" or something to that effect. So what we're saying here, is that although Satan may have caused Judas to betray Jesus,the results of Jesus' death led to the cleansing of humanity's sins and the founding of Christianity,which means that Satan's plan(if there was one) failed. Nice job fixing it, Satan!
In the Captain Scarlet and the Mysterons episode "Spectrum Strikes Back", the Mysterons try to kill a committee taking a look at some anti-Mysteron prototype equipment that could be useful. In the end, all the Mysterons essentially achieve is provide a spectacularly successful field test for the stuff that proves its worth.
In the comedy fantasy series Elvenquest, Lord Darkness, the Big Bad, frequently ends up unintentionally saving the protagonists from the consequences of their own mistakes.
In the the world of Innistrad in Magic: The Gathering, the angel Avacyn used to lock demons away in an artifact called the Helvault, until she was tricked by the demon Griselband and the two were sealed together. Losing its guardian angel, lots of bad things happened in Innistrad, until the necromancer Liliana Vess decided to break the Helvault to kill Griselband without knowing that it would also release Avacyn.
In Exalted, when the Great Contagion was killing the majority of Creation, The First and Forsaken Lion got The Fair Folk to invade, destroying fully half the territory and killing many of the Contagion's survivors. The problem? The Balorian Crusade was repulsed, and the infusion of Wyld energies may very well have helped Creation fight off the effects of the Contagion, thereby allowing it to survive. Falafel's Neverborn master was quite angry, to the point where it bound him into his armor. Painfully.
And exiled him to a fortress that was essentially in the middle of nowhere.
Which of course delayed and inconvenienced any number of his extremely effective war plans to destroy Creation more thoroughly this time. So... nice job fixing it...Cthulhu
The Neverborn seem to have a history of sabotaging their own plans to further the cause of Oblivion. Between the First and Forsaken Lion getting spot-welded into his own armor for not destroying enough of creation, and Princess Magnificent almost getting thrown headfirst into Oblivion for losing to the gods behind the city of Great Forks, there's a reason most of the other Deathlords have been twiddling their thumbs for millennia. They don't want to see what the Neverborn will do to the next guy who fucks up.
Alternative Character Interpretation: We're told, explicitly, that most of the Deathlords only agreed to kill the world so they could enjoy using the power they were given to rule over its dying husk. Is it really a surprise that most of them drag their heels? You can't rule the world if you kill it.
Here's a short list of the ways the Ebon Dragon bollocksed up the Reclamation. First off, he included rules that make the Infernals have to act like B-movie villains every so often, but said nothing about who they have to do it to. Instead of granting the Infernals their own innate Charms, he and the other Yozis decided to make it so they share Charms with their patrons... which means not only do the Infernals get access to the high-level Charms that make the Yozis worlds/gods, they could conceivably make their own Charms and infect their own patrons with their particular mindset. Oh, and then there's the Heresy Charm Set... So basically, what you've got is a Hell-forged superpowered being who needs to act like a bastard to someone, has access to god-like power, and can sever the ties with their demonic masters. That sound you just heard was the Shadow of All Things realizing he just invented his Bastard Understudy... Which, again according to his basic nature, might be All According to Plan.
And, of course, the big one that sets the whole setting off. Creation has been in a precarious position for centuries, with the overworked Sidereals, the Lunars driven to the edge of the world, the heavily corrupt (or absent) gods, the almost equally corrupt Realm, the forces of the Underworld massing, and the Fair Folk being just barely kept in check. Into this comes the person controlling the Realm (and its big superweapon that keeps most of the other big enemies at bay) mysteriously disappearing, bringing it to the verge of a civil war that could tip Creation over the edge. And then... the Neverborn and the Yozis conspire to break open the Jade Prison, and use its captives to make their own Exalted. Half of those captives escape them. They become the Solar Exalted.
In Super Robot Wars the villains have brainwashed one person's girlfriend to forget they fought together, and make her think he was an enemy. By reminding her of a memory of when they were together, she gets paralyzed and stands their indecisive. Then a group of said villains minions show up and threatens the guy's life, accidentally triggering the girl's memories of her relationship, immediately snapping her out of the brainwashing and rushing to protect the guy. Whoops. Gets Lampshaded.
Happens a lot of Ace Attorney, as a lot of times the culprits themselves do or say something that ends up backfiring horribly on them. Some notable cases:
In the original, Damon Gant accidentally makes a piece of incriminating evidence legal and incriminates himself, instead of Ema.
In Justice for All, Phoenix is trapped in a no-win scenario: either he gets his (guilty) client off the hook and send an innocent woman to jail so he can get his assistant back, or he throws his (guilty) client to the wolves and gets his assistant killed. The guilty client himself accidentally provides a third option: because he was going to use the crime scene videotape to blackmail his assassin, Phoenix gets the assassin to let go of his assistant of his own accord by proving his client's deceit. Then Phoenix is free to send his client to jail with no repercussions.
