Vampires, the badass creatures of the night who always want to suck your blood, tend to have a lot of weaknesses. Popular tradition holds that you're fine as long as you stay in the sunlight, have some garlic, stay inside your house and refuse to let them in, or even wield a simple cross. In fact, pretty much the only traditional weakness of vampires that's not weaksauce is the whole wooden stake bit, since getting stabbed through the heart with a pointy stick kills most things.
The multitude of fiction involving vampires, though, has led to a multitude of differing weaknesses—including varying degrees of effectiveness. In some settings, vampires are weak to silver, and other religious symbols affect them as much as Christian ones. Then there's the older, more obscure, and even more restrictive weaknesses such as inability to cross running water, or obsessive-compulsive disorder causing the need to count piles of seeds, grains of sand, or other small objects, inability to stand constant bell ringing, and even the need to be invited to enter houses.
On the inverse, many of the works that tend toward "non-standard" portrayals of vampires also go at length to mock the traditional weaknesses.
The Fair Folk are terrific—as in terror-inducing—beings of legend and myth ... and yet, they can be beaten by a stick of iron, a horseshoe, a length of rowan wood, clothes worn inside-out, or a stick of bread.
A popular explanation for the weakness comes from Victorian Era archaeologists, who held that this is all just symbolism for the bronze and stone-working cultures being conquered by iron-working ones. More recent academics (like Dr. Diane Purkiss) have shown there's no archaeological or historical evidence for this.
This is an especially big problem for the Nuckelavee of Orcadian folklore. Widely considered the most malevolent elf in all of Scotland, the Nuckelavee is an eldritch horror that resembles a man on horseback, if the man was fused to the horse and both had all their skin flayed off. It rides through the countryside destroying crops, killing travelers, causing floods and plagues and generally being a harbinger for all things bad. How do you defeat this monstrosity? Fresh water, and burning seaweed. The Nucklavee fears freshwater, so much so that it cannot cross a stream, and hides in its oceanic lair during the winter storms. Likewise, it finds the smell of burning seaweed intolerably offensive. However, don't provoke the Nucklavee, especially with taunting or burning seaweed, as whenever the Nucklavee is offended, it tries to kill all of the horses in the Orkneys with a hideous disease called "Mortasheen."
The Irish/Celtic Dullahan, a fearsome headless fairy that rides at night (either alone or accompanied by banshees) to splash buckets of blood into people's faces — to announce the recipient of a face-full will soon die. They're also a mean shot with a whip, and sometimes drive horse-drawn carriages decorated with human skulls and femurs. There's no known way to actually kill a Dullahan, and the only way to ward one off is to exploit its intense fear of... gold. That's right; the Dullahan, possibly one of the most pants-wettingly scary portents of imminent death, can easily be warded off by one of the metals most commonly used to make jewelry, and which also used to be a standard monetary metal before paper money was widely adopted. Please remember this is more weak sauce in real life than fiction though.
Gold was in no way a common standard for cash; it served strictly for large trade and few people would have carried any that wasn't jewelry.
Werewolves have their share of weaknesses, too; earlier legends provide ones such as having an iron bar thrown over their head - although hitting somebody with an iron bar is pretty incapacitating for most creatures - drawing three drops of blood, or having their name announced one to three times.
The popular weakness to silver weapons is a relatively new invention. It often comes with an immunity to anything not made of silver. Most werewolves that don't have the silver weakness can be killed by any type of weapon, including silver.
Basilisks. Okay, they can kill you if you look directly at them, or hear their voice, or if you touch them, or it breaths on you, but guess what? They can be killed instantly by the crowing of a rooster, and their powers don't work on weasels.
In some legends, Basilisks are also weak to themselves. There are stories of men killing a basilisk by wearing mirrors sewn into clothing.
Trolls. Yeah, they can rip you limb from limb with their bare hands, but a little sunlight turns 'em into inanimate rocks.
One good way to trick a troll into watching the sunrise is to challenge them to a game of riddles: no troll can resist such a challenge. But beware—according to the legends trolls are extremely good at riddles, and if you decide to give up before dawn then they celebrate their victory by eating the loser.
Many of the oldest portrayals of Satan, the ostensible antagonist to God, has him easily outwitted by peasants and driven away by holy symbols (such as a scapular).
Achilles was the greatest of the Greek Heroes. When he was born, his mother dipped his body in the river Styx (or into a fire, depending on which version of the story it is) so that he would be invincible. The only part of him that wasn't affected was his heel, which was where she held him. Given that the trope Achilles' Heel is named after him, you can guess what happened to him eventually. However, some of the myths indicate that he was shot with arrows poisoned with hydra venom, the same ones that killed Hercules, which deflects the weaksauce bit. (If he can only be killed by shooting him in one really hard-to-hit spot with arrows dipped in a poison that, even diluted, could bring down a demigod, then that's... actually a very minor weakness and not weaksauce at all!)
Not even a weakness, really. Just a specific place where he's down to normal human vulnerability.
Homer's depiction of Achilles does not appear to include the tradition of limited invulnerability. When Achilles takes the field in the later books of The Iliad, a spear (thrown by a mid-level mook) grazes his shoulder and draws blood.
In folk tradition, salt is often used to repel evil. It was said a circle of salt could protect one from witches, that salt over your doorstep would ward off ghosts and evil spirit. Salt was often seen as a symbol of purity, especially in its uses: Salt is a conservation agent after all, and salt-cured meats don't spoil. Salt as a purifier appears in Shinto (Where it is used as a ritual purifier and small mounds of salt can be used to repel evil spirits) and Christianity (where it is used before mass and to consecrate a church).
In Arabic legend, a ghoul could be killed with a single kick. However, there's an up-side—kick the ghoul again and it immediately springs back to life.
Kappa in Japanese myth are river goblins ranging from mischievous to outright malicious who are said to kidnap children to drown them or tear out their souls and livers. They have a dent in their skulls in which they store water, allowing them to walk on land. Despite their appearance, kappa are extremely well-mannered and cannot resist answering a polite bow with an even deeper one. This will cause the water to spill from their heads, forcing them to retreat. Additionally, they love cucumbers even more than children and can easily be distracted with them.
Tobor, the 8th Man, recharged his powers with an inhalant stored in small, thin, white tubes that he carried in a cigarette case. When the bad guys allowed him "one last smoke" before executing him, this was great; when he was having a fight where kids could see him, he worried about setting a bad example by appearing to smoke.
Vampires In JoJo's Bizarre Adventure are seen as nearly invincible gods among men...unless the sun is out. Or you punch them with sunlight-infused martial arts. Or you hit them really hard in the brain and screw up their ability to control their own bodily functions (though not many beings out there aren't immune to that). Or just have a Pillar Man (essentially super vampires) so much as touch them, which will cause them to be instantly absorbed.
In One Piece, anyone who's eaten a Devil Fruit gets amazing powers, but they all share one weakness; the inability to swim. At all. If they are so much as half-submerged in water of any kind, they become paralyzed (and for many, their powers stop working). Which is kind of a problem, seeing as how many of the encountered Devil Fruit users are pirates or marines in a world that's ninety percent ocean.
Though this is more of a subversion in that this weakness very, very rarely becomes an issue, especially considering how many Devil Fruit users are in the series and how four of them are in the main cast. This is even lampshaded in the Enies Lobby arc; when two members of CP9 are trying to decide whether or not to eat Devil Fruits that had been provided to them, Rob Lucci mentions that being unable to swim isn't much of a problem(then again, all members of CP9 have the ability to Double Jump, so there's that).
Depending on the situation, basic hypnosis (such as Jango's ring or Ms. Goldenweek's emotion-altering paint) serves as one of the weaknesses for Monkey D. Luffy, the protagonist. Due to his simple-minded nature, he just won't have the sense to turn away, which makes him helpless and left to the devices of his enemies.
Water is actually a much greater weakness to Sir Crocodile, as he is a man who can turn into sand; if water strikes him, the sand "sticks together," and he is rendered unable to turn into sand at all, thus leaving him fully open to attack. He has a natural defense in that his sand powers extend to causing alarmingly fast dehydration with direct skin contact. In addition, he has the good sense to not only do his villainous business on a relatively large island, but on a desert island.
And to use the Dance Powder, not only to frame the king in an effort to overthrow him, but also to stop it from raining in the town he was using as a base.
In addition, on the off-chance that someone was able to negate his logia defense for a significant period time (like with Luffy), he's skilled in other combat arts as well. His hook has a second, poisoned hook under it, and if that hook gets broken, he can eject a knife in its place.
Blackbeard has one of the most powerful abilities in universe. He can wipe out entire towns in seconds, shoot the debris out like cannon, and negate Devil Fruit powers. But he can't dodge anything. While most Logia-fruit users can have attacks pass right through them, Blackbeard is quite the opposite, making any physical attack super-effective. Basically increased pain without the ability to die, like getting stabbed with fire.
The specialists, the Paper Sisters in Read Or Dream can telekinetically manipulate paper... unless it's wet. This was not a weakness for Yomiko Readman, who is shown on camera manipulating paper while underwater. This is actually explained in-universe. The Paper Sisters' powers are essentially imperfect clones of Yomiko's, artificially created by Dokusensha; which is why they are weaker and more specialized/limited. Water naturally disrupts the structural integrity of paper, and their inferior powers are not sufficient to maintain it the way Yomiko can.
Super Dimension Fortress Macross has an alien attack force made up of gigantic Scary Dogmatic Aliens who are a proud warrior race do a mass Mook-Face Turn because of... singing. And souvenirs. In fairness, it does make sense in the story (at least as much as The War of the Worlds Martian's being vulnerable to Earth's diseases) and is perhaps one of the best logical conclusions to a typical alien's Planet of Hats treatment. The aliens have no culture to speak of other than fighting, so when exposed to humans and their culture in the form of songs and interacting with the other gender after sending a team of spies to the SDF-1, typical Zentradi start feeling emotions, questioning their purpose, and becoming similar to humans. Because of this, their entire fleet gets deemed "contaminated" by the unexposed Zentradi and programmed for destruction. In the face of this Enemy Civil War, they wisely choose to ally with the humans. Still, it doesn't quite wash away the faint air of ridiculousness when Minmay's singing becomes an offensive weapon to unbalance the unexposed Zentradi in their attack.
Taken to even greater extremes in Macross 7 where the spirit draining Protodevilins's only weakness is actually the energy produced by music. It produces a spiritual energy "too pure for them to absorb" and regenerates the lost energy in those drained by them.
In one humorous scene in Macross 7, a Protodeviln gets a "brilliant idea" for shielding himself against the humans' singing. He puts on earplugs. This actually does work, but Basara just plays even louder. Afterward the Protodeviln installed a noise canceller in his mech, which proved much more effective.
The use of Minmei's voice as a weapon is actually short-lived: while the Zentradi were initially too distracted to react, as soon as the heroes opened fire they started firing back. The real decisive weapon in that engagement was Minmei kissing Kaifun: the Zentradi were so disgusted they stopped fighting effectively, trying absolutely anything to erase the image from their minds, including firing in the middle of nowhere (a Zentradi heavy cruiser was observed doing exactly this as Hikaru locked his nukes on it) and listening Minmei's songs. Incidentally, Macross 7 shows us that Minmei's registered songs have absolutely no effect on unexposed Meltrandi (the FEMALE Zentradi) that just ignore them (partly because they had the common sense to just jam the frequencies used to broadcast them), but BASARA's songs made them groupies the very moment he managed to get them to hear him. It baffled a UN Spacy higher up, who had assumed the Meltrandi would just jam the broadcast (both times the Minmei tactic had been seen used had been with broadcasts the enemy didn't jam for a reason or the other).
They could also be paralyzed by kissing.
In Rosario + Vampire, vampires are considered the high end of the monster scale, but the fact that you can take a vampire down with a glass of water kinda puts a dampener on that idea. Though, you'd have to be of werewolf speed to even consider hitting them with the stuff in the first place.
Vampires are ironically said to have the most weaknesses compared to any other monster. Things like silver would also do them in.
The titular hero(ine) of Ranma ˝ can be incapacitated by the mere sight of a cute little kitten. However, those who attempt this should note to apply said weakness quickly and forcefully — prolonged, intense exposure has a tendency to backfire. Thanks to his Gender Bender curse, cold water can also count as a weakness. Technically. Ranma's female form has less strength and reach than his male form (though the anime is explicit that Ranma's speed is boosted in this form, so it's more of a trade), but s/he can still pull off all of his/her normal attacks. Based on a character with an identical curse, it's also possible that being in female form weakens his Ki Attacks.
His fianceeShampoo and his main rival Ryoga Hibiki have an even worse case of the water weakness than Ranma does; Jusenkyo made them become a little kitten and miniature pig respectively when splashed with cold water. So they go from incredibly powerful fighters to harmless little animals whose only recourse is to run or hide until they can get some hot water. Genma Saotome, Ranma's father, subverts it; his panda form loses little, if any, speed and agility while gaining in strength and toughness due to the increased bulk. Mousse, meanwhile, seesaws between subverting this trope and playing it straight with his duck curse; while it is much smaller, weaker and can't use his physical attacks, it can fly and he's still capable of throwing barrages of knives, darts and bombs in it.
And a non-water version applies to Happosai, who is such a Dirty Old Man that his perversion becomes his own Achilles heel. If there is a fight serious enough, or a reward great enough, that he can't be immediately distracted from whatever he was doing by the sight of girls in skimpy clothing, bare cleavage or a bra, it hasn't come up in the series. He can even be lured right into dangers simply by tossing a bra in the right place.
Spoiled Prince Saffron has incredible fire magic powers, the ability to fly and regenerate so fast that he can tear off his own wings to use as throwing weapons and grow them back in seconds, but because of his lax and pampered upbringing he can't take any sort of physical blow and in a world full of martial artists that's a big problem
This motion sickness seems to extend to being carried by people, as well. He's perfectly fine being taken to flight by Happy the cat, however, reasoning that Happy isn't a vehicle.
According to Rogue, all Dragon Slayers suffer from this.
Wendy however, doesn't suffer from transportation. Rather, She's weak to pickled plums.
In Bleach, Espada #9 Aaroniero can't use his shapeshifting when in sunlight. Though he can still use any of his other 30,000+ powers (not that he does before getting killed, but he had the option).
To make matters worse, he lives in Hueco Mundo, which has no natural sun. His boss builds a fake one for no discernible reason.
Fullmetal Alchemist: In the manga and second anime, Pride can project razor-sharp tentacle-like shadows from his body. But he can only project them where ordinary shadows could be cast; complete darkness renders him unable to attack and bright lights can cut off his tentacles. Granted, he is still near immortal even when he can't attack; in a way he is both the most powerful and the most vulnerable homunculus.
A common mistake for people in the series is to assume that Flame Alchemist Roy Mustang is useless when wet (or without his gloves). This is only true to a certain extent (he's arguably more dangerous with lots of water around, as he can spit the water into hydrogen and oxygen and then ignite it...the problem is that unless he can trap the target in an enclosed area with the water he's liable to blow up any nearby allies and himself at the same time, hence this technique being very rarely used), and let's just say he earned his rank.
A combination of this and Berserk Button: Insulting Ed's height, while entertaining, has a tendency to impair his judgement as he blindly charges the enemy. This is mostly Played for Laughs, although Pride uses it once to get an edge in combat.
Pride: Appearances can often be deceiving. Isn't that right, little alchemist?
In Naruto, Konan of the Akatsuki is, like all members of that group, very powerful. Yet her paper-based techniques can be completely nullified by spraying oil on her to make her stick together (a technique one human ninja and some summoned toads have), although water can release her.
Adam Blade from NEEDLESS has a weakness for little girls, and usually ended up getting his butt kicked because of this. Though later in the manga his weakness had developed from mere lolis to naked lolis. In the other hand, his love for lolis can temporally boost his strength and saves him from a Lotus-Eater Machine, so it's subverted.
Emperor Nightmare, the leader of Nightmare Enterprises (Holy Nightmare Co. in the Japanese version) in Kirby: Right Back at Ya!, is weak against AND afraid of one weapon that Kirby can take control of by swallowing his Warp Star: the Star Rod.
Nightmare: Aaaah! How did Kirby discover the secret?! That pitiful little Star Warrior has found my only weakness! I am helpless against the power of the Star Rod! WAAAAUUUUGGGGHHH!!!!
The Dai Gurren in Tengen Toppa Gurren Lagann is a walking battleship...that is not designed to go on water. A battleship that isn't designed to go on water.
Apparently, whistling around Piccolo, or any Namek can really incapacitate them. This becomes a plot point in the DBZ movie Lord Slug where Piccolo asks Gohan to start whistling after ripping off his own ears in a desperate attempt to stop Lord Slug.
In the manga Fukashigi Philia, the villain Shidow is extremely fearful towards water to the point if he gets in contact with it, he will go berserk and have his abilities neutralized.
All of the Abilities Users created by Noa and Isumi have a particular weakness - it's usually whatever originally killed them (such as water for Shidow, who drowned, or dry ice for another, who froze to death).
Kinnikuman is weakened by milk. Though after he goes insane during his match against Curry Cook and drinks the stuff, it becomes apparent that he just thinks it's disgusting.
Fairies from Jinrui wa Suitai Shimashita are killed by EM waves, a.k.a. light, the most ubiquitous thing in the universe. If the setting wasn't After the End they'd be screwed. And they still have problems with it anyway.
Shiina from Angel Beats! is Ranma turned Up to Eleven: a ridiculously hypercompetent ninja, but when she sees a puppy about to go over a waterfall she instinctively does a Stupid Sacrifice, getting them both killed...and it was a stuffed puppy. The puppy trap was actually meant for Angel, so it's possible she has the same weakness.
Italy from Axis Powers Hetalia can run insanely fast, and defeated the Ottoman Empire, which was pretty powerful at the time, while he was only a child. According to the author, the only thing keeping him from dominating Europe is that he's just too afraid to.
Almost every Green Lantern from The Silver Age of Comic Books onward had yellow as his main weakness. Any criminal could waltz past him by wearing a yellow suit and stealing only gold, and shoot yellow painted bullets from gold plated guns. That being said, a clever person could find a way around it. Such as using the ring to pick up something not made of yellow, and hitting the criminal with it. There have been various explanations such as programming bugs or a deliberately-induced Fantastic Fragility, but the currently-accepted explanation is a combination of yellow representing fear, the enemy of the Heroic Willpower energy the Lanterns wield, and the fact that a yellow fear monster had been imprisoned in the Central Battery, tainting the power source. The weakness can now be recognized and overcome, and adaptations tend to downplay it into almost nothing.
Frank Miller parodied this in All-Star Batman & Robin The Boy Wonder. Before confronting Green Lantern, Batman and Robin paint a house, and everything in it, yellow. Then they put on yellow costumes. Then they paint their exposed faces yellow. When GL comes over, Batman goes so far as to offer him a nice refreshing glass of lemonade, while Robin eats some lemon ice cream. Hal was not amused. Readers were.
The original Green Lantern was almost as bad — his weakness was wood. Since so few people knew it as later Green Lanterns became famous, however, he in many cases seemed more powerful than the new Green Lanterns because, for example, the Sinestro Corps yellow power rings couldn't even make him flinch.
This was parodied in the Justice LeagueGolden AgeAffectionate Parody episode "Legends", with his stand-in version "Green Guardsman", who had a weakness to aluminum. Either way, you've got a superhero who could appear on the news after having been beaten to death with a baseball bat — and considering that one of his foes was the Sportsmaster, who did wield a baseball bat... it's pretty darned weaksauce.
It didn't hurt that wood, while very common when Alan Scott first hit the scene, had become rarer in civilization by the time The Silver Age of Comic Books hit. Villains in The DCU tend to decorate in metal, plastic, and Zee Rust by then, which means even less to block that strange ring with.
This actually becomes a problem for him in the Elseworlds story Kingdom Come. Like most of the other original heroes, Green Lantern Alan Scott's powers have progressed to a ludicrous level - he keeps watch over the Earth in a massive emerald Space Station, constructed himself a suit of impressive armor, and carries around a sword made out of pure energy - all from his power ring. None of it helps very much against Green Arrow in the final battle, since this Oliver Queen's arrows are made out of wood.
This was the main reason that Solomon Grundy was such a threat to Alan. Being drowned, soaked in and resurrected in a swamp, his body was filled and covered with plant matter, rendering the ring all but useless in directly affecting Grundy (Swamp Thing even explained that Solomon Grundy was now a plant-based elemental of sorts like he was).
The Elseworlds story Superman & Batman: GenerationsHandwaves the odd Green Lantern weaknesses by having the Guardians explain that all weaknesses are mentally-imposed. Alan was weak to wood because a thug surprised him with a baseball bat and he assumed the ring didn't work against wood, while Hal was told that the rings were ineffective against yellow and thus added the weakness himself. Kyle, who gets his ring without hearing the explanation, lacks any weaknesses. (This is not, to be clear, how it actually works in continuity.)
Another story, detailing the ring's story and Alan Scott's backstory (for readers in The Nineties, at least), the guardians, in a long story involving one of Earth's first Green Lanterns, retcon the weakness. Because he was almost killed by a yellow monster, the weakness was removed from his ring. He became mad with power, so the Guardians gave him the wood weakness so primitive humans could club him to death. However, instead of dying, he put his soul into the power ring and battery, which collided with a Meteorite, becoming the Starheart. Alan Scott got his ring from the Starheart. Seriously.
One Green Lantern story subverts this, however. A yellow robot attacks the Justice League. GL responds by picking up mud from a nearby swamp and dropping it over the robot's body, completely coating it. With the yellow hidden, he quite easily rips it open.
This was a very situational weakness, as sometimes Hal's constructs interacted with Sinestro's yellow ones, creating a blue haze that negated both. Other times, Lanterns responded by using variations of Car Fu with whatever they could throw at an opponent, or even remembering that an opaque construct around a target meant only green light got through — and turning any yellow inside the construct into green due to reflective properties of the color yellow.
And then there's the Blue Lanterns, who are incredibly powerful even by Green Lantern standards, but can't use anything but the bare minimum of their powers unless a Green Lantern is in the vicinity.
According to Word of God from Greg Weisman, Green Lanterns in Young Justicedo not have a weakness to yellow and original Green Lantern Alan Scott did not have a weakness to wood either.
Guy Gardner: You're supposed to be one of the most powerful Lanterns ever, but your ring is vulnerable to wood? What happens if a guy comes at you with a pointy stick?
Alan Scott: The same thing that happens to you if he paints it yellow!
The yellow weakness was used in a clever fashion in "Ganthet's Tale", a Green Lantern graphic novel by Larry Niven and John Byrne. Hal Jordan's opponent in this one was a renegade Guardian, who could wield Green Lantern energy himself. The solution was for Hal to fly away from the Guardian at near-light speed, and while flying fire a bolt of energy from his ring. By the time the energy bolt connected with the Guardian, it red-shifted, its visible light wavelengths compressing down the color scale, from green to yellow.
Echo from Daredevil and New Avengers possesses photographic muscle reflexes which makes her nearly unbeatable in hand-to-hand combat. She's also deaf, which means she is unable to hear her opponents. Daredevil takes advantage of this by fighting her in a locked, darkened room, rendering her helpless.
One version of Ocean Master, Aquaman's arch nemesis, gets his powers from a magical trident he traded his soul for, and when he isn't holding it he feels intense pain. Even The Joker finds this funny:
"Sounds like the deal of the century, Flipper! And everyone says I'm the crazy-"
In the earlier Aquaman comics, the King of the Sea himself, for all his prowess in the ocean, could not be out of the water for more than an hour or he'd dry out and die. He probably got this from Namor the Sub-Mariner, whom he was initially a Captain Ersatz of.
Aqualad has a less-extreme version of this weakness in Young Justice. There isn't any set time limit, but he succumbs to exhaustion and dehydration far quicker than his teammates after they get lost in the desert.
Power Girl went through a single-issue Dork Age where she could be hurt by any "natural, unprocessed material", including the proverbial sticks and stones. This for a character who's on par with Superman. The negative reaction from readers caused it to never appear again. It was just that weak.
During her JLE days she was also allergic to diet soda, causing fits of anger.
The suit's ability to be torn seems to fluctuate with Empowered's confidence level. Since she has zero self-confidence anyway and the regular humiliations related to her crappy suit only compound them, it is very rare that she has the confidence to use her powers properly. But when she does, she's a one-woman army.
Emp doesn't get the distinction of the weakest-sauce weakness, either... That honor goes to The Lash, a supervillain with a debilitating phobia of fabric stores due to childhood trauma. (He likens it to being put in a sensory deprivation tank.) Also, while not a weakness per se, on two separate occasions a supervillain has shown themselves to be unable to tie a knot, which is a vital career skill in this setting.
Think about it. Being the only villain in the world not being able to tie up the one superhero with a reputation for always ending up bound and gagged by the lowliest of thugs.
The Daxamites in The DCU are almost exactly like Kryptonians when under a yellow sun. However, exposure to lead is fatal to them, even in trace amounts, and (especially true in the Silver Age) being moved away from lead doesn't cure them. Once the poison is in their system, it's not going anywhere. A notable instance of this example was when one of Superman's recurrent enemies/reluctant allies, Paragon, took out three Daxamites with a machine gun while they were distracted by their Jerk AssA God Am I power trip.
Brainiac 5 invented a cure for the lead weakness that's been given to both multiple heroic Daxamites and stolen several times by the villainous ones. Apparently dying by being in the mere presence of bullets makes a character less than credible.
Martian Manhunter has a ridiculous amount of powers, yet he had weakness to fire, making it quite easy to disable him. This because he saw his entire family—and species as a whole—die in a psychic plague that manifested itself as fire. He then buried the bodies of everyone on the planet. This makes his pyrophobia a form of post-traumatic stress disorder. The first attempt to remove this weakness accidentally unlocked his Superpowered Evil Side. Though technically, it's not a weakness of fire, it's a fear of fire.
Prism, a member of the X-Men villain group the Marauders, is a truly pitiful example that combines this trope with What Kind of Lame Power Is Heart, Anyway?. His mutant ability is that he is made of a crystal that can absorb and redirect light energy (like a prism) and is no more durable than glass. Yes, he is made of glass. His weaknesses include any sort of impact. Two of his four deaths (yes, he has died often) involve being thrown into a wall and being shattered by bullets.
Thorused to have a debilitating weakness: If he let go of Mjölnir for more than a minute, he turned into doctor Don Blake, who has a crippled leg (and presumably an acid tongue a dry wit), and Mjölnir turns into a walking stick. Basically, House. This was removed years ago, which now makes Thor virtually invulnerable.
Perun from The Ultimates is essentially a Thor wannabe...without the superhuman strength most Asgardians possess. Despite having a powerful hammer similar to Mjölnir, Perun is killed after an enemy sneaks up on him and quietly snaps his neck.
The greater the power, the weaker the sauce! Marvel's latest and most prominent Superman pastiche is The Sentry, a "golden guardian of good" who's as powerful as he lets himself be. However, he's also agoraphobic—he can't stand being outside. If you also so much as remind him of his little Dark Side problem, he'll fly off to Saturn and cry. Or revert to human form. Or, if he's really unlucky, let the Void out—and suddenly things will look a whole lot better for the bad guys.
One fancomic actually has him carrying around his entire living room whenever he wants to go anywhere.
Iron Man once defeated him by forwarding his mail, more or less.
This was once parodied in the British comic, The Beano, in which the character Calamity James is rescued by a superhero and offers him a Jelly Baby by way of thanks. Guess what the hero's one weakness is!
Used hilariously in the animated series, with an episode consisting of Superman using clever and creative ways of exploiting Mr. Mxyzptlk's "weakness", often without having to use any sort of super powers at all.
Post-Crisis it's a self-imposed weakness. In the Silver Age and Bronze Age, it was a natural aspect of fifth dimensional beings that saying their own names backwards sent them home. In the Golden Age, anyone (human or imp) who said Mxyztplk's name backwards would end up in the Fifth Dimension... or the Fifth Dimension attached to Earth-2, anyway.
Mxy's biggest weakness is that he's a gullible idiot.
Venom. Weaknesses? Fire and loud noise. At one point, he's defeated with nothing more than a lighter (which raises the question of why Spider-Man doesn't just carry a $1.98 Bic lighter with him at all times). This varies Depending on the Writer. Carnage shares some of the same weaknesses.
Fan-favorite (yet sadly not used, ever) Toxin, Carnage's "child" however doesn't, what it does have is being very child like, (one point it refused to help it's host because he yelled at it.)
All Symbiotes are vulnerable to intense heat and sound. The amount of their resistance varies depending on the Symbiote in question (Carnage's resistances dwarf Venom's) and, on a more meta-note, as mentioned Depending on the Writer.
Though it's actually justified in that the symbiotes come from a world with no atmosphere, and thus have no natural resistance to extreme temperature or noise because they'd never naturally encounter them. Even a few generations with them around and the weakness is bred away quickly.
Perhaps in response to claims of how silly his weaknesses are, the Ultimate version of Venom lacks the vulnerability to fire and sound. Instead, the only real threat to him is electrocution.
Marvel's Valkyrie, in her early Defender years, was unable to fight against any foe that was feminine, even if she was alien or a robot.
Marvel'sThe Inhumans, genetic superhumans who have advanced technology and a civilization predating regular humans' by millennia, are done in by... pollution and germs.
Static's nemesis Hot-Streak had the ability to conjure powerful fireballs which he could hurl at his opponents. The catch? His powers were friction-based, so he could only use them after running around (albeit at super-speed, which he possessed in his first appearance) and building up heat energy from his feet. Once Static realized this, he simply attacked from behind and immobilized Hot-Streak with metal fixtures from a playground, rendering him completely helpless.
He was a much bigger threat in the cartoon adaptation precisely because the writers ditched the friction weakness.
Static himself gets completely shorted out if he is hit with water while powered up. He doesn't have this weakness in the comics.
The DCU also had Firestorm, whose weakness is organic materials. All of them. He can't affect them with his power, or he'll suffer painful consequences. So...he could be foiled by a stick. Or a leather wallet.
Firestorm needs to merge with someone in order to use his powers. If the merge happens too long, his powers eat his partner.
In one of his appearances on Super Friends, he was rendered helpless after being sprayed with plant food. Even their version of Aquaman wasn't as lame.
In Firestorm's case, his weakness was probably imposed to prevent the implications of his powers being used on living people and animals. Since Blackest Night eventually provided us with a very memorable example of just how scary his powers could actually be, maybe it was for the best that writers watered him down early on.
Commentators both in-universe and out have pointed out that Firestorm's real weakness is being an idiot. He can simply turn the air around someone to steel, yet his infamously lame villains have included a powerless albino dwarf and a guy with a rope.
The short-lived hero Gunfire had the power to turn anything into a gun by charging it with explosive energy. Anything (except, oddly enough, an actual gun). Enter the Hitman story where Tommy defeats a future version of Gunfire by causing him to turn his own ass into a living grenade. Good times were had by all.
Although it's since been removed, Eclipso - DC's god of darkness - could be dispelled from his human host by a camera flash.
Gladiator,Praetor of the Shi'ar Imperial Guard. Strong enough to shatter planets. Able to fly at many times the speed of light. Can withstand the heat of a star or the blast of a supernova. Has Eye Beams of unimaginable heat, and they can see particles on a subatomic level. Truly a being of such infinite power can only be defeated by...making him feel bad about himself.
Somewhat justified in that his powers are explicitly psionic/mental in nature. If he believes that they won't work or that he can't complete a task with them, they won't work and he won't be able to complete that task. This means you don't actually need a weapon powerful enough to beat him, only something which you can convince him is a weapon powerful enough to beat him, which Rocket Raccoon exploited.
Alternatively, bringing anything to the table that can disrupt psionic powers works just as well, as Nova showed when he beat Xenith -another Strontian- in just one punch after messing up her psionic powers with a headbutt from his psionic-dampening helmet.
Another parody—Super-Ace, an alternate Ace Rimmer from a superhero universe appeared in one Red Dwarf Smegazine comic strip. While he had the full array of Flying Brick powers, his one weakness was ... human flesh. So an ordinary Mook could punch him.
Storm, of the X-Men, has complete control of the weather: in practice it gives her flight, superspeed, and the command of electricity, water, cold, and wind. So what's her weakness? Claustrophobia. If a writer wants to take her out of a battle, all they need to do is drop some rubble on her—and sometimes not even that much. In her early years, she had a Heroic BSOD when a villain only mentioned a word that made her think of enclosed spaces. (These days, trying to stick her in an enclosed space just makes her mad.)
The laughably silly Silver Age DC villain Ten-Eyed Man was a guy whose "power" was being able to see through his fingertips. Every single battle involving him ended with him being tricked into grabbing something causing him incapacitating pain.
He was used as a one-shot villain in Batman: The Black Glove and was defeated by throwing shrimp scampi sauce on his hands.
Zatanna is one of the DC Universe's top magic users, but, because she needs to verbalize her spells, she can be rendered helpless if she's made unable to speak, which led to her being frequently (especially in her early days) Bound and Gagged. Recent comics have come up with creative ways to work with this, such as a Batman comic where the Joker shot her in the throat so she couldn't talk, but she managed to write a spell in her blood. Perhaps due to the frequency with which she finds her sorcery rendered useless, Zatanna eventually started working out and taking combat lessons. She was even briefly able to hold her own in a fight against Catwoman after the villainess duct-taped her mouth shut.
Despite having an incredibly powerful sonic scream, gagging Black Canary could effectively disable it, despite the fact the Canary Cry theoretically should be able to break through any cloth. That too, has decreased in recent years, although Deathstroke found an, “interesting” way to silence her in an issue of Green Arrow.
Venus from Agents of Atlas possesses the same above-mentioned gag weakness. Luckily, she also has superhuman strength to compensate, so it takes a pretty powerful opponent to muzzle her in the first place.