In Trials and Tribulations, Luke Atmey would have gotten away scot-free with murder if he hadn't slipped up once and revealed he knew Ron was wearing his costume when supposedly Luke wasn't even at the crime scene.
In Trials and Tribulations, Phoenix falsely presents a bottle of ear medication as the poison Furio Tigre used to kill the victim. Tigre calls him on it, and in his rage, describes the real vial that he used. Of course, Tigre, having been absent when the real bottle was presented in court, only had one way of knowing that information...
Releasing the Cornstalker in the final chapter of Touch Detective 2 1/2 would seem to fall under Stupidity Is the Only Option... except that this is all he manages to pull off — his efforts to steal the treasure only succeed at helping Mackenzie safeguard it and escape the aliens who have abducted them.
In one of the endings of Mega Man X2, Sigma leaves the protagonist (X) at a total dead end, leaving him alone with his Brainwashed and Crazy old friend, Zero. However, after he leaves Zero to fight X, Zero is able to break out of his crazyness and actually opens an otherwise unreachable path to the final boss.
In Mega Man X5, Sigma may or may not have done so again, as Zero is severely injured and possibly killed offscreen. He miraculously recovers, possibly with Sigma's intervention, but his Superpowered Evil Side has been reawakened (definitely Sigma's work), which gives him only one objective: to kill X. However, as with X2, he eventually ends up turning good again and actually saves X from Sigma after X is weakened from a fight, something he probably wouldn't have been able to do if he was still stuck in the wreckage of a spacecraft and/or dead.
In Left 4 Dead, many an eager-to-help Tank user has freed a Survivor from the clutches of a Hunter or Smoker, or the Charger in Left 4 Dead 2, by going to attack said Survivor.
In Half-Life 2, toward the end of the game, Gordon Freeman (the player character) goes through a weapon confiscator created by the Combine (the enemy faction). It destroys all his weapons except for the Gravity Gun, which the confiscator is unable to destroy. Instead, the confiscator malfunctions and actually ends up making it more powerful. So powerful, in fact, that it completely outclasses every other weapon in the game.
The Collectors' attack on Shepard at the beginning of Mass Effect 2 ends up putting Shepard in a position where he/she has no choice but to cooperate with Cerberus...who happen to be the only power in the galaxy who actually believes the Reapers are coming and is prepared to throw their full backing behind Shepard's quest to stop them.
In Portal 2, Wheatley, when suffering from test withdrawal, he decides a good way to fix it is to move the test chamber Chell and GLaDOS are in as close as possible to his lair.
Metal Gear Rising: Revengeance: Over the course of R-03, villains Jetstream Sam and Monsoon relentlessly taunt Raiden by drilling holes in the logic behind his desire to protect the weak, claiming that simple blood-lust is the only reason he that he continues to remain on the battlefield. Their aim was to demoralize and mentally destabilize him, rendering him easier to kill. Except, whoops, Raiden ends up agreeing with them and taps into his Ripper persona to make himself stronger than ever, giving him the edge he needs to defeat and kill Monsoon. One thinks that there may have been better ways to deal with the repressed homicidal battle-monger than egging him on into abandoning his more benevolent tendencies.
Valkyrie Profile: Lezard Valeth in the best ending. Most of his appearances and villainous actions actually are required for the best ending to even occur. Lezard Valeth kills Mystina, who becomes very loyal to Lenneth, which is why she refuses to serve Hrist and helps transfer Lenneth's soul temporarily to a homunculus. Lezard kills and mutilates the body of elves to create a homunculus for himself and Lenneth, which is needed to store Lenneth's soul when Hrist takes her body. Lezard transfers his soul to a homunculus and sacrifices the Philosopher's Stone to survive Ragnarok and grant himself immortality, which allows him to be present to fight Hrist. He is one of the four people willing and able to fight Hrist to retake Lenneth's body due to his obsession with her. The only villainous thing Lezard that does not contribute to getting the best ending is killing Lorenta and her husband (it is required to see this event to get the best ending, but Lorenta is a basic einherjar that never gets mentioned in the plot after she is recruited).
In The Legend of Spyro: Dawn of the Dragon, Spyro, Cynder, and Sparx have been frozen in crystal for three years, allowing Big Bad, former Sealed Evil in a CanMalefor to run rampant over the world with an iron claw and is days away from succeeding in his ultimate plan to destroy the world. Then some mooks decide to break them out of the crystal to sacrifice to a giant monster, they escape, allowing them to turn the tide against Malefor and save the world. They also tethered the two together with a pair of magic necklaces, but this allows the two to work together much more effectively and ultimately makes them realize their love for one another.
Also, in a way, Malefor is guilty of it for what he did to Cynder, as it gave Spyro something important to fight for, something Spyro himself even makes mention of when Cynder is corrupted again.
In Chrono Trigger, when Dalton steals the Epoch, he converts it into a flying vehicle. Without this modification, the party would never be able to reach most of the sidequests.
This is even lampshaded, probably unintentionally, with multiple party members having lines such as "I guess we are actually in his debt." after the fight.
This actually happens again at the end of the game when Darkrai (disguised as Cresselia) actually tries to kill you because to him, it's the only way the world will be saved, and that Darkrai was actually behind everything all along. Fortunately, the real Cresselia shows up and exposes Darkrai's true identity. Had he not done this, you wouldn't have known about his backup plan in the first place.
In Halo, mankind is right on the cusp of extinction in its war against the technologically and numerically superior Covenant, and then the Prophet of Truth makes the decision to betray the Elites, which results in a huge portion of the Covenant allying with the humans; during the last large space battle in Halo 3, it's the Elites who are largely responsible for wiping out Truth's fleet.
In Mother 3, Porky introduces the world to the evils of materialism and money. This seems to just be a distraction from his true plan to destroy the world. If he didn't indulge in this, the protagonists may have very well stayed at home, allowing his masked assistant to pull the Cosmic Keystone and destroy the world without any interference.
In Mario & Luigi: Partners in Time, this turns out to be the result of Bowser kidnapping Princess Peach. It turns out that the "Princess Peach" the brothers rescued from beneath the Koopaseum was actually Princess Shroob in disguise, and was planning on assuming her guise. Bowser, however, thwarts this plan by taking her away.
Cave Story. After you defeat the Corenote depending on which ending you're going for, you're either defending yourself after the Core attacked you without provocation, or you were already planning to destroy the Core anyway as a last-ditch effort to defeat the Doctor, Misery and the Doctor pop in to (sort of) save the Core because it's the only thing keeping the island afloat. Misery then tries to kill you by flooding the chamber... which opens the way out of the Labyrinth, ultimately allowing you defeat the Doctor for good.
L.A. Noire has Cole demoted to Arson due to his affair with Elsa being exposed. But the good news is that he could get close to the Suburban Redevelopment Fund. The best news is that Roy Earle, the one who exposed his affair, is not happy about this.
Also happened in Wrath Of The Lich King in the Death Knight intro sequence. The eponymous Big Bad has just thrown the order of The Knights Of The Ebon Blade at a small church in the western plaguelands as a Batman Gambit to lure out one Paladin, Tirion Fordring. Not only does this succeed in bringing Fordring back out into the world from Exile, but it causes the merging of two paladin orders to focus on killing The Lich King. Much worse is that in the process of causing this, a long time cursed sword that was in the hands of the commander of the Ebon Blade is purified by the mere touch of Fordring. The Sword? Ashbringer. It ends up shattering Frostmourne into pieces and ultimately causes the BigBad's defeat at the top of Icecrown Citadel.
Sylvanas' backstory is also an example of this. During Warcraft 3, while Arthas is invading Quel'thalas, Sylvanas and her squadron are a major thorn in his side. Despite him (depending on the player) outnumbering her quite a bit, Sylvanas' determination and ingenuity make her a major threat to him. Then, Arthas finally kills her, and instead of breathing a sigh of relief that he'll never have to deal with her again, he decides to resurrect her so he can enslave her and make her miserable. This backfires when Arthas' power weakens temporarily, and Sylvanas immediately frees herself, tries to kill him and fails, and then founds the Forsaken, who are eventually instrumental in his destruction (even if there was collateral damage). So Arthas created one of his biggest enemies, when he could simply have left her stay dead.
The attempt to silence Vol'jin in Pandaria during the 'Dagger in the Dark' scenario may have began Garrosh's downfall, as Vol'jin survived his assassination and hid out till the time was right to start a Darkspear revolt against Garrosh's Horde. He was able to gather a number of Horde heroes, unite Thrall, Lorethmar Theron, Baine Bloodhoof(Who's father was killed in a Mak'gora), Dark Lady Sylvanas and Jastor Gallywix against Garrosh, and even forge a truce with the Alliance(Lead by King Varian Wrynn) and their heroes. And in a twist of irony in the end, Garrosh Hellscream is dethroned by the heroes and detained by Taran Zhu while Vol'jin was chosen by Thrall as the new Warchief. All of his allies bow to him in respect.
In the The Elder Scrolls V: Skyrim expansion Dragonborn, the main quest starts with cultists attacking the player. One of the cultists has a note with orders from Miraak, the first Dragonborn. If he had never tried to get cultists to kill the player, the player would not have known about him, and he would have been able to leave Apocrypha and take over Solstheim.
An instance of this occurs a few games earlier in the Tribunal expansion for The Elder Scrolls III: Morrowind. Almalexia tasks the Nerevarine with reforging the original Nerevar's blade TrueFlame, presumably to use against a deranged Sotha Sil. However, SHE is the villain, and basically gave one you one the best swords in the game. Guess which weapon most players use to defeat HER? Go on, guess!
Similar to the Dragonborn example, the entire plot of Tribunal is kicked off by assassins attempting to murder the Player Character under orders from a villain the player wouldn't have known about otherwise.