Songbird (formerly Screaming Mimi) from Thunderbolts is another vocal-based heroine who is rendered completely useless if she's gagged.
When he first appeared, Loki had one—he couldn't use his powers when wet/in contact with water. Against Thor, who could easily make it rain. No wonder this is ignored now.
His frequent cohort the Enchantress is one of the most powerful sorceresses in the Marvel Universe. Unfortunately, she needs her hands and voice to cast spells most of the time. Sturdy bonds and a gag are enough to do her in, as both the Frost Giants and Doctor Strange's partner Clea have demonstrated several times.
The sword in, umm, The Sword grants whomever touches it serious Super Strength, enough Super Speed to run on water and deflect bullets, and a powerful healing ability that can close gaping chest wounds and reattach limbs. Unfortunately, these only last for as long as the user maintains physical contact. Put it down to eat a sandwich or go to the bathroom and you're mortal again. At one point, protagonist Dara drops in the middle of a super-strength high jump (a natural reaction to being shot) and suddenly finds she's not landing, she's falling. Worse, go too long without touching the sword and any injuries it healed come back all at once.
The first story of the 2011 relaunch of Swamp Thing features a kid villain named William Arcane. William's connection to the forces of Death (or The Rot) allow him to control all dead or decaying matter. This gives him immense power. The only problem is his fatal allergy to chlorophyll.
"The Day Red Turned to Green", in Tales of the Unexpected #85 features giant mushroom-like aliens that can be harmed by anything red. The main character finds one of their "absorbo-sponges" while spelunking and anything red that he passes while carrying it turns green.
Billy Batson/Captain Marvel says "Shazam!," the name of the wizard who granted him his powers, to change between his hero and civilian forms. This isn't really that bad, but his friend Freddy Freeman/Captain Marvel Jr. has to say "Captain Marvel!" to transform—meaning that he not only has to be careful talking to Billy, but he can't even tell people his own code name without becoming powerless. He started going by "CM3" to fix this.
In the first Titans Tomorrow storyline (which featured evil future versions of the Teen Titans), CM 3 can also be depowered when a recording of his voice says "Captain Marvel!". This is played dead straight, as Batman (Tim Drake) uses a recording of CM 3 revealing his secret identity to Tim to shut him down before CM 3 can beat him into the ground.
Pick someone, hero, villain, or somewhere in between with electricity based powers, chances are their weaknesses are, among other things, rubber and water.
Since Superman's powers come from the sun, he will start to lose his powers if deprived of sunlight for days on end. This was a plot point in the Crisis Crossover "The Final Night,'' which involved a monstrous Sun Eater that was, well, eating the sun.
Speaking of Superman, a cover of an underground comix subverted this trope for laughs. You see loads of bullets bouncing off him harmlessly...and a custard pie volley. Granted, it doesn't hurt him either...but his pride.
How do you defeat your own author? Well, if you're a character in You Got HaruhiRolled!, just show him a disgusting Doujinshi. He'll be so Squicked out that he will be unable to resist you forcing him back through the dimensional portal whence he came.
In Christian Humber Reloaded, Vash, a God-Mode Sue with countless superpowers, multiple super modes, and an arsenal of high-tech and legendary weapons, who can take on entire armies and the main villains of several works of fiction without breaking a sweat, is vulnerable to Paralysis, a Useless Useful Spell in RPGs that rarely affects anything stronger than a common enemy.
When the Discworld had a brief and potentially deadly meeting with the Alien Queen, a very improbable Ripley - albeit one working for the Guild of Assassins - realised that a lifeform based on very strong acids could be vanquished by application of drain and toilet cleaner (very strong alkalines). As she put it, simple alchemy: if the brute spits ph1 at me, then I'm jolly well going to respond with lots and lots of lovely ph14. Acid plus alkali equals salt and water, Captain Carrot. Any organic material subjected to caustic potash is reduced to soap. SHE is going to be a puddle of salty soapy water in no seconds nothing!"
Vampires in My Immortal are vulnerable to steak. Early in the fic, the protagonist, herself a vampire, contemplates committing suicide with one she hides in her bedroom.
Films — Animated
The Blue Meanies from Yellow Submarine are repelled by positivity in any form. This doesn't work out so badly, though, since their entire arsenal is built around the proliferation of depression and despair, but it does still leave them vulnerable to music.
This trope appears as a pastiche in Bolt. The titular dog believes he has superpowers because he never leaves the set of a TV show. When he is accidentally shipped across the country his powers "mysteriously" vanish, and he blames the Styrofoam packing peanuts he was shipped with.
Megamind has Metro Man having a weakness to copper (subverted in that it's completely made up by him as a part of his plan to retire). This is even lampshaded by Megamind:
Megamind: Your weakness is copper!? You're kidding, right?
Copper is pretty common, so Megamind really should have realized it was a fake weakness. Especially since he grew up with Metro Man and would have seen him handle things like pennies or batteries.
In The Incredibles, the superheroes of the world were driven into hiding by lawsuits. The creators were deliberately going for a mundane downfall. Then again, it was really the government that was tired of paying the lawsuits and covering for the heroes.
Stitch of Lilo & Stitch is speedy, clever, and able to lift 3000 times his own size... but is too heavy to swim. One reason falling in water is so damaging is that Stitch tends to panic when he's underwater. He eventually starts handle deep water better; one episode of Lilo & Stitch: The Series (the theme of which was conquering your fears) had him fall into a swimming pool, but he manages to keep calm, hold his breath, and climb out without issue.
The aliens in Signs. It's hard to feel threatened (retrospectively) by creatures which will dissolve in an April shower or corrode in a particularly humid breeze. And are completely incapable of breaking down wooden doors.
In Shyamalan's earlier film, Unbreakable, he also used water as a weakness for the main superhero character. In that case, though, it wasn't that he was especially vulnerable to water, but rather he was just as susceptible to drowning as a normal person. If he drank something too quickly he would choke and if he was submerged he would succumb to drowning just like everyone else—though it was theorized that the dense bone and muscle that made him unbreakable also made him unfloatable (or the character simply couldn't swim). There was a complicating factor in the scene where he ends up almost drowning in a swimming pool. He's tangled up in a big piece of fabric, which would give anyone a bad time while in water. It was also a psychological weakness: he had almost drowned once as a child (probably due to the aforementioned bone density), an event so traumatic he blocked it from his memory. That would make anyone nervous around water, even if they couldn't remember why.
Shyamalan probably got the weakness idea for Signs from Invasion of the Saucer Men, whose aliens were melted by light. There is nothing lamer. Especially considering they were done in by the headlights of teenage hot rodders...!
The Bioraptors (also called 'Demons') of Pitch Black had a similar weakness to light. Though this actually worked, as most of the movie was during a solar eclipse and they broke their flashlights. Oddly enough, the creatures are shown moving about in the light, albeit cautiously, before the eclipse. Compare this to later on, when a lighter is enough to make them run away...
Also happens in The Mole People; in which a lost colony of ancient Sumerians living Beneath the Earth had adapted to their lightless conditions to the point where our heroes could kill them with a flashlight.
In the movie version of The Day of the Triffids, the titular monsters were melted by sea water. Nearly as lame. In the original novel, ironically, flame-throwers are among the most effective anti-Triffid weapons.
The Tenctonese in Alien Nation (the movie as well as the series) are harmed by salt water. Seawater is like acid to them. They live mostly on the Californian coast; while they do develop a tolerance to it, direct exposure is still harmful to them.
There is a slightly funny moment when the police find the partially-dissolved body of a Newcomer washed up on the beach. When asked how they were able to identify him, they simply shrug and show his soaked wallet. All his clothes were, naturally, fine too.
In the Disney Channel movie Up, Up and Away!, the weakness of the superhero family is aluminum foil. However, it's never made clear if it was just their family or all supers who are vulnerable to foil. Both Spider-Man and Superman are mentioned to exist in this 'verse, and they don't have any weakness to aluminum foil (although Supes has his own weakness). If the weakness is hereditary, then it should realistically only affect one of the parents.
In SYNGENOR, the titular creatures were created to be the perfect soldiers for a war with the Middle East. They don't need to eat or sleep, are immune to most weaponry, and reproduce every twenty-four hours. Their only weakness? Water is like acid to them. It's somewhat hard to be afraid of a super soldier that can be defeated with a super soaker. Or, if worst came to worst, by peeing on them.
In the Dead Gentlemen Productions (of The Gamers fame) running Demon Hunters series, Duamerthrax the Indestructible is a walking brick that is, well, all but indestructible. He's an "earthwalker", a demon said to have been kicked out of hell for being too mean. Unlike other monsters and demons in the mythos, he's not susceptible to ordinary injury. He can eat the round of a large-caliber revolver jammed in his mouth ("Mmm! Nice 'n' leady!") casually regrows limbs after being dismembered, and generally shrugs off what few injuries he even takes while making terrible puns. So what's the convenient balance? We're told that every earthwalker has a weakness to some substance, "a plant, metal, anything". Duamerthrax's turns out to be mint. Being shot repeatedly at close range with numerous handguns does little more than inconvenience him, but the breath of someone having just used breath spray causes him intense pain, water-guns full of mouthwash can inflict serious harm and mint dental floss can do even worse things.
Imhotep in his incomplete form The Mummy Trilogy was immediately chased away when a cat is in his presence, because they guard the Underworld. Naturally, the heroes never did anything to exploit this weakness, such as by putting cats in the room full of the people he needed to kill to stop being vulnerable to cats.
Rendered especially silly by the fact that if you've ever been to Egypt, you'll know that there are stray cats absolutely EVERYWHERE, meaning that all the heroes had to do was go downstairs and grab some.
Rick did place a cat in Evey's room, thought it seems to have slunk away to a corner where it wasn't much use. Still, when Imhotep came to call, all Rick had to do was hold it up in a pseudo-menacing fashion. This was enough to drive Imhotep away. Soon after, the mummy regained his powers completely and lost that particular weakness. This still doesn't explain why the other people he had marked out as victims hadn't kept cats on hand.
From 1966 superhero parody Rat Pfink A Boo Boo: "Remember, Boo Boo, we have only one weakness... bullets."
Like the Dalek example given below, in RoboCop (1987), the killer robot ED-209 chasing the titular character was taken out of play simply by trying to chase RoboCop down stairs that its chicken-walker legs were ill-suited to negotiate.
Derek Zoolander can't turn left until his Big Damn Heroes moment. (Though continuity nitpicks will note that he does turn left (relative to himself, though not the camera) while in disguise while trying to retrieve Maury's computer.)
Mystery Men: Invisible Boy's weakness was anybody looking at him while he was invisible. (Machines, like motion detectors and cameras, didn't trigger this.)
The Super Cop in Super Fuzz has super speed, super strength, invulnerability, telekinesis and so on, but he completely loses his powers when he sees the color red (probably a nod to GL and his vulnerability to yellow): a red traffic light, a red flower, a red ribbon, and he's harmless.
The Psychlo homeworld of Battlefield Earth can be blown to (relatively) tiny bits with a nuclear explosion. You'd think that a nuclear bomb is substantial enough to bypass the Weaksauce bit, but remember that this is a PLANET. It'd be like a human exploding in a smear of gore after stubbing their toe. The given reason is that the planet's atmosphere ignites upon the slightest exposure to radiation. This, of course, implies that the planet completely lacks in any heavy elements.
As is the usual with horror movie monsters, the 1973 Blaxploitation movie titular character Blackenstein was Immune to Bullets, fists, and blunt objects—traits which, when added to his Super Strength, seemingly made him all but unstoppable. What is it that finally laid the mighty monster low? The primal forces of nature themselves or divine intervention? No. The police sicced the hounds on him. That's it. Doberman Pinscher fangs trump bullets, apparently.
Mad Max: Beyond Thunderdome. Blaster is the immense Dragon to Master. According to people who want him dead and have been hunting for the right assassin to get the job done, "He can kill most men with his breath." His weakness: he can't stand high pitched noises. Max discovers this when the car alarm on his vehicle renders Blaster into a writhing, screaming, mess- and promptly figures out that his old police whistle can have the same effect.
The goblins from Troll 2 are defeated when Joshua eats a double-decker bologna sandwich in front of them during the film's climax. They can't come within 20 feet of you after you eat 2 bites of bologna.
Ernest Scared Stupid's titular monsters are these trolls, who legend speaks of them being weak to... milk.
In The Lair of the White Worm, a vampire's natural enemy is the mongoose due to vampires in this universe being snake-people. The mongoose ends up getting killed anyway but it's still enough to make the Big Bad retreat for a while.
Also, playing the bagpipes puts them in a trance. Unless they have earplugs.
In Hook, the Lost Boys exploit Captain Hook's fear of the sound of ticking clocks, which they attribute to Hook's memories of being pursued by a clock-swallowing giant crocodile. Subverted when Peter points out that Hook can't really be afraid of the crocodile, which he killed years ago; rather, Hook is afraid of time, as he's become an old man beneath his wig and make-up, and old age is hardly a fear that can be dismissed as Weaksauce.
Superman IV: The Quest for Peace brings us the horror that is Nuclear Man who, for reasons unknown, is powered solely by the sun. The minute he is out of direct sunlight he stops dead. Even if he's in a well lit room but slightly in the shade then he's next to worthless. This is especially pathetic when you consider that, in canon, Superman's own powers are ultimately derived from sunlight, but *he* doesn't power down in the shade.
In The Traveler, the only way to counter Mr Nobody is actually by letting him hear his real full name, which will make him lose powers and become vulnerable to physical attacks. Kinda makes sense for him to conceal his identity throughout the film.
Played for laughs in Evolution, where the aliens' critical weakness is to dandruff shampoo.
Hancock's only weakness? His real wife. Any attempt to live a loving, fulfilling life with his wife of 3,000 years will cause them to both become mortal in order to die together. Unfortunately, Hancock has a hero complex to save people. Which attracts bad guys who attack them in their weakened state. They argue, he leaves, they meet again and the whole cycle starts again. His wife says the gods who created them gave this as a gift. So that they could find love and be happy, and not have to see everyone they care about die as they remain unchanged and alive.
The almost unknown film ROTOR is about a robotic policeman gone mad. He's almost unstoppable except for being paralyzed by loud noises. This might not sound that dumb until you realize he's repeatedly frozen by people honking their car horns at him or playing a radio a little too loud.
Marcus Wright in Terminator Salvation is every bit as tough and unstoppable as you would expect from a terminator... except for his glaring exposed weakpoint in the form of his organic human heart (which isn't even covered with any sort of armor; it just hangs there in a big gaping hole in his chest, leaving it completely exposed to any stray pistol shot or well-aimed punch).
In Godzilla (2014), Godzilla's arms are very stubby compared to the rest of him. The male M.U.T.O took advantage of this a couple of times by jumping on his head and stabbing away at him with those long forelegs, with Godzilla having an extremely difficult time dislodging him since he could barely touch the top of his head. They are plenty strong, though, and he uses them to fight the female Muto.
The Darklords of the Lone Wolf gamebooks are (were, as of Book 12) crippled by clean air and can only unleash their full strength in toxic habitats. Half the reason they waged a centuries long campaign ruining Magnamund (the other half being that they are Always Chaotic Evil embodiments of evil) is (was) to make the world a paradise for themselves. Even in their weakened state they can still put up a good fight with their mastery of Black Magic and immunity to conventional weapons. In one story arc, the Darklords develop a magical engine that allow them to retain their full strength outside their realm. About a dozen of them are on the frontlines of their war when the protagonist smashes the engine, singlehandedly ending their reign of terror.
In one Choose Your Own Adventure book, The Enchanted Kingdom, your character visits a mystical land populated by fairies. You find out that they have the standard folklore aversion to iron, but when some ghouls break your sword, you find out the ghouls are weakened by the presence of plastic when you pull out the only blade you have left, your Swiss army knife.
The Wicked Witch of the West from the The Wonderful Wizard of Oz was done in by a pail of water. This was explained in the book (but not in the movie) as due to her being "dried up by years of evil" but no indication was ever given that water would kill her. The book does mention that the Witch would never go near Dorothy when she bathed because she hated water.
The Wicked Witch is not the only one afraid of water: while Tin Man doesn't melt, he rusts to the point of total immobility - even though he shouldn't.
Another Oz-related Weaksauce: the Nome King was an extremely powerful, nigh-invincible subterranean fairy who had armies of nomes... all of them, including him, could be weakened to the point of being killed by eggs. This doesn't look as bad as it seems at first, because there's only one chicken in Oz, and even that one was brought there from Kansas.
Tik-Tok is an impressive clockwork man, whose processes (thinking, movement, and speech) are powered by three separate springs which need to be periodically wound, or he'll run down. And he is unable to wind them himself. Leaving him alone for more than a few hours is all it takes.