The F-Con trio in Tron 2.0 make some really foolish mistakes. Yes, they kidnap Alan and successfully intimidate him into forking over the information needed to make the digitizer run...but then they lock the man who programed Tron and Ma3ain a room full of old computer parts, giving him the ability to at least make contact with his son and upload Mercury to help. Then, they decide to dispose of him by shooting him into cyberspace, reuniting him with his son and Ma3a and giving him access to crash the datawraith server from the inside.
Not to mention, the entire game might not have happened if not for Alduin. The Dovahkiin would have died a nameless nobody in Helgen if Alduin hadn't interrupted their execution by trying to kill them.
On a low level every time you come to a dead end in Doom3 some minion will burst through the wall / locked door or knock over something you can use as a bridge. In a more serious example the bad guy's plan to lure you to hell has the minor flaw that hell contains the only weapon that gives you the possibility to thwart his evil scheme.
Devil May Cry has Trish revealing herself to be working for Mundus. By doing this, Dante severs his ties with her until they finally made up in the end.
The villain in Max Payne 3 is Victor Branco. One of the major facets of his plan involves getting his entire extended family killed by local extremist groups, which means he'll inherit direct control of his family's money from his late brother Rodrigo. As such, he needs a security guard who's good enough to protect his family from casual threats, but not good enough to protect them from Victor's conspirators. His solution is to hire Max Payne, a drunken slob with a history of violence. Unfortunately for Victor, Max is very bad at keeping people alive, but he's very, very good at making people pay for their crimes. If Victor had hired almost anyone else on the planet to be his fall guy, his entire plan would've worked out just fine.
Fallout: New Vegas used this trope on purpose. Nice job, Ulysses, arranging a lethally dangerous delivery mission for the person you wish death to. Turns out, that person is hardier and tougher than they look, and the mission turns out to be marvellously rewarding. Now it's them and not you who became the NCR/Legion's top field agent, Mr.House's second-in-command, or simply gave New Vegas its independence and has the support of a grateful population.
At one point in The Legend of Zelda: Twilight Princess, Zant curses Link to stay in wolf form by putting a black crystal in his head. This comes to bite him in the ass later, as the power of the Master Sword allowed Link to return to human form and keep the black crystal, allowing him to switch forms at will. This is lampshaded by Midna right before you actually fight Zant.
He does this repeatedly by sending his Shadow Beasts after you. They fall from the sky via a portal that remains when you kill them, which you can then warp out of whenever you want with Midna's power.
Also, creating the Black Mages was certainly a good plan...except that your Super Prototype is highly likely to be one of the four people killing you at the end of the game.
In Ib, Garry suffers Laser-Guided Amnesia if he is captured by the dolls and is unable to escape. Mainly he forgets what he just learned about Mary. Namely, that she's a painting. Later on, Mary tries to attack him...which causes him to remember everything he forgot. Oops.
The Gloria's Theater level in Psychonauts revolves around finding new scripts and producing a series of plays so Raz can ascend the stage to the catwalks and battle the Phantom, and oddly enough, the first script you find, the one that sets almost the entire solution process in motion, is given to Raz by the Phantom himself, aka Jasper.
In Batman: Arkham Origins the Joke Boss Electrocutioner is brought in to kill Batman. Joker kills him for his earlier defeat and general impudence. But the mere fact of his existence at the meeting allows Batman to find them. Furthermore, his electric gloves are vital to proceed, culminating in saving Alfred and allowing Batman to stop Bane's heart and later restart it long enough for Joker to willingly leave his death trap set up to force Batman to kill someone.
Star Trek Online episode "From the Ashes", mission "Turning Point". Colonel Hakeev of the Tal Shiar tries to bust up the international summit on Khitomer and pin it on the Romulan Republic, in order to prevent the Federation and Klingons from giving protection and aid to the Republic. He gets caught red-handed by Captain Ja'rod of the IKS Kang, and after Commander Temer dies shielding Ambassador Woldan from a Tal Shiar bomb the two superpowers are greatly impressed and decree that the Republic has the right to exist as an independent nation (and therefore can receive military support from them).
The third and final Monster Girl Quest has Ilias, who's spent God only knows how long trying to kill monsters and keep them and humans apart, finally just decide to kill both and rebuild the world anew. Humans and monsters band together and join forces to fight her attack off, which greatly helps the two groups come to understand one another and start to co-exist.
In Darths & Droids, Pete gets egotistical and gives everyone a + 1 morale boost just by watching R2-D2 fly. This gives Annie enough of a stat boost to dodge a quintuple guillotine.
In an early story arc in Dominic Deegan, Greg, a white mage, is infected with the "Blight of the Undead", a curse that would essentially turn him into an undead abomination. It was kept in check by his devout use of White Magic. Later on, in a confrontation with his eldest brother Jacob (a Necromancer), he rips the blight out of his body through his un-blighted parts. Jacob then learns the hard way that the Blight was acting as a magical Restraining Bolt, and with it gone, Gregory's magical power increased exponentially. And since white magic is incredibly powerful against necromancy, Greg is able to strike Jacob down with one (albeit titanic) magic blast.
During the battle between Dominic and Celesto in the Storm of Souls arc, Celesto uses his powers as the Champion of Chaos to trap Dominic and try to use him as fuel for the Weapon of Mass Destruction. Cue Dominic gaining a level in badass when it turns out he's actually the Champion of Balance and chaos was the last force he needed to experience in order to gain full power, beat Celesto, stop the Storm, and save the world.
Additionally, Florence lampshades that she would not have been aware of Gardener in the Dark in the first place if not for Edge trying to save himself from it, nor would she have been able to stop it without Sam's criminal knowledge of social engineering and sabotage.
Florence: All my life, I've been taught the values of being a good citizen. No one ever told me that when the chips are down, civilization needs the rotten ones.
The main character of Girl Genius, an orphaned young lady named Agatha, wears a locket-type amulet with pictures of her parents in it. The locket is her most prized possession, given to her by her paternal uncle Barry shortly before he mysteriously departed, leaving Agatha in the care of her adoptive parents, the Clays. She never removes the amulet for very long and is never far away from it. Agatha struggles to be an engineer and inventor, like her beloved uncle, but fails constantly due to the severe and sudden migraine headaches she suffers whenever she tries to concentrate. Near the beginning of the story, a pair of drunken soldiers accost Agatha on the street. One snatches her locket, planning to sell it for a little quick cash. It turns out Barry designed the locket to suppresses Agatha's "spark", her innate intelligence and engineering talent. With the amulet gone, Agatha becomes a super-genius. She converts a steam-powered tractor into a complex robot programmed to seek out the amulet and return it to her, an impressive feat in and of itself made even moreso by the fact SHE LITERALLY DOES THIS IN HER SLEEP!
It also turns out the waves emanating from the amulet are extremely dangerous to anyone other than Agatha, as the loutish soldier who stole it soon finds out. The amulet ends up killing him by slowly destroying his brain. His fellow soldier, actually his younger brother, realizes the amulet is the source of his brother's demise when it is accidentally broken open, revealing the mechanism within. The young soldier uses the address engraved on the back of the locket to track Agatha down, looking for vengeance. Normally, the amulet would dampen Agatha's genius ability when brought in close proximity to her, but the young soldier was nice enough to switch the thing off. The now brilliant, clear-headed and more confident Agatha easily out-smarts and overpowers her would-be attacker and turns the tables on him, tying him up and reclaiming her beloved keepsake.
Later in the story, an evil entity known as "The Other" possesses Agatha and gloats over an incapacitated Baron Klaus Wulfenbach, sworn enemy of The Other who is also hunting down Agatha so he can lobotomize her and permanently destroy her spark. The Other notices Klaus is carrying Agatha's amulet, which has a trilobite design on it, the symbol of Agatha's real family, the Heterodynes. The Other decides to use the amulet to pass itself off as a legitimate Heterodyne heir and lay claim to their family castle, stuffed full of amazing and highly dangerous technology & research. As soon as The Other slips the amulet around Agatha's neck, however, she is able to regain control. That's TWO villains each cancelling the other out.
Xykon breaking Roy's beloved sword both filled the fighter with a vengeful resolve, and forced him to grapple the lich bare-handed. He promptly hurled Xykon into a trap-warded gateway, which blew the undead sorcerer's body to pieces: something Roy certainly wasn't powerful enough (yet) to accomplish with sword strikes.
Also, Xykon is an epic-level sorceror, the Order has no chance of defeating him. Except, Xykon broke Roy's sword, and Nale sent Roy on a dangerous sidequest to get it fixed, which has resulted in Roy's sword being made of a material that is very effective against undead.
One arc concluded with Xykon's attempt to Breaking Lecture the recently defeated Vaarsuvius not only failing, but actually lifting V out of a pre-existing case of Heroic BSOD, and giving V advice that's made him/her more effective than s/he'd been even before the Heroic BSOD.
Nale's actually pretty good at this. Elan took a level in the Dashing Swordsman prestige class because Nale stole his identity. Later, one of his more impressive momentsnote killing Malack the vampire cleric backfired doubly: It gave Vampire-Durkon his free will back. Durkon immediately killed one of Nale's teammates and rejoined his friends. Then he threw the feat back in Tarquin's face as proof of how he didn't need or want Tarquin's protection. Malack was Tarquin's best friend and fellow party member. Filicide ensued and the Order was down one recurring nemesis.
Slightly Damned: All that was needed to remove Kieri's magic restraining cuffs & collar was for her name to be spoken. Guess what the villain shouts out between swears at the top of her lungs.