Wicked, a parallel novel based on The Wonderful Wizard of Oz, explores the Wicked Witch of the West's weakness to its entirety, explaining that since birth, exposing her skin to water hurt her, so she had to clean herself with oil and find creative solutions for things which normally involve using water. When she cries, it's like acid flowing down her face. Weakness to water could be the result of the unexplored concept of being "a daughter of the dragon". Its also implied that if Elphaba had ever come into the fullness of her powers, water would cease to be a true threat to her (at one point she instinctively freezes a lake, allowing her to cross it unharmed). The Musicaladaptation openly mocks the entire idea of water melting the Witch. Elphaba uses this urban legend about herself to fake her own death at Dorothy's hands.
The weakness from The Wonderful Wizard of Oz is spoofed in the Enchanted Forest Chronicles, where evil wizards can be melted with water—but only with soap and lemon juice added. The good witch Morwen, on the other hand, explicitly does not melt. It is later theorized that this might be because the wizards never shower while Morwen is something of a neat-freak. Eventually, the heroes refined this into a one word spell with the same effect. One very memorable word, too: Argelfraster!
The aliens in The War of the Worlds were killed by a common disease. The aliens were so advanced and germophobic that they wiped out all microbial life on their native planet. Which meant they had nothing to develop immunities to when they invaded Earth.
The Boggart in Harry Potter and the Prisoner of Azkaban seems to be almost an incarnation of this trope. A Boggart will materialize in the form of a person's worst fear (though exactly what that means is debatable). The way to repel one is to forcibly imagine the fearsome thing as something ridiculous, and then laugh at it. Alternatively, the Boggart can't handle trying to frighten more than one person at once, as attempts to materialize into more than one person's fear results in things such as the "half a slug" incident. This is why Lupin advised his students not to face a Boggart alone (combined with the above reason).
Pottermore goes a little more into detail with the boggart - since they're nearly impossible to kill and feed off emotion, they're incredibly dangerous to Muggles, but given that Riddikulus is such a simple spell that a thirteen-year-old can learn it in minutes, even a very powerful boggart is a minor nuisance to a prepared wizard. At one point, it describes a boggart that had fed on the fears of local Muggles and become "an elephantine black shadow with glowing white eyes"... only to then note that a Ministry wizard was able to trap it in a matchbox.
Voldemort's inability to understand Love, and The Power of Love, proves to be his ultimate undoing. However, this is more of a Fatal Flaw. Harry does not beat Voldemort because of some mystical aspect of love, but because having reliable friends and allies ultimately gives him an advantage over Voldemort, who underestimates the capacity of others to behave selflessly because he would never even consider doing so himself.
In the Sin War trilogy, Diablo, the Lord of Terror and one of the three most powerful evil things in existence, is defeated by a reflective surface. Diablo appears as things you fear, and if it's bad enough to scare Diablo, it's pretty bad.
Eddings' The Redemption of Althalus featured both one protagonistic and one antagonistic Five-Man Band, both with similar power arrays. The villains included the evil mind-leech Koman, with telepathy and mind-warping abilities... who was defeated when Althalus thought about random numbers. Fractions of numbers, even.
The Auditors in The Science of Discworld III: Darwin's Watch. There are very logical and clearly worked out reasons why chocolate kills them in Thief of Time, due to some peculiar circumstances. In SoDIII, though, it just does.
Non-incarnated Auditors can be killed by getting them to say "I", "me", or otherwise admit individuality. Since it's widelyknown that (a) only living things have individuality, (b) all living things die after some amount of time and (c) any living thing's lifespan is practically no time at all compared to the universe's, any Auditor who admits individuality instantly dies. By the perspective of the rest of them, this isn't much of a loss, since there are more Auditors than there is anything else in the universe and, by definition, any given one of them is supposed to lack any defining characteristics.
Much of the plot of Carpe Jugulum concerns a group of "modern" vampires attempting to subvert this trope by developing resistances to the traditional vampire weaknesses. They ultimately fail to do so.
Discworld vampires play this trope in a weird, All Myths Are True way. ALL weaknesses you might have ever heard of apply to SOME vampire, but you may have to do trial and error to find out which ones apply to the particular one who's trying to eat you right now. There are also a few with psychological problems that compel them to do things that directly address their particular weakness (such as the vampire flash photographer who works for The Truth, who has a weakness to bright light, and the one who worked at such jobs as pencil maker, garlic stacker, and whole-sale holy water clerk).
Discworld bogeymen are incredibly strong, reasonably nasty, and some of them can teleport to some extent. Their vulnerability is that they're ridiculously susceptible to Clap Your Hands If You Believe. If you can get your head under a blanket, then you believe you're safe from the bogeyman and therefore you are. If you can get the bogeyman's head under a blanket, he goes into "existiental shock", since he no longer believes he exists.
In Artemis Fowl, fairy magic can be completely stopped by animal fat. That's right, magic that can make you invisible, hypnotize people, heal nearly anything, and in some cases travel through time can be stopped by lard. Praise the Lard!
Possibly a Logical Weakness instead. Fairy magic is strongly connected to the power of life, so animal fat, as a substance strongly symbolic of death, counters the effects.
Some of the laws that (most) fairies have to adhere to thanks to some very old, powerful magic— the most commonly seen are the Ritual for restoring magic (has to be done with an acorn, at the full moon, under an oak next to a bend in the river... or at least to start with. By the second book that's already been thrown out as mere myth.), the 'fairies cannot enter human houses without permission' rule, and by extension, the 'fairies cannot disobey a direct command given by a human eye to eye' rule. These are handwaved away by No1 in the 6th book.
The Haunter in the Dark, the titular monster in a story by H.P. Lovecraft, is an avatar of the god Nyarlatothep. It's a huge winged and tentacled mass of darkness with a three-lobed burning eye, whose touch will burn the flesh from your bones. However, it's extremely vulnerable to light. Even little light will hurt it, and strong light will banish it. So you can temporarily defeat an avatar of an ancient and evil god with a flashlight!. Temporarily. As soon as the lights are out, it can come back, just as nasty as before.
In Worldwar, the invading reptilian aliens called 'The Race' had an immense weakness to ... ginger. Not only was it an incredibly addictive narcotic, but it also made the females produce sexual pheromones outside of the normal fertility cycles, turning exposed members of The Race into crackheaded sex fiends. When the humans attacked Race-occupied Australia, they used missiles armed with warheads packed with powdered ginger.
Even before they discover ginger's effect on the Race females, they find that not only does is it extremely addictive to the lizards, but it also causes them to temporarily feel nigh-invincible - not a good trait for an infantryman, a tank crew commander, or a fighter jet pilot.
In L.J. Smith'sNight of the Solstice series the Fair Folk-like race known as the Quislai have many advantages, such as immortality, invulnerability, extreme beauty, the ability to throw lightning bolts, the power to travel to places quickly using secret pathways through space, and freedom from nearly all physical limitations. They can't be imprisoned by normal means, as doors and windows will unlock themselves for Quislai, and they can travel through dimensional gateways between worlds without preparation while everyone else requires a special magical amulet to use them. However, the one thing that can restrain them is a thornbranch tangled in the hair. Unfortunately, most Quislai seem too ditzy to think of cutting their hair short or at least avoiding rosebushes.
Judges 1:19 is often taken by unbelievers and skeptics to argue that iron chariots are a weakness of God; as the King James Version translates it, it reads "And the Lord was with Judah; and he drave out the inhabitants of the mountain; but could not drive out the inhabitants of the valley, because they had chariots of iron." Needless to say, this interpretation is not generally accepted by believers.
The great Samson got his Super Strength from Nazirite rituals, and breaking them was his big weakness. He attempted to mask this by making up a bunch of equally weaksauce fake weaknesses, only to kill anyone who actually tried them. He was still stupid enough to tell his true weakness to Delilah, despite her being the only one who knew of his "weaknesses" and therefore the only one who could have told them to his enemies. By the time he'd cut his hair (famously thought to be his sole weakness), he'd already violated other parts of the Nazirite rituals, such as drinking alcohol and handling dead bodies. Cutting his hair was the last straw, so to speak.
The Death World creatures of Fragment are averse to salt water and avoid it (it's toxic to them for some reason), which is presumably what's kept them confined to Henders Isle. This is discovered accidentally by a lucky fool who blunders into a saltwater pool while fleeing the orgy of death chasing him, and is later adapted as a defensive measure against Henders creatures.
The main weakness of vampires in Peter Watts's Blindsight-verse is geometry. If right angles take up too much of their visual field, they have massive, frequently fatal seizures. Right angles are very rare in nature, but once humanity developed architecture the vampires went extinct until later humans reconstructed them and developed "anti-Euclidean" drugs to counter the special vampire weakness (and keep the vampires dependent).
In Fred Saberhagen's Book of Swords and Books of Lost Swords series, Shieldbreaker, the Sword of Force, can defeat any weapon, and as such is the only thing that can defeat, even destroy, one of the other Swords, but is powerless against an unarmed man. In the final novel, Shieldbreaker is destroyed by Woundhealer, the only one of the Swords which cannot be used as a weapon.
In The Wheel of Time, channelers are people and therefore are vulnerable to all the things that squishy humans are (though they can do things to help offset that). However, they are particularly vulnerable to Forkroot tea. In normal humans, it's harmless, if at most a mild sedative. In channelers it cuts off their ability to use their magic and knocks them out.
Not to mention that of those who naturally develop the ability to use the local flavor of magic have a 75% chance of it being fatal without instruction.
Trollocs and Myrddraal (the local flavor of evil Mooks and Lieutenants) have the old folk story weakness of not being able to cross running water. Myrddraal, with sufficient coaxing, could drive Trollocs to cross water, but it needed a damn good reason.
In Bystander Lucretcia won the Superpower Lottery. But, she has two big weaknesses. First, she is weak against hot weather. A warm summer day means she can't leave the air-conditioned car, or she'll blister instantly. Two, she sucks at using her powers. Especially fighting. Being as strong as Superman isn't much use when you can't HIT the opponent!
The kids in "How To Kill A Monster" have to figure out exactly how to do that. Falling three stories doesn't stop him nor does poisoning a pie. Luckily, there's a Deus ex Machina way out. the monster dies after they confirm they're humans, as he's allergic.
In "Attack of the Mutant", there's a subversion of the trope that's invoked to then play the trope straight. Specifically, the young male protagonist is facing an enemy supervillain who has the ability to change into anyone and anything. The boy knows in advance that if the supervillain were to change into a liquid, he'd get stuck that way and be defeated, which is the supervillain's Weaksauce Weakness. Since the villain is under the impression that the boy is a superhero, the boy pretends that his Weaksauce Weakness is that he's vulnerable to acid. So the supervillain changes into a wave of acid, and after the boy hastily jumps out of the way, the supervillain gets stuck in his liquid-acid form, thus ensuring his defeat.
Iron against the chaos mages in the Saga of Recluce. Even the strongest bolt of chaos fire can be stopped cold by a thin sheet of iron, and the more powerful a chaos mage is the more they're hurt by iron, to the point that what for anyone else would be Only a Flesh Wound will be a One-Hit Kill for an experienced chaos mage.
Bram Stoker's Dracula averts most of the popular traditional weaknesses; for example, he can't be killed by most conventional means, and can use his shapeshifting powers during dawn, noon, and dusk. However, he does have unique weaknesses; he can only cross running water during high or low tide (this amounts to 12 hours and 25 minutes per day), needs to keep a small amount of Transylvanian soil in his home, and needs to be invited inside before he can enter a building (considering this is Victorian era England and he is a noble, this is a non-matter).
Mercedes Lackey has fun playing with the iron weakness of fae; in her SERRAted Edge book series, the good elves not only use their skills as race car mechanics to work up a tolerance to iron, but also gladly use the metal to shield themselves from enemy elf attacks. Also, elf magic goes haywire in the presence of iron.
In fact, the good elves have noticed that iron makes their magic go haywire in extremely predictable and repeatable ways, so they have incorporated it into their defenses and can use it to, for example, negate their enemies' magic while delivering their own with deadly accuracy.
In the same series, however, she plays the Trope straight in that her elves have a powerful vulnerability to caffeine.
The Hunter from the Coldfire Trilogy is one of the most powerful beings in the series, but also fatally flawed in his nature. As part of his Deal with the Devil to stave off death, the Hunter surrendered his power over life, creation, and light. He can no longer use healing magic without dying, sunlight burns him horribly, and he is completely unable to manipulate ordinary fire. A villain in the first book took advantage of these weaknesses by luring him into a cave filled with crystal and used a mirror to reflect what little sunlight there was back at him, with the light magnified by the crystal. Then he was rendered helpless by being placed in an ordinary bonfire.
Animorphs has one book where the group finds out the Yeerks' Bizarre Alien Biology allows both them and the hosts to treat instant maple oatmeal as an addictive drug on par with heroin. While they plan on dumping a bunch of Quaker Oats' finest into the pool the Yeerks use to rejuvenate, they don't end up using it as a weapon because it plays merry hell on the hosts as well.
In the Codex Alera, all of the various crafters' fury-granted Elemental Powers can be countered by their opposing element (i.e. dripping water on a firecrafter prevents use of fire furies, putting a woodcrafter in a metal cage nullifies wood furies, etc). Windcrafters have greater difficulty using their wind furies closer to earth, and being covered or surrounded by earth renders their furies impotent. However, they also have another weakness: salt, when it comes into contact with their furies, causes them great pain and disrupts them. As a result, anyone expecting to fight a windcrafter carries bags of salt with them to disrupt their Bullet Time, flight, and other powers. Salt-tipped arrows are a specialist weapon against hostile wind furies, and a salt-tipped arrow is what Bernard uses to critically injure High Lord Kalarus in Cursor's Fury by disrupting his wind furies in mid-flight, causing him to take a nasty plummet into a forest and introducing him to Newton's laws in a most painful and crippling manner.
All illusion has the problem that anyone capable of using the Sight can simply activate it and no matter how skilled the illusionist, they'll be able to see what's really going on. While most people avoid using the Sight due to the potential for seeing disturbing, unforgettable things with it, the ability for the most marginally skilled caster to counteract any illusion means that the Council doesn't consider it an especially useful discipline.
Of course, the Sight has it's own odd weakness included in the form of permanent and perfect recall of whatever you see. Sounds good until you remember that normally scary things get the terror factor turned up to 11 and you have to relive it every time you think about it.
All Fae are vulnerable to iron. So much so that Queen Mab, one of the most powerful beings in existence, is scared of an iron nail. The Summer and Winter Knights, while human, inherit this weakness as well- touching iron completely nullifies all of their Fae powers, which is especially dangerous because one of those powers is the ability to ignore disabling injuries.
The Nazgűl from The Lord of the Rings are vulnerable to sunlight and fire, and will not cross running water if they can at all avoid it. The first two are actually a Logical Weakness- as creatures of darkness and cold; it makes perfect sense that they wouldn't like light and heat - but Tolkien never explains (either in the books themselves or Word of God) why they feared water.
Tolkien was famous for using existing legends to establish the reason why certain myths are the way they are. The fact that they fear running water is a reference to many mythic demons, who could not cross running water. In-universe, one could infer that it's because their cloaked robes are the only things keeping their wraith-forms contained in any semblance of physical form. Trying to cross rapidly moving water would run the risk of their cloaks being swept away, meaning they'd become intangible and useless until they found replacement clothing to allow them to reconstitute themselves, which is exactly what happened to the ones caught in the flood outside Rivendell. (This also gives them a second reason to want to avoid fire)
An alternate explanation would be that running water carries the power of Ulmo, the Lord of Waters and one of the most potent Valar. Since things symbolically connected to the other powerful Valar (eagles, the distilled starlight in Galadriel's phial, etc) have been shown to oppose creatures of evil, there is some logic behind this.
The Witch King of Angmar, the most powerful of the Nazgűl and Sauron's Dragon, cannot be killed by the hands of men. This invulnerability does not include women or hobbits, so the lord of Nazgűl falls to the blades of Eowyn and Merry, a woman and a hobbit respectively.
In the first book of Anne McCaffrey's Tower and the Hive series, The Rowannote Technically the second, after To Ride Pegasus, but most fans consider The Rowan the first of the series proper, Prime-level Talents could not travel off-planet, due to Travel Sickness - a severe form of vertigo. They later found out that this wasn't the case - one of their own imprinted her own physical condition on the rest. So now the older Primes consider it a phobia, rather than a medical condition.
A secondary canon Star Trek novel (World Without End) describes Vulcans as being extremely vulnerable to cold, sufficient exposure to Earth's winters can kill them much faster than the exposure can kill a human. When staying on Earth briefly with his mother's family as a boy, Spock has to be completely bundled up whenever he is walking outside in the snow.
The Saurians are immensely strong, can breathe almost anything, have incredible stamina…but being nocturnal and having huge, sensitive eyes, they can be rendered helpless by shining a bright light. Saurians serving in Starfleet wear protective lenses.
In Vadim Panov's Secret City, Nav' are non-agingMagic Knights who will survive anything short of Chunky Salsa Rule. Unless the offending item is made of or covered with obsidian. This was successfully weaponized by both Lyud' in sniper bullets and by Chud' in obsidian sword coatings. The only record of an inter-Nav' war also tells of Nav' warriors wielding obsidian blades.