Captain SNES: The Game Masta features this trope in spades. When fighting Milon, he offhandedly says that he's invincible as his unobserved power is infinite - which causes Lucca to use her SightScope to observe his power and turn it into a finite number. Later on, Palom casts Virus on Milon, enraging him and making him use his "Eternity In A Second" attack to take the next few thousand turns. He says that he'll enjoy watching everyone squirm, unable to do anything - and then dies. (Turns out Virus inflicts Sap, which depletes a little HP each turn - and when Milon takes thousands of turns in a row...)
Sluggy Freelance: In "The Stormbreaker Saga", Zoë, trapped in the past, is prophesied to defeat the demon K'Z'K but also about to be executed by the fairly dim-witted King Sighard of Trent. All she has left is a shotgun (they let her keep it because no-one has any idea what it is) with one shot. That wouldn't do much good, except that K'Z'K has turned the executioner into one of his undead minions, and he tries to kill the king instead — giving Zoë a chance to use that one shot to save the king and impress everyone with her "magic", convincing them that she is the Chosen One. Thus, K'Z'K unknowingly helps a far more dangerous enemy survive when trying to eliminate a lesser one.
You can sometimes trick trolls into admitting what theyï¿½re doing if you get them to brag. This leads to their credibility being destroyed or the moderater's banning their asses, and will then make the board harder to be trolled by anyone. Nice job, idiots.
Worm has the ABB. Their actions caused Skitter to join the Undersiders, the superheroes and supervillains of the city to join forces against them, and Lung's second loss to Skitter when he attempts revenge for their first fight. It also allows her to carve out his eyes when she beat him again, making him easier to capture by the heroes. This wipes out the ABB.
In Noob Season 3 finale of the webseries, Roxana, just For the Evulz, decides to kill Sparadrap's pets in front of him. That's how we find out that the series Stupid GoodKindhearted Simpleton has a Berserk Button. The novel version of the scene reveals that The Cavalry arrived in time due to Roxana taking time to Kick the Dog rather than immediately killing Sparadrap and his teammates (which she could have done easily). That season / novel also had someone get Caught on Tape due to admitting a misdeed while online in a MMORPG. In front of the very people he framed for said misdeed. That include a player that is frequently loading videos of in-game events on her blog.
In Avatar: The Last Airbender, Aang has one of his chakras blocked by getting hit by Azula's lightning in the Avatar state. He can't get to that state anymore, and he's not skilled enough in the bending he's learned to take on Ozai. In the middle of the fight, Ozai goes in for the killshot, with Aang resisting with all the strength he has left. The blast throws Aang onto a small rock outcropping... right onto the scar caused by Azula's lightningbending attack. This unblocks the chakra, allowing Aang to reach the Avatar state and for epicasskicking to ensue. Cue Ozai's Oh, Crap expression.
Combustion Man manages to intercept a messenger hawk headed for the Fire Nation with the information that Aang is still alive, as Zuko wanted to eliminate Aang discreetly. This prevents the rest of the Fire Nation from learning about Aang until the Day of Black Sun.
Ozai committed this two years before the story started. If he had never banished his son, then he would've won. Zuko himself outright states this to him in the finale, calling it the best thing he could've ever done for him.
Azula has instance of this in Book 3, when Zuko states he's angry over something he doesn't know about, some prodding by Azula (though Mai and Ty Lee took as well) caused Zuko spit out that he's angry at himself, which helps with his Character Development that leads to his Heel-Face Turn. Which leads to Mai's Heel-Face Turn a few episodes later when she sees Zuko about to be dumped in boiling water on Azula's orders. Which leads to Ty Lee'sHeel-Face Turn in short order when Azula tries to attack Mai right in front of her.
Even before the scene during "The Beach", which the above example explains, Zuko was worried if Ozai would finally be satisfied with him after coming home with the reputation of killing the Avatar. Azula calls him dumb and tells him that the only person he should be trying to satisfy is himself.
In The Legend of Korra, Amon uses his powers to remove AvatarKorra's ability to bend water, earth, and fire. the elements she had mastered. He also inadvertently unlocked her ability to bend air, and to connect to her former lives, one of which gave her back all her bending, plus the ability to restore the bending of anyone else Amon had "equalised." As far as this trope goes, it's a doozy.
And the biggest example of this: in the very first episode, when Starscream is "just saying goodbye!" to the unconscious Autobots on Earth, he actually revives them. Remind me again why Megatron keeps him around?
A list on Cracked.com put the action firing at the ship, and that awakened the Autobots, as two of the five reasons Megatron should have fired Starscream years ago. To drive the point home even more on how bad a henchman he was, all five reasons came from the first episode.
Then again, if the other Decepticons followed his lead, they might have won the war right there what with the Autobots being in stasis lock.
Probably the best example of Starscream's treachery helping the Autobots is in Transformers Animated. Megatron probably would have killed the Autobot repair crew and gotten his hands on the Allspark if Starscream hadn't put that explosive on his back.
Same with the original G.I. Joe cartoon; a number of times the Joes are beaten, but Cobra Commander has to drive it in (often at the objections of Destro), somehow giving the Joes the chance to overcome their predicament. Strangely enough, Cobra's high-rankers prefer Serpentor to him because of this attitude, and yet Serpentor occasionally falls into this trope as well.
In Turtles Forever, the 2003 Shredder is revealed to have one weakness- the Technodrome's Death Ray. Just as the Turtles manage to push him into it, Bebop and Rocksteady accidentally unplug the thing- as Shredder gloats over his apparent victory, they plug it back in, annihilating him in the process. Bebop and Rocksteady saved the TMNT multiverse this way.
In Rogues in the House, the Turtles have been incapacitated and Shredder orders Karai to execute them to prove her loyalty. She's willing to do this and raises the blade, but Hun decides that this is too boring, and thus frees Leo so that they can duke it out. Leo lectures her during this fight, which ultimately persuades her not to kill them
In the older Teenage Mutant Ninja Turtles cartoon Krang had made Super Rocksteady and Bebop robots, which were incredibly strong and intelligent, and could effortlessly defeat the turtles. Until the regular Rocksteady and Bebop accidentally expose them to lightning.
In the 2003 version, the Utron Shredder did a much better job of “fixing it”. Although he committed many horrendous crimes that caused anguish to so many people (murdering Splinter’s master, burning down Casey’s father’s store – and possibly killing him too – and kidnapping dozens of New Yorkers and turning them into horrid monsters), as Donatello explains, he originally put into motion a set of Disaster Dominoes that led to the Turtles’ very creation and his own undoing. (And the biggest irony is, he never learned this.) To summarize:
Donatello: If the Shredder had never made the Utrons crash in the first place, they’d have never developed the ooze, and if they’d never developed the ooze, we’ve never have been mutated, and if we’d never have been mutated, we’d still be eating fish flakes in some kid’s aquarium right now!
In the stop-motion animation special Here Comes Peter Cottontail, Peter Cottontail and the villain Irontail are competing for the job of head Easter Bunny. Whoever delivers the most eggs wins. After missing delivering eggs on Easter, Peter tries to deliver the eggs on other holidays, but to no avail. In an attempt to make sure Peter never gets to unload his supply of Easter eggs, Irontail casts a spell on them that turns eggs green inside and out. Irontail believes that he's won — no one would want green eggs. But then, the next holiday Peter tries to deliver the eggs on turns out to be St. Patricks' Day. As a result, he successfully gives away all the green eggs, and becomes the head Easter Bunny. Irontail, meanwhile, is forced to sweep the bunny trail in the ending credits.
In an odd twist, Nox, the Big Bad from Wakfu, actually purposefully attempts to invoke this trope. He's a time mage who kills and drains people of their energy (the eponymous wakfu) in order to power an attempt to travel back in time to save his dead family. He is able to happily commit countless atrocities, draining entire nations over the years, because he believes that once he successfully travels back in time it will all be undone. He even manages to kill The Hero and wipe out an entire race in the finale. Unfortunately, his plan fails, and the wakfu that it took him 200 years to collect is barely able to send him back 20 minutes.
In The Powerpuff Girls episode "Forced Kin", an alien force defeats the girls using every single idea Mojo Jojo had ever come up with. Jojo gets so upset at the alien stealing his ideas ("You've. Ruined. My. DREAM!!!!!") that he goes primal and physically forces the alien leader to submit, driving away the attack and becoming the hero.
Mojo Jojo did this again when he used the Professor's time machine to go back to the day when he was inspired to create the girls and prevent it from happening. As it turned out, his kidnapping of the Professor leading to the girls having to rescue him inspired him to try and create three perfect girls of his own. It wasn't until they returned to the present that the Professor realized that the girls that rescued him were his own girls. In other words, if Mojo Jojo had never tried to change the past, Professor Utonium would never have been inspired to create the Powerpuff Girls.
In The Venture Bros. episode "Handsome Ransom", the Monarch corners Captain Sunshine in his sanctum solarium at night, powerless from lack of sunlight and emotionally crippled from seeing him wear Wonderboy's uniform. Rather than just shooting him, Monarch makes a drawn out gloating speech and pulls out a solar beam gun intended to burn him off. It backfires horribly, recharging Captain Sunshine and allowing him to burn alive all of Monarch's mooks, winning the day.
The beginning of season 2 of Jackie Chan Adventures has Valmont kicking the eponymous character off a cliff which results in Shendu possessing him and making them both less effective.
The season 2 finale shows Terra as The Mole, who promptly defeats all the Titans individually. She failed to finish the job, though, so five very angry Titans came back to teach her the error of her ways.