Leto II, the God Emperor of Dune who lived a few millennia, was vulnerable to water due to his sandtrout symbiosis, which was how he set himself up to be killed.
Grettir of the Old Icelandic The Saga of Grettir the Strong was considered the strongest man on Iceland, but after being cursed by a revenant, he was afraid of the dark for the rest of his life.
The Masters in The Tripods had a huge weakness to alcohol. Granted, so does anyone or anything else that drinks too much of it, but in their case, just a small drink of alcohol-laced water was enough to knock them cold and paralyze them.
The Tanu in Julian May's Saga Of Pliocene Exile are much stronger than humans and can survive being hacked up by bronze swords. However, just a scratch from an iron blade is fatal. Iron is also the only way to safely remove the torcs they use to enslave and/or grant psychic powers to humans; attempting to remove one without iron tools will kill the wearer due to psychic shock.
Epics in The Reckoners Trilogy all have one factor that will at least temporarily negate their powers. They range from incredibly difficult to identify, much less exploit, to ones like ultraviolet light and smoke.
The Parasol Protectorate has the usual weaknesses for vampires, plus a psychic tether to their hive and a strong aversion to citrus that can be overcome with time. Werewolves are vulnerable to sunlight, silver, airsickness, and basil. In this universe, pesto sauce was invented to weaponize the allergies of both species.
Trolls in A Fantasy Attraction has a weakness for... [drumroll] flowers. Herbal shampoo by extension.
In "Rawhide Rex", a short story from Clive Barker's Books of Blood, the titular creature is nearly immortal and capable of paralyzing his enemies with a gaze. What does him in, is his pathological fear of menstruating women. To him, the idea is unnatural and smacks of castration. So strong is his fear, he was able to be entombed in a pit for 400 years simply by being buried with a a few primitive statues depicting a menstruating woman. Having one of these shown to him, makes him seize up in fear allowing the villagers to lynch him to death.
In the Sabina Kane series vampires spontaneously combust when attacked with apple-related substances (some examples: Sabina's apple cider bullets, applewood stakes, and a can of pepper spray loaded with apple cider instead). Justified by vampires' ancestral connection to the Garden of Eden, through their progenitors Lilith and Cain. Sabina, however, is immune, because she's half-mage. Garlic is pointedly harmless; in fact Sabina's Internal Monologue states that the vampires made that up as a smokescreen for the apple thing.
"Truth in Television", or as close as you can get: A book on ghosts states that they actually can't stand salt. If you sprinkle some on your doorstep, they can't get in your house. It's supposed to be pure.
The Fair Folk are also weak against salt, sugar, or any granular substance. If some is spilled, they have to stop and count each piece. After losing a fight against one, Sam simply says "Why didn't I do this earlier?" and opens the capsule of salt he had on him.
For some reason the Leviathans are harmed by borax, a chemical you can find under the kitchen sink.
Interestingly, this might be one of the reasons why the Leviathans targeted America first, since Borax is also used as a common food additive in every country except America. So in other words, the rest of the world is literallyToo Spicy for Yog Sothoth!
Doctor Who is renowned for ending its episodes either by Reversing The Polarity or exploiting the latest Monster of the Week's Weaksauce Weakness. The most famous example is the Cybermen and their allergy to gold, which underwent a Power Creep, Power Seep, slowly going from "gold dust can gum up the works" to "touch gold, die screaming." It eventually led to Silver Nemesis and the hilarious scene of Cybermen being stopped by gold coins and a slingshot. At the time a popular joke was that in their next appearance, just saying the word "gold" to one would kill it. This was quietly ignored in later episodes, since those Cybermen came from an Alternate History (though a Continuity Nod was made in a tie-in website which stated that said Alternate History Cybermen did initially have an "allergy" to gold, but it was eliminated by R&D). No one has actually tried using gold on them yet...
As of Nightmare in Silver it is revealed that the weakness to gold wasn't due to hardware but, somehow, software problems!
The new Cybermen don't have it much better. Their weakness is being given back their emotions; they fry when the humans they're made from enter What Have I Become? mode. The Doctor really hates doing this because it's turning them back into real people who promptly suffer Death by Despair at the horror of their situation. What makes it weaksauce is that it gets easier and easier to do: "emotions removed" seems to mean "everyone's emotions suppressed by a single Emotion Suppress-O-Tron." If you point a sonic screwdriver at the right doohickey in a Cyberman-run facility - and getting into position to do this takes less fuss with each encounter - an entire invasion force winds up clutching its heads and falling dead. At least with the old ones, you'd run out of coins to slingshot eventually.
The Cybermen had a wide variety of one episode weaknesses in the original series including radiation, cold, plastic, bullets (yes, really) and nail varnish remover.
"Image of the Fendahl" had the monsters defeated by rock salt.
Daleks are famed for their inability to climb stairs, though this was never established in the show. However, they could be blinded by obscuring their rather obvious eyestalks, or incapacitated by pushing them over. One '60s story even sees a Dalek defeated by pushing it so it faces a wall and then piling rocks around its base to stop it moving. In their very earliest appearance they could only operate by absorbing static electricity, preventing them from leaving their city. This was later ignored, even in Genesis of the Daleks, which was set earlier. Over time, they became far more credible foes. They were actually shown climbing stairs in 1988's "Remembrance of the Daleks" (much to the Doctor's horror). In the new series, they cannot only hover but swoop around like crazy ("EL-EV-ATE!!"), remove foreign substances from their eyestalk lens (much to Wilfred's chagrin), and incinerate humans on touch. Their main weakness now seems to be stupidity, given that the Doctor convinced them a Jammie Dodger was a TARDIS self-destruct device.
This only worked because the Doctor threatened to "use it" if the Daleks present tried to scan it to verify his claim. Considering Daleks probably haven't got any clue about Earth biscuits, it's more a case of uninformed cautiousness.
The Slitheen, due to their bodies consisting mostly of calcium, messily explode if acetic acid comes into contact with their skin, no matter how little. Cue the squirt guns filled with vinegar.
"The Fires Of Pompeii" has the Doctor fighting seven-foot rock beasts with a water pistol... and winning. Well, irritating them into backing off, not killing them.
The Sensorites from the classic-era first season. Afraid of darkness and loud noises. They panicked if you turned out the lights (we're not talking pitch-black darkness, either - half-lit darkness a person with modest night vision could navigate was enough) and could occasionally be cowed into submission by raising your voice.
"Blink" has creatures that can, when no one's looking, move faster than Jack Harkness confronted with a twelve-step program. When seen, however, they can't move. The episode plays this up for Nightmare Fuel, as you have to blink sometime ... On the other hand, their biggest weakness is being tricked to look at each other.
Apparently, a video recording of an Angel is an Angel in itself. The problem is, if you keep staring at it, it'll eventually download into your brain. That weakness? It's just another trap. Everyone knows to keep their eyes on them, but if you stare into the abyss long enough...
When an episode of Extras featured the filming of a mock Doctor Who episode, this very trend was parodied with a giant slug who was vulnerable to table salt—which he conveniently kept on his desk, just within reach of the Doctor. It's a reference to Colin Baker's first serial, The Twin Dilemma, where the Doctor really does fight a giant slug. In the novelisation, the Doctor briefly wonders where he could find a lot of salt, before dismissing the idea.
The Doctor has one of his own: aspirin.
The Doctor's sonic screwdriver "doesn't do wood" (Hee hee hee!) in that it can't help much against wooden latches and other such things.
It also doesn't do deadlocks, and can be deactivated by some hairdryers.
Sylar of Heroes could be reduced to a writhing, quivering lump with the use of a tuning fork after acquiring Dale's super hearing (though Dale was the same way). This no longer affected him after he lost almost all his powers in the second season.
Similarly, Elle possesses powerful electrical powers, but because of them can be incapacitated by a bucket of water, which shorts the circuit and fries her with her own powers if she tries to use them.
Aquaman's guest appearance explained that he needed to be constantly wet or otherwise have a glass of water or he loses his immense strength and begins to wither. Considering he has had plenty of his own superpowered problems, this is especially glaring.
Kryptonite is so common that Clark would almost be better off powerless. Especially problematic in the earlier years when his "monsters of the week" got their powers FROM kryptonite.
This (unbelievably large amount of Kryptonite on Earth) even made Ultraman flee his own reality because everyone had it and wouldn't hesitate to use it against him.
The classicStar Trek episode "Day of the Dove" features an Energy Being which feeds on negative emotions, and so causes total chaos on the Enterprise by provoking conflict in order to feed on it. Kirk eventually figures out that the alien can be driven off by peace.
In an episode of Star Trek: The Next Generation, the crew deals with a hostile silicon based lifeform that draws its energy from light. They subdue it by turning the ship's interior lighting off.
In another episode the Captain finds an ancient Vulcan artifact believed to be some kind of superweapon. By that time he has realised its critical weakness—it can only kill people who have violent thoughts. Remaining calm renders it ineffective—even Worf is able to counter it using this method. Of course, it's likely that Worf (being raised by humans and tempered by a fatal accident in his youth) is the only Klingon capable of this feat.
In the '80s series V, aliens are vulnerable to certain inoffensive bacteria that live in the human digestive tract. It backfires later on.
The alien "Gua" in First Wave turn out to be badly affected by salt. It affects them roughly like heroin affects humans. One episode featured renegade Gua hiding out in a derelict building snorting packets of McDonald's salt. This is the same series where the hero fought the alien invasion using the lost diaries of Nostradamus, so...
Technically, we never see an actual Gua. They're husks - cloned human/Gua hybrids. it's possible that actual Gua are immune to salt but happen to be crappy genetic engineers.
Nostradamus was actually a psychic alien.
Sportacus, the superhero of LazyTown, becomes helpless if he eats things with sugar, like candy. However it may be that he's actually weak to processed sugar, as he can eat (and in fact gets stronger) from eating fruits, which also contains sugars.
"The enemy of all magic" for the Wizards of Waverly Place is...wait for it...plastic! The villain of the week even manages to take over WizTech by filling the place with plastic balls. Considering how ubiquitous the stuff is in the mortal world, it's a wonder magic works at all. In later seasons, all spells can work through phones. Explain that.
In season one, Kelly can't read minds unless the person is thinking something about her. She advances beyond this weakness by episode 5. But in season 3, her new power rocket science intelligence, is useless because of her "chavvish" personality.
In season one, Simon's invisibility won't work if someone is looking directly at him and he notices. Also in said season, he randomly turns invisible whenever he feels ignored.
In perhaps the most annoying example, Curtis cannot use his time control power at all unless he feels intense regret or fear. This means if someone important dies, he has to either witness it or cause it in order to undo it. It's speculated that he gets over this weakness in episode six of season two. This also happens to be his Berserk Button. He's annoyed by this weakness just as much as we are.
His new power he gained to become a woman, comes with every disadvantage a dirty Hormone-Addled Teenager could come up with.
Then after trading THAT power, he gets the power to resurrect the dead, which seems good, but results in an eventual zombification.
Alisha's weakness is her power itself: people want to have sex with (or rape) her the second they touch her, and don't even remember it afterwards.
Just because he's immortal doesn't mean he can't die first.
A dangerous mind controlling villain cannot control minds unless her victims can hear her.
A shape shifting villain feels incredible pain anytime she shapeshifts.
The new version of the Putty Patrol in season two of Mighty Morphin' Power Rangers were stronger than their predecessors... but the Z logo on their chests is their power source, and hitting it causes them to fly apart. It is also honking big. This rendered the new Putties the weakest grunts ever. In one episode, children (only some of which were de-aged Rangers) dealt with them using a ball.
Rangers had a sister series, VR Troopers that had their own Mooks with a bad weakness. The Skugs could be defeated by touching each other.
In Farscape, Sebaceans are slowly incapacitated by higher temperatures; by higher temperatures, we mean "sweaty but bearable" by human standards. This hits recurring villain Scorpius particularly hard, since as a Scarran/Sebacean hybrid, he has both the crippling heat weakness and glands in his body with no function beyond generating massive quantities of heat, forcing him to insert cooling rods into his brain.
The alien "Frogs" (who despite the name look more like humanoid Energy Beings) in Raumpatrouille are immune to hard vacuum and the beams of the human protagonists' energy weapons pass right through them when they're encountered for the first time on the space station MZ-4 in the pilot episode. What kills them in short order once their unprotected bodies are exposed to it? Oxygen. What keeps this weakness from being completely ridiculous in at least that episode is that they've already vented the station's entire atmosphere into space and wrecked the life support system beyond repair, so the two Orion crewmembers trapped with them have to improvise (and get them all right the first time, too, because the same trick might well not work twice).
In Lost Girl, as a wolf-Fae, Dyson is very strong with excellent senses. These senses can be thrown off by kitty litter. Bo is appropriately incredulous.
The Busters of Tokumei Sentai Go-Busters each have a weak point. Ryuuji (Blue Buster) and Yoko (Yellow Buster) have relatively reasonable and easily dealt with weaknesses, but Hiromu (Red Buster) freezes (to the point of hanging in mid-air) if he gets scared. Which wouldn't be too bad, since he's rather fearless, in general. Unfortunately, he has an extreme phobia of chickens - even seeing a cartoon chicken, or hearing the word is enough to lock him down for a while. This happens in battle multiple times. His Buddy Roid partner, Cheeda Nick also has a terrible sense of direction.
Mythology and Legends
Norse Mythology: When Baldr/Balder, the son of Odin, was born, his mother Frigg made all living things vow not to be able to hurt him. The only living thing that didn't make this promise was mistletoe, which would be fatal to him. So Loki, the trickster god, goes and gets an arrow tipped with poisonous mistletoe and has the blind god Hoor shoot it at Baldr, killing him. Baldr's death would start a chain of events that led to Ragnarok (see further below for the Devil Survivor example).
In Arab folklore, ghouls could be killed with a single kick. However, be careful with the corpse—kicking it again will bring it back to life.
In Rock-Paper-Scissors, Rock's ultimate weakness is Paper (which covers Rock). The other two (Rock breaks Scissors and Scissors cut Paper) at least make sense.
This was mocked in an episode of Corner Gas; Davis chooses rock, while Karen chooses paper. Davis declares he won. When Karen says that paper beats rock, Davis counters with this: if you cover a rock with paper, it's still a rock - you can break a window with it.
It always seemed like Rope (which could suspend Rock) would be a better choice than Paper.
Also mocked in an American commercial where two guys play the game over the last Bud Light. On 3, one guy chooses paper...and the other guy hits him in the head with a rock and takes the beer.
In Monster Bash, you can collect items (bombs) that can be used during each monster, such as garlic for Dracula or a Silver Bullet for the Wolf Man. The Bride of Frankenstein's weakness is a hair dryer.
In Heavy Gear the advanced Black Mamba Gear - one of the more powerful designs in either of the two superpowers' armies - had exceptionally weak rear armour. The result is that Black Mambas could be (and routinely were in gameplay) easily defeated by lightweight Cheetah scout Gears. While the fluff text initially ignored this, the game's designers eventually acknowledged and lampshaded this weakness by having Mamba pilots clamouring for a solution to the "glassback" problem.
Most of the monsters in ''Lucha Libre Hero'' take extra damage from lucha combat maneuvers. And since the PCs are by default technico luchadors, there's a lot of these showing up in the fight scenes. But then, the sourcebook was inspired by Mexican lucha films, and "every problem can be solved with a good wrestling hold" was standard in those films.
In GURPS the disadvantage Supersensitive makes having any other sort of sentient creature with 20 meters a serious weakness. With Combat Paralysis your greatest weakness is being put in any sort of danger. Naturally such disadvantages are not recommended for Player Characters.
d20 Modern has a table of random weaknesses... including some really stupid ones, such as: Clowns, the number 8, math, and books written by William Blake.
In the The Dresden Files RPG, all creatures who take some sort of supernatural toughness, regeneration, or physical immunity must take something called "The Catch", which, when used against them, will take out their ability to shrug off damage. The more common/easily accessible the ability to fulfill "The Catch" (so, something everyone knows about and can get easily), the more points you can get back. So, Catches like "Swords Of The Cross", "Wizards Born Under Special Circumstances", "Soulfire", and "Nuclear Detonations" don't really offset the power, while more common and known substances (like iron vs Fey, holy items vs Black Court Vampires, or physically attacking magically immune creatures with a brick loaded sock) will give you more points to potentially work with.
In Deadlands, there are some creatures and villains who are immune to anything except one weakness. For example, a Hangin' Judge is vulnerable to a weapon held by a legitimate lawman on duty, a Tummy Twister to hot chili peppers, and Jasper Stone to suicide.
That last one is technically correct, but it's so much more. The conditions are actually "Stone can only be killed by a gun fired by his own stone-cold hands", so suicide counts... but so would redirecting his shot before it hit its target. So would having Young Stone and Old Stone shoot each other.