Another example, though not as big: When the Titans East had to watch Jump City while the core team was away fighting the Brotherhood of Evil, they have a very hard time getting the public to accept them. (Being newcomers and all, no-one recognizes them, or even worse, mistakes them for the core team). When Control Freak shows up gunning for revenge against the Titans, he's even worse; he doesn't accept them as "real Titans", and to prove it, sets up a series of attacks on the city designed to "test" them, which push them to their limits. (For example, Bumblebee has to stop a subway from reaching a certain station, as a bomb is mounted on the underside of the train which is timed to detonate upon arrival. The catch: She has to do it at miniature size.) However, the Titans East members avert all five disasters and pass with flying colors, and all of a sudden, they become heroes. You can't deny that they owed this to Control Freak. (They still arrested him, of course.)
In Transformers Prime, a pair of Vehicon Mooks decide to Kick the Dog with an amnesic Optimus/Orion who is beginning to doubt Megatron's plans and protests against them. The beatdown causes Optimus's arm cannons to appear, the ones he had forgotten he had. Then, he uses them to easily defeat the Vehicons and head after Megatron.
In one episode of Aladdin: The Series, Mirage uses a mystical music box to put the entire city of Agrabah to sleep, which in turn anyone who does so becomes one of her Brainwashed and Crazy minions. Aladdin is the last one left, but just as he is about to stop her he finally succumbs to the spell himself and falls asleep, which means within seconds he'll become one of her mindless zombies as well. Just as Mirage starts gloating, the mind-controlled Jasmine and Phasir burst in, which winds up waking Aladdin up long enough to close the box and return everyone to normal. Mirage's own mind-controlled minions wound up being the very thing that ultimately undid her plan!
At one point in the Sandokan cartoon, the Rajah (the Big Bad) has captured Sandokan's island fortress, locked him and his men in their own cell and set a Rube Goldberg Device to blow them up once he and his own forces are a safe distance away. The heroes have no hope of escape, they're doomed...except that meanwhile the other antagonist, the Rajah's ally Lord James, has put in motion a plan of his own to arrange the kidnap of Sandokan's friend's daughter in order to lure Sandokan into a trap. When she's kidnapped, her father's lieutenant hurries to the island to seek Sandokan's help, finds the heroes locked up and defuses the bomb in the nick of time.
Invoked and lampshaded in the Regular Show episode "Do or Diaper". Muscle Man provokes Mordecai to agree to a bet which states that if Mordecai can kiss his Love Interest Margaret by Friday night, Muscle Man will have to wear a diaper for a week, and if he can't do it, obviously Mordecai would have to wear the diaper. Mordecai and Margaret go on a date, and in an unlucky series of events Margaret finds out about their bet when she notices Muscle Man and Mordecai's friend, Rigby, following them around the entire evening. Mordecai has to explain the bet he had with Muscle Man, which Margaret clearly isn't very happy about. Though to help her understand his actions and earn her forgiveness he is forced to be honest and apologize to her, which leads to the Love Confession being dropped. It might seem like Muscle Man did Mordecai wrong by provoking him to agree to the bet and blowing his cover later, but he really made Mordecai learn something and helped deepen his and Margaret's relationship. Mordecai is even shown wearing the diaper with a smile at the end of the episode, explaining that "he's just happy because Margaret was having a great time on their date, and that means she must like him".
She-Ra: Princess of Power: In "Horde Prime Takes a Holiday", if not for Skeletor trying to take over Horde Prime's warship, Hordak would have frozen She-Ra and He-Man.
Hordak and Skeletor unknowingly do it to each other in "Loo-Kee Lends a Hand". If not for Skeletor's plan to capture Prince Adam, who knows how long would it take Loo-Kee to find Prince Adam and ask for his help or how much damage the Horde would have done by then? Also, if not for Hordak freezing time for the rebels, Loo-Kee wouldn't have gone to Eternia and ruined Skeletor's plan to break into Prince Adam's bedroom.
In the season 2 finale, Twilight Sparkle calls out Princess Cadance and calls her evil, which nets her a royal "The Reason You Suck" Speech from her brother, all her friends turn on her, and even Princess Celestia is disappointed in her. Twilight herself is ashamed of her behavior and apologizes. Of course, had "Cadance" who is really QueenChrysalis in disguise just left it at that she would have won. Unfortunately that just wasn't evil enough: instead she banishes Twilight to the caves below Canterlot where she meets the real Cadance, rescues her, and brings her topside to thwart the entire masquerade.
In "Twilight's Kingdom Part 2", if Tirek had stuck to his word to Discord, he wouldn't have given the Mane 6 the final key needed to beat him. Of course Tirek had no way of knowing it'd backfire at the time.
At the end of the first season of Frisky Dingo, Killface's son activates the Annihilatrix, which was designed to push the Earth into the Sun. Instead, it backfires and effectively reverses the damage caused by global warming.
Once in awhile on Wacky Races, Dick Dastardly's machinations would result in giving the other racers an advantage against him. In the debut episode, "See Saw To Arkansas," he gets the racers hung up on a cloverleaf highway exit system. When the narrator asks how he did, Dastardly turns the sign marking the exit around, and the racers immediately take it—flattening Dastardly in the process.