Changeling: The Lost has the concept of "frailties", little weaknesses that certain fae (and overly-powerful changelings) are prey to. Some of them are the classic faerie weaknesses, others can be as odd as "must drink alcohol instead of water" or "cannot cross lines of ants". The only universal weakness is iron, which isn't as dangerous as you think because pure iron is rare... and steel does nothing. These weaknesses differ from subject to subject; the fiction for one book has a Genre Savvy mortal invoking every bane she knows from the old tales in an attempt to scare off one of the Gentry. None of them work.
Rifts has a little fun with the concept of fae weaknesses. Among the ways to protect yourself from Faerie Folk is to turn your clothes inside-out or backwards when traveling through their territory, or by tying colorful ribbons all over you and your gear. But this is less a matter of them being unable to approach you as it is them being too busy laughing to trouble you.
Vampires in Rifts have all the "classic" weaknesses found in folklore; crosses, garlic, wooden stakes, sunlight, as well as a couple usually attributed to other monsters (wolfsbane, silver). One weakness that's rather unique to Rifts, and the most weaksauce of all, is running water, in any form. Which means a vampire that can shrug off nuclear detonations and hails of rail gun bullets can be taken down by a squirt gun.
It's possible to give a character in Champions such a weakness via the Susceptibility Disadvantage. Water, for example, could be worth quite a few points depending on how many dice the character takes from it since it's one of the most common substances in practically any game world. This would make it impossible for your character to do such simple things as bathe or shower, and any kid armed with a Super-Soaker and/or a bucket of water balloons would become a credible threat.
Magic: The Gathering: Marit Lage. An ancient, powerful entity. A sorceress transformed into a horror larger and more powerful than even the mightiest of Eldrazi. Capable of killing a planeswalker in one hit. Immune to most forms of direct damage. And, being a token, is vaporised instantly on contact with Unsummon, a one mana spell that was in more than a dozen core sets.
In Gian-Carlo Menotti's opera Help, Help, the Globolinks, the invading Globolinks are repelled by music.
The Mega Man series has plenty of bosses who had a weakness to unlikely-looking weapons and questionable moves.
The final boss of Mega Man 2 can only be damaged with the most useless and most difficult-to-hit-with weapon, Bubble Lead. The boss is a hologram; other ammo refills its energy (somehow), while the bubble lead shorts it out.
The final form of Wily in Mega Man 3 can be one-shotted with a proper application of Top Spin, a glitchy and hard to aim attack that often damaged you and would drain the entire bar if mistimed. (Thankfully, Search Snakes also work on it—which has much the same movement pattern as the aforementioned Bubble Lead and would be this game's hardest-to-hit-with weapon if not for the Top Spin.)
In Mega Man X and X2, the final boss forms of Sigma were weak against the Rolling Shield (a hard to aim attack that generally did less damage than a charged shot) and the Strike Chain (a pathetically short ranged attack).
Wave Man of Mega Man 5 was essentially vulnerable to being kicked.
This comes up in the series so often that the Genre Savvy veteran of the series will, upon reaching the final boss, immediately switch to the hardest-to-use weapon to try fighting Wily. The cases where this isn't strictly true are Mega Man 1 (Wily is vulnerable to two different Game Breaker strategies), Mega Man 4 (vulnerable to an easy-to-use weapon that is slightly prone to abuse), Mega Man 5, and Mega Man 6 (in addition to fulfilling this trope in those two games, Wily was also vulnerable to Game Breaker Beat, which is why Beat was subsequently nerfed).
Now we have Street Fighter X Mega Man, where one of the weapons is a watermelon. Since this is a Mega Man game, there's going to be somebody from Street Fighter who's weak to it. It's Rose.
In the sequel of the latter game, one of the late game bosses can be one-shot with a specific weapon. Guess who if you know the Shout-Out.
Vampyres in RuneScape avert this somewhat. When they were first introduced, Juvinate or higher ranked vampyres could only be harmed by weapons made of silver.... all of which are weak because silver is a soft metal. So it was more like they were just immortal against everything else, and silver worked as well against them as it did against normal monsters. And then the player learns about the Blisterwood Tree.....
Don't even get us into how this applies to multiple-typed Pokémon.
Poor Shedinja. Its ability, Wonder Guard, is great (invulnerable to all direct damage moves except for the types it's weak against), but it only has one hitpoint, and its type (Bug/Ghost) gives it five weaknesses—including types and common moves that only an idiot would build a team without. That means it's only good against AI opponents that you know don't have those type moves (or any of the environment moves that would defeat it as well). Moreover, while it's invulnerable to direct damage moves, status ailments could affect it normally. Shedinja could simply be confused, and it would effectively commit suicide. Good luck leveling the poor guy without Exp Share.
Inversely, Shedinja is an extremely viable option in the Legendary/Uber arena, in that most of the commonly used Legendary Pokemon have no moves that can penetrate Wonder Guard. For example, the near-almighty Kyogre will be generated most of the time with no powers that can hit Shedinja, letting the tiny bug cut him to death. If you can take out the one or two (at most) Pokemon that could beat Shedinja, you've practically assured yourself a victory.
There's also Paras and Parasect, who in the first generation had threeSuper Effective weaknesses (Parasect is also incredibly slow). One of their new abilities in the fourth generation gives Parasect what is essentially a five fold weakness to Fire. Parasect also gets a 100% accuracy sleep move, which is potentially the most powerful status-inducing move in the game, so this was likely added to keep it from being a Game Breaker.
The Electric type is half-composed of cute little rodents (and a grinning sphere, too, but those are actually dangerous). You'll wind up with one-foot-tall squirrels and mice taking down Gyarados—a 21 foot long sea monster known for destroying entire towns in fits of rage—in one hit.
Several moves and other things introduced in the fourth generation of the games can cause examples of this trope. One of the most hilarious: a Grass-type move called Grass Knot that is said to work by tripping the opponent, and does more damage the heavier the opponent is. The result of this is that the heaviest Pokemon in existence, the Ground-type Groudon, can often be tripped to death in one hit by something as small as a Pichu.
Dragons are weak to Ice-type moves. This means that pseudo-legendaries like Salamence and Garchomp can be taken out in one hit by an Ice Beam from a Cloyster. As of Pokémon X and Y, they're also weak to Fairy-type attacks.
Averted with Kyurem, though, as Ice is its secondary type. As Fire-types resist Ice, too, this also applies to Reshiram. Double Subversion with the aftermentioned Fairy-type, but only for Kyurem.
Double subverted with Kingdra. Due to its Water/Dragon type, the only super-effective type, for a really long time was Dragon-type attacks. note Dragon resists Electric/Grass but is weak to Ice. Water is the other way around. Come Pokémon X and Y, however, and there is the aforementioned Fairy Type. Moreover, there is a certain Ice Type move which subverts the usual type relations, being super-effective against Water (along with Dragon), and therefore opening up a chance for a 4x weakness attack.
Volcarona is widely considered one of the most badass Bug-type Pokemon. It and its pre-evolved form (Larvesta) naturally lose half their health from Stealth Rock. Just from switching in. Same with other Pokemon with double weaknesses to Rock, notoriously Charizard.
All Pokemon that are weak to Water probably count, especially the double-weak ones. Using these critters in battles on the ocean is a common source of head scratching.
Rock/Ground is a common combination. It's double-weak to both Water and Grass, and mons of this type usually have very low Special Defense, so pretty much any attack of these types will be an insta-kill. Ironic, since Rock types are supposed to be difficult to kill. Gen V changed the Sturdy ability to prevent insta-kills, so that they can at least survive with 1 HP and get a chance to attack.
Fairy-types were introduced in Gen VI, and such attacks are super-effective against Fighting, Dark and Dragon types. Hydreigon, Scrafty, and Pangoro thus have a 4x weakness against attacks that typically involve sparkles and cuteness.
While fairies are resistant to most commonly-used types like the ones mentioned above, their counters are Poison(a generally-weak type since Gen 1) and Steel(Lost resistance against Dark and Ghost to adapt being Fairy counters instead of defenders).
Lance, the champion in Pokémon Gold and Silver, is a dragon trainer. That is, he trains dragon-esque Pokémon, not Dragon-type Pokémon. This means all of his Pokémon are part flying, meaning all of them lose at least a quarter of their health to Stealth Rock.
Somewhat in keeping with the game's theme, the Big Bad of Spore, the Grox, is weak against... Life! They can only survive on barren planets; creating a life-sustaining world kills them (although their spaceships can still bomb you from orbit).
Laharl in Disgaea, being a young demon who makes a big deal out of being evil, is violently allergic to women with sexy bodies and expressions of optimism or hope. In one battle he has to fight a bunch of half-naked succubi and nekomata with his stats halved. During one of those chapters, Flonne nearly kills him by yelling "eternal love!" (her favourite words).
This appears to be largely psychological, however. Laharl learns to accept that he is capable of love by the end of the game, and while he makes a few comments about not wanting Jennifer's body near him, her presence has no effect on his stats. In Disgaea Infinite you can even use Mind Control to make him love sexy bodies, and glomp Jennifer.
The novels explained this as the result of being raised by an abusive, buxom aunt. Disgaea D2, however, implies it was because the curvaceous Ranier was his nursemaid growing up, and to get him to sleep she'd smother him into unconsciousness with her considerable...assets.
The fact that the Prinnies explode when thrown is an unfortunate weakness, as well. It doesn't matter how high the level and/or stats of a Prinny is, a simple toss is all it takes to do it in. Unless it's one of those Prinnies...
In the Prinny games, said weakness can be exploited by a Prinny against some particular enemy Prinnies.
In Elite Beat Agents, an alien species known as the "Rhombulans" come to Earth and ban music because they're scared of it. Then the agents come and get everybody in the world to dance to Hoobastank and the Rolling Stones.
Sonicis extremely weak to water. Not only can he not swim, he also moves at an extremely slow pace when under. In Sonic X he can't even move while underwater, and he can't move while on ice. There was an episode of Sonic Underground and Sonic X devoted to Sonic's aquaphobia. Also, in Mario and Sonic at the Olympic Games Sonic wears a life vest whenever he participates in a swimming event, in Sonic the Comic he has originally like the other Sonics cannot swim and he also moves at an extremely slow pace when underwater but unlike the other Sonics he learns to swim removing one of his weaknesses. Sonic Colors lessens this somewhat by giving Sonic an infinite jump underwater, and his Drill Wisp power works just as well underwater as it does underground.
In general, Revive Kills Zombie, so even undead bosses can be easily killed as long as you have a Phoenix Down in your inventory.
In Final Fantasy V, the Bonus Boss Omega, like hard bosses in general, are designed to have immunity to every status attack the player can throw at him... except for Romeo's Ballad. For some reason, this machine of death will specifically never be able to dodge a song about love, and will unerringly be frozen for a (very short) time because of it.
In Final Fantasy VI the irritatingly durable Platinum Dragons (formerly Wirey Dragons in the SNES version) have no elemental weaknesses and high offense and defense. However, Relm's generally useless Sketch ability triggers a monster spell called Cyclonic when she sketches a Platinum Dragon, and it knocks out 90% of their hitpoints. The Ultima/Atma Weapon on the floating island is extremely powerful and has a lot of HP, but dies when it runs out of MP, which it doesn't have nearly as much of. The spell Osmose absorbs a neat chunk of an enemy's MP and adds it to yours, while the spell Rasp destroys a large amount. Rasp, rasp, rasp, dead.
In Final Fantasy X, using Provoke on Defender X will force him to use an attack that halves the target's current HP for the remainder of the fight (unless the Provoker switches out of battle). Therefore, the fight becomes a Foregone Victory. Many other bosses have some exploitable weakness (some more obscure than others), making a "level one" run easier than you might expect.
The final boss of Final Fantasy Tactics, St. Ajora, is incredibly weak to the Oracle spells of Drain and Osmose, the two easiest spells to acquire for the class. The AI even actively hones in on characters using it by outright killing them if able, or depleting all their magic if not. However, even a single Chemist is enough to counter these effects, and you can merely have the rest of the party wail on the final boss without it even bothering them for an easy victory.
Vercingetorix in Final Fantasy XIII is brutally hard...unless you know he's vulnerable to poison. In that case, killing him is simply a matter of inflicting poison, then turtling in a three Sentinel paradigm until he removes the debuff, then repeating. It doesn't even take that long.
All of the final bosses of the MOTHER series are established as ridiculously powerful, perhaps even immortal, up until the final fight. Hitting it with any attack will do nothing, so you have to resort to attacking them emotionally. Giegue/Giygas from Mother is forced to retreat because Ninten sings the song his mother once sang to him, destroying his resolve. When Giygas makes his return in EarthBound, Ness and his friends have to send a call out to all of the friends and companions they made during their adventure, including you, who all begin praying that they will be safe, allowing them to win. And finally, at the end of the fight against Claus/Masked Man from Mother 3, Claus deliberately kills himself due to brotherly love.
In EarthBound, using the Jar of Fly Honey on Master Belch will make him stop fighting and focus on just eating it where you'll be given the whole time to drop his HP to 0. He's actually unbeatable if you don't do this to him, though, as his HP simply won't go down until then.
The Pork Trooper in MOTHER 3 is a rabid DCMC fan, and will waste multiple turns staring at you jealously if you show him a piece of their merchandise. The amount of attack power he possesses is high enough to make him a threat even with his attacks coming only every third turn, however.
The Ultimate Chimera, despite its name, is the only one that has an on/off switch on its back. However, it turns out that the silly-looking bird on its head isn't just a decoration and acts as a fail-safe of sorts, reactivating the chimera once the coast is clear...
In Baldur's Gate II, the extremely powerful liches rely entirely on magic in combat. There is a relatively low-level spell that allows you to polymorph into a 100% magic-immune and thus undamageable-by-liches creature: The Terrifying Mustard Jelly. Game Breaker ensues.
This is arguably also a case of Good Bad Bug, since mustard jellies aren't 100% immune to all magic under the AD&D rules that Baldur's Gate is based upon; they merely resist certain elements and status effects but are affected normally by other spells.
Taken even further with Bonus Boss Kangaxx. While he is definitely one of, if not the strongest enemy in the game, his death resistance is piss poor. There are so many ways of taking advantage of these, along with Good Bad Bugs, that someone wrote the song parody "Fifty Ways To Kill Your Kangaxx." ("Use Protect Against Undead, Fred.")
Cole from inFAMOUS has the standard "electric super" Weaksauce Weakness of water... but also has one in chain-link fences. The metallic mesh absorbs his shots and dissipates them harmlessly. He has to go around to shoot whatever is on the other side — since every last chain link fence in the game is capped with razor wire and can't be climbed. Penny Arcade didn't let this go without comment. It's even Lampshaded in the sequel — you can now climb over chain link fences, and there's a trophy for doing so for the first time, celebrating this amazing achievement.
He has another weakness: areas without flowing electricity. If there isn't an active power grid where he is, he suffers from severely blurred vision and is said in dialog to be generally impaired, though this doesn't really show in gameplay.
In Prototype, Alex Mercer and the Infected have a Weaksauce Weakness in water. Their biomass is too dense to float. Alex and Hunters will just jump back out of any body of water they fall into after a brief pause. The Infected not so much. However, it takes place on Manhattan Island, so besides the surrounding water that makes it an island, there's not a lot of water to use. Makes the quarantine easier to keep, though.
The "Bloom" technique, that causes flowers to sprout from trees, will also open bud-based enemies and reveal their weak point.
Umbrella-wielding and flying enemies are weak to "Galestorm" which most of the time isn't any more powerful than a moderate breeze.
The Tengu can be calmed down from going berzerk by causing it to rain.
The Big Bad is weak to sunlight, but then again, he is a god of Darkness.
The Bonus Bosses of Mana Khemia: Alchemists of Al-Revis are very powerful, to say the least. However, they all share a common monster trait that renders them vulnerable to a certain character's normal physical attack. Said character is one of the highest physical attackers of the game (plus, he also has a skill that increases his attack power even more), and abusing the weakness will quickly increase the Limit Break meter, allowing faster access to the uber-powerful Finishing Bursts. This is a saving grace, however, since one Boss Battle has you fighting three Bonus Bosses at once.
In Devil Survivor, the Nigh-Indestructible enemy Beldr is only harmed by Devil's Fuge AKA Mistletoe, which the only thing made of said plant you can get your hands on is a cellphone strap that is only made in the image of mistletoe. Makes up for it by being That One Boss of the game, but still a rather undignified weakness—but justified, due to the boss's background origin.
An odd case in Tales of Phantasia, which isn't a conventional weakness, but more of a developer’s oversight. The Bonus Boss of the Bonus Dungeon, Pluto, only has physical attacks, and one ridiculously long charging special attack, all of which have insane amounts of damage behind them, but must be used at close range. The first skill the main character ever learns is a long range, one SP cost move called Demon Fang', which instantly pushes Pluto back and flinches him. Hence, a Bonus Boss battle where the heroes stay on oneside and nuke the poor guy and the lead constantly pelts him with Demon Fangs, while the boss sits on the other side of the screen defenseless.
Castlevania II Simons Quest features the easiest fight against Dracula in the entire series. There are two weapons the golden knife and the sacred flame which cause Dracula to completely freeze in place. All Simon has to do is repeatedly spam those weapons, and he'll win before Dracula can even move.
In Castlevania: Portrait of Ruin, there's an optional battle with the spirit of Richter Belmont, one of the most powerful vampire hunters ever to walk the Earth. The easiest way to beat him is to keep throwing pies in his face, as the downward arc of the Cream Pie sub-weapon lets you safely jump and toss them while staying out of range of his whip and axe. Also the pies are Darkness elemental and boss is weak to Darkness, but that actually doesn't make much difference since the pies still aren't very damaging.
It seems that human(ish) enemies in the Resident Evil series are more vulnerable to melee attacks than they are to heavy firepower and ordnance. Krauser from part 4 is weak against Leon's knife, and in part 5, the first two fights with Wesker can be considerably shortened by clobbering him with as many QTE combos as possible.
In Resident Evil 4, the Plagas that hatch out of the various Ganados are either Demonic Spiders or Goddamned Bats, depending on your opinion. However, once "popped", they can be killed instantly with a single flash grenade... yes, that's right, the otherwise useless blue grenade you've probably been selling off for upgrades and beefier guns.
The final part of your fight with Krauser is a pretty tough boss fight...until you realize that your knife does about as much damage as a Magnum bullet and similarly causes him to stagger.
In Diablo II, a Paladin using the skill Blessed Hammer (commonly known as Hammerdins) are capable of throwing dozens of high-damage hammers at a time, even into the highest difficulties. Their weakness? Walls. Since the hammers arc in a circular pattern, it can be extremely difficult to defeat certain monsters who are positioned in a difficult spot. There's a reason why the most effective equipment for a Hammerdin has an item that provides the Teleport spell: because there's quite a few mandatory sections of the game that are best served teleporting around, avoiding enemies, grabbing the one item you need, and getting out of there.
Penny Arcade Adventures features a literal example: the special-attack weapon "Double-Mild Weaksauce" is such a wimpy hotsauce that it actually makes enemies wimpier and more vulnerable when you shoot it at them.
Although not a flaw of the units themselves, ground units in X-COM Apocalypse can only travel on roads and if the road square they are on is destroyed so are they. Especially galling with the Assault Tank which is pictured as having huge caterpillar treads but still can't go off-road.
In Nelly Cootalot, there's El Mono, who guards the gates to the mine/spoonbeaks' prison, with some pretty powerful (as Adventure Game standards go) magic. So what is an ordinary Pirate Girl to do? After doing a few more errands, the answer will come in the form...of an orange.
Kirby: Meta-Knight isn't afraid to get bloody in battle...but he is afraid of losing his mask. Every battle with him ends with his mask coming off, revealing that he's every bit as cute as the rest of the inhabitants of Pop Star. He immediately wraps himself in his cape and leaves.
Scarabs are somewhat easily beaten in Halo wars, stick an infantry unit too close for it to hit and send your army after it while it's stuck. They tend to die quick unless they have engineers.
While we're on the subject of Halo, in the first game, the Hunters were enemies who could easily ruin your day. The best way to kill them, other than a rocket, was a single Pistol round to the unarmored area in their back. That's right, just one Pistol bullet. Justified in-universe in that said pistol fired high-explosive armor piercing rounds, but still. Bungie nerfed this ability of the pistol in the games later in the series.
Kanbari in Shin Megami Tensei: Strange Journey is weak to physical attacks, and each hit against him generally results in a cooperative attack with your allies. To be fair, he's the god of the toilet, so players are right not to expect much. Be careful, however - Kanbari does know Tetrakarn (which reflects physical attacks).
The most likely candidate for the Big Bad of BlazBlue, Terumi, is, story-wise, one of the most powerful beings alive...and he is allergic to cats. Horribly allergic. So allergic that his joke ending has him reduced to a sniffling sneezing chew toy of the Kaka kittens. It's hinted to be canon too; in one scene he mentions that he hates the smell of cat. It's possible that Relius Clover, a Jerkass in his own right, added those allergies when he created Terumi's current body as a twisted joke.
Kratos from Tales of Symphonia's weakness is tomatoes. His son Lloyd seems to have inherited that weakness
Every playable character in the game has a least favorite food in the same way - Kratos' is just the only one that became memetic, probably because he's so stoic as to become The Comically Serious. It's not like they can ever get used against him in battle or anything.
Captain Novolin is weak against junk food. It makes him sick when he gets near it.
Hooktail, the boss of Chapter 1 in Paper Mario: The Thousand-Year Door, has a weakness to things that start with "cr" and end with "icket". This is because she ate some crickets a long time ago prior to the game's events, and the sound of crickets became so unbearable to her that she never wanted to eat a single cricket again. Equipping a certain badge that makes a cricket sound lowers her attack power and her defense drastically, making her easier to defeat.
Hooktail: Bleck! That awful sound! It... sounds like a cricket! How did you know?
In SimCity 4, most buildings and infrastructure will crumble to pieces if you move the ground near them.
Touhou: In Immaterial and Missing Power, Patchouli tells Youmu that she ought to be weak to fire since she's (half) an undead. Youmu replies that it doesn't apply to ghosts. In the end her human half turns out to be weak fire, but then again who isn't?.
In her scenario, Patchouli ends every fight by listing her opponents' weaknesses that often turn out to be weaksauce (although the validity or application are doubtful):
Sakuya: Asian ginseng, bitter melons.
Alice: Chili peppers.
Youmu: Bitter melons.
Remilia: Lots of weaknesses....
Yukari: Dried plums.
Suika: Fried beans.
Youkai are said to be able to regenerate physical damage very fast, but are weak to faith.
In Embodiment of Scarlet Devil, there's Rumia, the Stage 1 boss. She has the power to control darkness itself...but whenever she manifests this power, it blinds her and she starts walking into things. In other words, her weaksauce weakness is herself.
Finally Oni (which in this verse includes devils and vampires) are believed to be vulnerable to boiled beans, but apparently this is only because humans think so.
In the SNES The Wizard of Oz game, the Tin Woodman is normally useless, since he can't crouch or jump, but his attack is apparently the only one that can hit the Wicked Witch.
In The Legend of Zelda: A Link to the Past, Mothula is generally considered by far the most difficult fight in the game, since it's meant to be killed with the fire wand but most players don't have enough fuel to get the job done. However, you can deal massive damage if you unleash a bee on him... (It's worth noting that this is the only boss fight this tactic will work for, so perhaps the game designers realised how disproportionately difficult it was normally).
Minecraft's final boss, the enderdragon, is extremely difficult to defeat with a sword, and arrows take a long time to bring it down. However, they can be damaged with snowballs, which usually just knock mobs back without hurting them. Since snowballs can be stockpiled easily in a snow biome, and can be thrown much faster than arrows can be shot, they're probably the easiest way of winning the fight, and most people would never think to use them since they're harmless when used against 95% of the other mobs.
Endermen are damaged by water. Poor Endermen, caught out in the rain...
World of Warcraft is rife with such weaknesses to make otherwise impossible encounters winnable or just for amusement value. One great example is a quest where you have to get an artifact to defeat a pack of imps. The effect of this awesome weapon? It creates beautiful rainbows... cue sound of heads exploding.
The Aperture Science security androids in Portal will riddle you with bullets from their bottomless magazines ... unless someone tips them over. Then they plaintively self-destruct.
For some reason, vampires in the world of BloodRayne are vulnerable to water. Not just holy water or running water, any water at all will burn them. As half-vampires, Rayne is half as vulnerable, but it can still kill her if she's fully immersed, or if she stands around in a puddle long enough.
While the myth of vampires being weak to garlic is known in The Elder Scrolls, it isn't an accurate myth... with one, as far as the vampire in question knows, unique exception: Vicente Valtieri, who suffers a catastrophic reaction to being in close proximity with garlic. It doesn't kill him, but it makes him very easy to kill. Admittedly close here is so specific that it's not enough for you to carry it, he must do so — but you only encounter him in the Dark Brotherhood questline, which encourages sneakiness (and the game allows 'reverse pickpocketing' of placing objects in other people's inventories)...
In Dark Souls, for all its legendary difficulty, you would be absolutely amazed at how many bosses can be killed with Dung Pies. Seriously, you can literally kill some of the strongest bosses by flinging poop at them.
Cheshire Crossing (by the creators of Casey and Andy) delves into the weakness from the The Wizard of Oz: The Wicked Witch of the West explains that all witches are vulnerable to water (while in Oz, at least)—she was keeping the water on hand should Glinda the Good Witch launch a surprise attack. (In a later scene, the bucket is labeled "In case of Glinda".) She just never expected her enemy to bully a little girl into doing the deed.
It's more of a tribute than a spoof, but in Namesake, the Wicked Warlock of the West has the exact same weakness as his predecessor.
Toothgnip the goat in Goats gets his Kavorka Man powers from "The Panties of Potency". This had nothing to do with the artist having trouble drawing Toothgnip standing on all fours, honest!
Parodied in this strip of The Order of the Stick, where, since Haley always has her sandwiches without pickles, Crystal thinks they're toxic to her. They're not.
In one Bob the Angry Flower strip, Bob thinks that a superhero has the Weaksauce Weakness of bacon. He turns out to be wrong, but we never find out what the weakness actually is.
Another one has Bob running a hot peanuts stand, recognizing a customer and his friends as a band of supervillains, and instantly and correctly deducing that they are actually buying ammunition for an attack on Anaphylactic Man's fortress. (He sells it to them anyway.)
Yet another has Bob defeating an evil skeleton with the obscure knowledge that skeletons have a fatal weakness to raisins. Yeah, it's that kind of comic.
Tales of the Questor subverts this with the fey. General belief is that they are vulnerable to "Cold iron" but this proves to be false. Research into why the iron did not work reveals that the ancient documents that the information was obtained from were actually misprinted versions found in an ancient garbage dump and that the symbol for cold and the symbol for north are very similar. Turns out the weakness is not cold iron but "north seeking iron" (lodestone), they are vulnerable to strong magnetic fields. Unfortunately only the weakest fey have this vulnerability, the strong ones can shrug it off (though with immense pain).
Bob and George: Tomahawk Man is lethally allergic to Plant Shield, something Mega Man considers to be the crummiest power in the series. However, what really takes the cake is Ran Mark II, a monstrosity so intimidating it makes Bob virtually shit his pants. However, he is vulnerable to one of the most common substances in the Bob and George setting: Ran Mk I corpses. Bob, a demigod of fire, is flat fucking terrified of Pokémon.
In Goblins: Life Through Their Eyes, Klik, a sentient metallic being able to fly, morph into anything, and absorb genetic information from flesh-based life-forms, is corroded when coming into contact with blood.
In Sequential Art, the Denizens (little black shadow creatures) are dependent on their leader when they try to conquer the Earth. When he is killed, they just mill around the house, helping out or watching soap operas. And this leader can brandish a chainsaw, but just like the rest of them was small enough to be placed in a drinking glass and thrown out a window. Also, apparently Kat's evil former teacher's life is somehow linked to the ruler she waves at her students while yelling at them. When Kat breaks it in a fit of anger, the teacher has a heart attack and dies. And There Was Much Rejoicing.
This trope and the classic superhero Twinkie advertisements are brilliantly parodied in thisSuper Stupor comic.
The Evil, a litter of kittens made invincible, bloodthirsty fiends by Satan still suffer the psychological limitations of being kittens: give them milk, balls of string, or some toy mice, and they'll be too distracted and contented to murder you.
The demons of the Dimension of Pain can't stand the smell of flowers. This means that they can't enter the sewers in the Dimension of Lame, that place being a realSugar Bowl.
Charby the Vampirate: "Classic" vampires have all the classic weaknesses of the vampires, while "elites" possess none of the weaknesses, save one... Obsessive Compulsive Disorder. If they come across a pile of identical objects (a pile of rice, beans, the beads from a woman's dress that had accidentally come apart), they have to count it, regardless of the circumstances. For classic vampires, this can cause them to count until the sun comes up, and they die. For elites, trying to use this on them just ends up pissing them off, since the sun has no effect on them.
And Elites can still go around that with mathematics: Charby is seen weighting both a small sample and the whole heap on pocket scales, and deducing the total number from the sample size.
Liz's beast-man of a boss in Dead Winter doesn't really know how to fight, yet is still able to take on Monday pretty effectively due to his sheer giganticness and indestructibility. Monday stabs him in the shoulder, kicks him in a certain area, etc. but never really fazes him; the heroes end up smashing him in the head with a metal pole attached to a fast-moving car, but this only stuns him temporarily. His weakness? Germs—the imaginary kind. He's such a hypochondriac that slapping him in the face with a dirty mop will give him a panic attack. He gets over his fear of zombie infection pretty quickly, though...
Sydney in Grrl Power has seven orbs that grant her powers. But she has to hold an orb in her hand to use it, so she can only run two powers at a time. When asked what her weakness is, she said:
Sydney: So yeah. Mittens are my kryptonite.
The robots in Gunnerkrigg Court have the strength and speed of a machine, and some are safe even against Kat's electro-disruptor. But they have a big red button on top of their heads. Yep, they have a large, highly visible, easy-to-reach off switch.
In Nodwick, the Evil Sorcerer Ildomir went to a school for wizards called the Heractium Dark Arts Academy, where teachers punished students with a song called "I Write the Spells" (a Song Parody of the pop classic I Write the Songs) which also made them more evil. Unfortunately, this punishment was too much for Ildomir, and ever since, simply hearing the song would drive him to the brink of madness.
In El Goonish Shive, the fire-summon mooks have a weakness to water, despite not actually being on fire. Trying to make flaming creatures with a summon spell that can't allow it (the creatures would incinerate themselves) causes the effect.
Monkey and Secret Army 2 ends with the monkey becoming a superhero to battle the Giant Enemy Crab. He's going to beat the crab when it distracts him with bananas. He flies off and is not seen again until chapter 5.
In the Whateley Universe, The Fair Folk (and mutants who are turning into Fae) are vulnerable to cold iron. Wrought iron benches, cast iron skillets, and so on. But Fey is also vulnerable to synthetic fabrics which give her a burning rash. She could be incapacitated by rayon lingerie! (Or The Seventies.)
Phase subverts this trope by getting a fake weakness put on his powers testing results. Dark chocolate, administered orally. So now she can have enemies try to stop her by bringing her delicious desserts.
In the Global Guardians PBEM Universe, plastic, a substance unknown to the Ancient Greeks, is completely opaque to the Mask Of Justice's vision powers. Thus, he can't even see through Saran Wrap (tm) while wearing his mask. (This weakness extends to other substances unknown to the Ancient Greek magicians, but plastic is the one that keeps coming up.)
Mongibello, a "geokinetic" who can control and move earth and stone, can be rendered powerless simply by picking him up, or otherwise prevent him from touching the ground.
Eddsworld: In one of the early Christmas specials Edd is saved form death when he finds the Grim Reaper's one weakness: Gravy.
The Centaurians in The Pentagon War are cold-blooded. They automatically hibernate whenever it gets too chilly.
In Group Of Weirdos, the Iron Knuckles are completely invincible, unless tag-teamed and attacked repeatedly by Link, the hero of time, and Ganondorf, a dark wizard with great power. Or you can just slash them a few times with a Deku Stick.
Maybe going to the toilet is like his kryptonite. "I'm going to kill you! Heh heh heh... what's that, you need to go Number 1? Here, I'll just wait outside while you deal with that, OK? Make sure you wash your hands, OK, I don't want it to be gross when I kill you. Well, I do, but not like that."
The titular character of Invader Zim is a member of a hyper-advanced, genetically engineered race of aliens for whom Humongous Mechas are a mundane occurrence and whose sole purpose seems to be conquering the entire universe. His main weakness? Water (possibly just polluted water) and meat.
Captain Planet, being a paragon of clean Earth, is weak against your usual forms of pollution (smog, toxic waste, etc.), as well as Hitler-level hatred, apparently. You might consider these not particularly weaksauce, but it suggests Gaia went seriously wrong in the design stage: the things he was created to fight against are the things that do him the most damage. It's like J'onn J'onnz deciding to be a firefighter or Alan Scott deciding to only fight evil loggers.
His evil counterpart Captain Pollution has an even lamer weakness: direct sunlight, lack of pollution, and clean water. Yes, any remotely clean source of drinking water sprayed in his face will make him bow down and crawl helplessly. This seriously deters his ability to establish himself as a credible threat.
Namor the Sub-Mariner of Marvel Comics is similarly affected by pollution (though not by hate, which is good, since he seems to run on it), but that makes sense, as he's a water-breather. Because he's a Half-Human Hybrid, he's also subject to insanity and fits of rage if he stays submerged for more than two weeks. Or emerged for more than two weeks. So he needed to switch environment every week to stay sane. Until authors simply forgot the issue.
His brother Carl, The Evil Cockroach Wizard has been shown to be a very powerful villain capable of global domination himself, he has one glaring weakness: self-esteem. He's been defeated by insults and peer pressure, and his own low opinion of himself keeps him from going full-tilt against the heroes and his brother.
Birdman from the old Hanna-Barbera cartoons had the powers of flight, energy beams that shot from his hands, enhanced strength, and a personal force field — and drew his powers from the light of the sun. Fair enough, there are plenty of other solar-powered heroes out there (Superman, Cyclops (sometimes), Starfire). Unlike those heroes, however, Birdman apparently had no energy reserve; he became weak as a baby after being removed from sunlight for less than a minute. As it was implied that being out of the sun for an extended period of time ("extended" apparently being something like five minutes) was fatal to Birdman, it's a wonder he didn't spontaneously drop dead at night. No wonder he became a lawyer. After he became a lawyer, he developed a new Weaksauce Weakness; he's completely worthless if he loses the Birdman insignia that he keeps on his forehead.
In an episode of Ben 10, it turns out that the leader of the Galactic Enforcers (an alien superhero team, said leader an obvious parody of Superman) has a devastating weakness to chocolate, which Ben himself points out is a lame superweakness.
The members of the Sushi Pack are rendered powerless by any kind of heat, but even worse, they feel compelled to announce this every time a villain pulls out a heat lamp.
WordGirl isn't so much defeated by a cute little kitten, but rather easily distracted by one. She also compensates for her language abilities by showing a complete lack of competence in art, poetry, and dance.
Parodied in Futurama: "The human was impervious to our most powerful magnetic fields, yet in the end he succumbed to a harmless sharpened stick!"
An episode of Martin Mystery had an alien fungus monster that had taken over a small town and replaced the inhabitants with clones. Both it and the clones could be killed with salt. As luck would have it, the small town just happened to be in northern Utah.
Mumm-Ra from ThunderCats, with a weakness to his own reflection. The writers eventually realized this made Mumm-Ra too lame, so they had him get over it. The Thundercats had a harder time dealing with him after that. Even more so when he got an Infinity+1 Sword of his own.
Plutar was weakened by soap. The show was so far in the future that modern society was all but forgotten; soap was treated as an ancient science.
When Buttercup wanted to become a better superhero in "Super Zeroes", she became Mange, a knockoff of Darker and Edgier comic book Anti Heroes — Spawn in particular. However, when the time came for her and her sisters (both of whom also assumed their own "better superhero" identities) to go out and fight a monster destroying Townsville, Mange was the only one who stayed behind, saying it's too bright and that she only travels at night. Mange then spent the rest of the day sitting on the couch with Professor Utonium until night fell, arriving too late at the scene as the monster had already left (her sisters were also late for reasons of their own). The three girls spent the night under a tree. When the monster came back to face the girls again, Mange sits out the fight, preferring to stay under the tree's shade. This attitude led the monster to eventually call her "Little Miss Darkness who’s afraid of a little sun".
Being kindergarteners, the girls have plenty of weaknesses of their own any other time—they have been shown to be deathly afraid of "cooties", cockroaches, and broccoli. The episodes these weaknesses show up in usually involve some sort of super-powered or evil version of it, so it's not always so silly...
There's Antidote X which was used in only one television episode ("Slumbering With The Enemy", on the girls themselves) and in the movie (on Mojo Jojo).
Mojo also tried to use it in another episode where he also used Chemical X to give his then-partner Princess super-powers. Unfortunately, this backfired on both villains, and Princess was hit with the Antidote X, letting the Girl trounce them both.
The original incarnation of their Spear Counterpart enemies the RowdyRuff Boys are so grossed out by the girls' kisses that they explode. And after being genetically modified to actually gain strength from this past weakness ( aka puberty), they gain a new weakness, humiliation. Yes, humiliation. Anytime they are embarrassed and laughed at, they shrink.
The titular creatures turn into immobile statues during the day, which leaves them extremely vulnerable. They try to work around this in various ways (working a deal with humans in exchange for protection, magic spells, etc.) However, this is actually a bit of a double-edged sword. Though vulnerable as stone statues, they are COMPLETELY healed of almost ANY wounds (even potentially fatal ones) when they return to flesh and blood. Hudson, being the most experienced of the main cast, uses this to his advantage, defeating the better armed and fitter Demona while protecting an injured Goliath by simply keeping her at bay until dawn. When the sun sets, Goliath is healed and they easily dispatch her together.
Oberon's Children, like other portrayals of The Fair Folk, are all vulnerable to iron. Iron can disrupt their magic, actually hurt them, and imprison them. In his not really first appearance, Puck is forced to obey Demona after being bound with iron chains. The Weird Sisters are also coerced into doing a favor in exchange for being released from an iron chain. Later, The Trickster Coyote is trapped in the robot Coyote's latest body which was constructed with iron from a magical cauldron. Their ruler Oberon, while not immune to iron, is powerful enough to withstand being impaled by an iron harpoon though it does cause him to wither in appearance for a short time. (An Iron bell on the other hand, can easily kill him.)
One episode of My Life as a Teenage Robot has an incredibly powerful, sadistic, and sexist supervillain, Himcules, who gets stronger and stronger anytime he causes someone pain, and of course, he appears right after Jenny has implanted sensors in herself that either tickles herself or causes her pain. Stuck in "Pain" mode, Himcules continues to gain more and more muscle (and even pleasure) every second he makes her cry in pain... then she comes upon a little girl who kindly (sorta) switches her "Pain" switch to "Tickle", and it just so happens that laughing at Himcules is his only weakness.
In Teenage Mutant Ninja Turtles: Fast Forward Sh'Okanabo's first attempt to infect Earth with his progeny is thwarted by...sunlight. Although this is handwaved as a particular, unexpected feature of Earth's, and Sh'Okanabo himself is not normally affected, dealing with his weakness is the thrust of his character arc throughout the remainder of the season.
In one episode of The BOTS Master, the Big Bad uses a special alloy to make his Mecha-MooksNigh Invulnerable. The good guys think that they're screwed, until the inventor of the alloy tells them that the alloy can be dissolved by...citrus acid. In the end they use lemon juice to defeat the new Mecha-Mooks.
Felix Renton's Super Wheelchair is one of the most advanced pieces of technology in the series. It can hover and has Combat Tentacles. But it can be hijacked by a wireless game controller.
One of Dr. Drakken's schemes was to create an army of Kim Possible clones. The scheme failed when Wade figured out that the clones were chemically unstable and would melt if exposed to carbonated soda.
Not exactly canon, but when he retells his origins in "The Secret Origin of Darkwing Duck," he describes meeting another hero whose weakness is Coo-koo Cola. She winds up falling into a vat of the stuff at a factory and, well ... adds to the Disney series' death count.
There's also Comet Guy (Super Weight: 4), whose Achilles' Heel is that every time he hears the sound of a bell, he starts dancing mindlessly until he hears a whistle. His intellect might also count, but frankly it probably can't even do 2+2.
The Fairly OddParents: All that fairy magic is neutralized when they are under a butterfly net. There's also all the various "Da Rules" which prevent them from undoing some of the more disastrous wishes, but do nothing to stop them from getting into these situations to begin with. One thinks an "I wish that no wishes that will somehow prevent me from undoing those wishes can be cast" wish might save a lot of trouble.
Desiree's main weakness is that she has to grant every wish she hears, including wishes like "I wish you were defeated."
The Fright Knight is also stupidly vulnerable. If his sword gets sheathed in a pumpkin, he is instantly defeated. His worst nightmare is probably somebody using an ordinary pumpkin as a shield.
Mighty Ray of Hero 108 has the ability to shoot lightning from his eyes. The drawback is that he has to eat a banana to do it...and he hates bananas. He can also have his eyes knocked out of his head, which happens more often than you'd like to think.
Several characters from CatDog refer to this trope as "Porkfat", named after the weaksauce weakness of the in-universe movie character, Mean Bob.
Bureau of Alien Detectors: When making an unstoppable zombie army, it's a good idea to ensure that the one thing that will kill them doesn't exist naturally in the atmosphere. Oxygen.
According to God, the Devil and Bob, Satan can't stand Tony Orlando songs. This comes in handy the one time he actually tries to knock off the comedy routine and physically attack Bob.
Ben 10: Ultimate Alien features in one episode an otherwise-invulnerable plant monster that dissolves on contact with... peanuts. No explanation is given beyond "it's allergic".
The Imperium, White Martian expys in Justice League have an even greater weakness than the usual fire. Direct sunlight causes them to burn and evaporate near instantly. One would think they'd be moving along planet systems away from suns, but no.
The controversial Looney Tunes short "Wagon Heels" features Injun Joe, The Superchief as its villain. Injun Joe is a powerhouse: he shatters mountains and laughs at gunfire. But Porky Pig's sidekick Sloppy Moe knows Injun Joe's secret weakness. He's ticklish!
In Batman Beyond, the assassin Inque is vulnerable to: water, electricity, severe cold, and dehydration. Despite this, she's likely the strongest villain in the series (in terms of physical power), who has likely come closer to killing Terry than anyone else (even his Arch-Enemy Blight), and while he has defeated her, he has always needed help from someone else to do so.
In The Transformers, the Decepticons were once driven off by a fire suppression system that sprayed them with fire-retardant foam after Megatron claimed it would short out their circuits. Why this doesn't make Inferno and Hot Spot (Autobots who turn into fire trucks) into the Decepticons' primary nemeses has never been explored.
In what may be a weird mixture of Call Back and Running Gag, Sideways in Transformers Cybertron and Starscream and Blackarachnia in Transformers Animated have also been incapacitated by fire-retardant foam for varying lengths of time. This includes the foam from a traditional human-sized fire extinguisher, in the case of Sideways.
In the Talespin episode, "Pizza Pie in the Sky", the normally healthy and active Louie is severely allergic to anchovies. One whiff of the irregular anchovies that Baloo and Kit bring him is enough to make him ill and delusional.
Avatar: The Last Airbender: Element-bending is basically Supernatural Martial Arts combined with Elemental Punch, meaning that you can stop the craziest of superpowered benders by tying up their hands and legs. Though there are those with whom even that won't work (Aang can blow people away with a sneeze, Iroh can breathe fire, Bumi can earthbend with his face, Yakone and Noatak have demonstrated psychic bloodbending, Combustion Man and P'li can blow things up by thinking at them, and Ming-Hua can waterbend despite having no arms.
In the season 4 premiere of Jackie Chan Adventures, Tohru threw an onion at Tarakudo on the strength of his mother's fairy tales about onions repelling oni. Tarakudo screamed about his eyes burning and vanished. Several episodes in we get Jade digging an onion out of a dumpster.
Tarakudo: No! Anything but onions! (Jade throws it at him.) My eyes! My eyes! (poof)
Life as we know it is remarkably fragile; too little or too much of any one thing can kill. In fact, except for (parts of) the surface of one small planet, there is no known place in the universe where an unprotected human could survive more than a few minutes.
Allergies. Nuts, animals, shellfish, bananas...in the case of peanut allergies, some cases are so severe that people could be in serious danger just by being in the same room as peanuts.
Some people suffer from Aquagenic Urticaria (water allergy). That's right, there's people who were unfortunate enough to be born allergic to a substance they can't live without. Any moisture build up on their skin aggravates the condition, so they must carry umbrellas with them at all times, avoid heavy clothing/exercise to prevent sweating and prefer to remain indoors in well ventilated surroundings. For all their precautions, though, they still have to wash themselves with water regularly.
There's a lot of stuff that can incapacitate a human. Tickling is a lot of peoples' weaknesses and a lot of people have a sound that 'goes through them' like the sound of plastic folders being rubbed or nails on a blackboard.
British sailors in the 19th century hated eating fish or any food from the ocean for that matter, preferring weevily biscuits and gruesome salt pork or beef to fresh fish. Sailors hate the sea, pilots hate the wind, and retailers hate customers—Weaksauce Weakness in its truest form.
The skins of land snails and slugs are water permeable, and as such, are extremely vulnerable to fatally drying out. It's also why they're limited to dark, moist environments. Salt kills land snails and slugs by screwing up their osmotic balance, in that the salt speeds up the drying process by pulling the water inside of their cells and internal organs out.
Giraffes can easily suffer fatal neck and head injuries just from falling over. Don't believe it? Just imagine the whiplash with a neck that long... This is true of most large animals—the bigger you are, the worse falling over is for you. That's why, for example, elephants keep at least 3 legs on the ground when running (rearing up on their hind legs, as is sometimes seen in circuses, is not a natural behavior). Gravity is a bitch.
Most electronic devices can be damaged irreparably by brief contact with water.
It isn't the water that kills it. All electronics are only good up to a certain voltage or current. Go beyond the specification of a given part for either and it goes boom. Water simply provides a method of short circuiting the gadget, thus bringing the current over what the electronic likes, usually. If you dunked a cellphone (without the battery) in water and let it dry for a day or two, it could still operate. Wouldn't recommend you try it though.
In fact, the best way to clean your keyboard if it can take the abuse? Run it through the dishwasher.
When an electric device has become wet it can be dried quicker by first dunking it in another fluid (that may or may not be able to shortcircuit the electronics by conducting electricity itself) with a lower boiling point. This fluid will replace most of the water in the device and afterwards evaporate quicker, leaving the device dry and ready to use sooner.
Static electricity can do this as well if you touch electronic components directly while carrying a charge in your body. Your desktop can be murdered by your carpet.
Modern electronics are often powered by Lithium-Ion batteries because of their high charge speed, stable voltage and limited charge decay. Problem is that lithium catches fire in contact with water. A damaged battery must be discarded immediately. This is applicable for electric cars as well - battery fire has destroyed a fair deal of vehicles that way.
The transport infrastructures of many countries (such as the UK) are vulnerable to ice and snow. That includes roads, rails, and airports.
The UK rail network is (in)famously vulnerable to leaves.
Aircraft that employ stealth technologies can very easily lose their stealthiness to the most mundane of things.
The F-22 "Raptor" is one of the most advanced stealth fighters in the world. Yet the radar-absorbent coating can be easily damaged by water, significantly increasing its visibility to radar.
The F-117 Nighthawk, the world's first stealth fighter, had a radar-absorbent coating that would be ruined by just leaving fingerprints.
Irrational fears can be constituted as weaknesses. If you're lucky enough to catch one of those Maury episodes, you can see fears of mustard, butterflies, lettuce, and so on.
Some people with PTSD have triggers of the Nightmare Retardant variety that, out of context, seem laughable to those who aren't triggered by them, but remind them in some way of their traumatic experience and can trigger anything from an uncomfortable sensation to a full-blown flashback of the event. To make things worse, people with this kind of trigger will sometimes experience belittlement if they dare to disclose it.
Worse is the way Kryptonite Is Everywhere; people could understand if a loud bang causes someone who'd been in a war zone to flash back to a bomb strike, but what if a certain enemy vehicle sounded a lot like a certain civilian one, or someone was holding a cup of McDonald's coffee just before the worst attack they'd lived through? Suddenly a car in need of a tune-up or a cup of coffee on a table is Kryptonite to a Colonel Badass who eats nails for breakfast. One could also easily imagine a person who has suffered abuse needing to, say, not watch Law & Order: Special Victims Unit if they'd been molested. But some could watch it all day, and then the mailman comes by wearing the same brand and color of shoes their abuser preferred.
Going a night or two without sleep can severely weaken you, both physically and mentally.
Optical discs themselves (especially those which have two shiny sides) have a Weaksauce Weakness - simple tape. If one pastes tape or a label on the front of some discs, then decides to remove the tape or label, the adhesive peels off the data-containing foil layer, rendering the disc unusable. This is because the disc has almost nothing between the foil and the label side of the disc. The fact that the disc is shiny on the label side as well as the data side shows that the disc has no protective label printed onto it, only a thin layer of plastic that is easily removed. In fact, any optical disc is much more likely to be ruined from the label side than the data side because of the thinness of that side, even with a factory-printed label.
Doctors have a working understanding of the entire human body, and require the cognitive capacity to make fairly accurate life-or-death decisions with a scant amount of information. But ask them to print legibly...
Phobias in general can be like this for those who suffer from them; they cause crippling, irrational panic at the slightest indication of the feared objects. Worse, being irrational after all, the object doesn't even have to be objectively frightening. Most of us can probably understand why people would be afraid of spiders, or snakes, or heights, but imagine having a phobia of flowers, buttons, or peanut butter? (Imagine it too hard and you'll get phobophobia...)
Laser weapons that are starting to be used by the US military can be thwarted by such extremely rare phenomena as dust, sand, bad weather, clouds, smoke, steam, etc. As Stephen Colbert put it, it's a good think they're not planning on using it in regions that have above-mentioned problems, or if Iran develops sand technology.
People can pass out by locking their knees for too long. This isn't normally a problem, but people who have to stand still for long periods of time, such as people in the army, marching band, or choir, have to make sure to bend their knees occasionally.
Animals with strong clamping muscles, such as crocodiles or lobsters, tend to have weak muscles for opening. Their main weapon, whether it's a mouth or a claw, can be rendered useless by a rubber band.
Read the "Orion" entry above? Well, primeval (anaerobic) bacteria have the same problem (and early life on earth was in real trouble when oxygen accumulated).