Kryptonite Factor

"Hey Clark, check out this awesome glowing rock I found! Clark? You okay?"

"Likewise, in fiction, whatever power a character has must have a downside somewhere, or he becomes a boring Superman type of character who can handle anything and get out of any difficulty, and he won't interest readers for long."

— Timothy Zahn

The Kryptonite Factor is an Achilles' Heel where the weakness is something that affects the Superhero and typically just them, as it will have little to no effect on others. It typically comes as a rare material, specific mental hang-up or abstract limitation in their abilities, any of which can be a Power Nullifier. Fundamentally this is to show that no one is invulnerable, not even our godlike main character. This is especially ironic if the vulnerability is completely arbitrary and oddly commonplace.

The more powerful a character is, the more likely the Kryptonite Factor will be abused. Writers in particular tend to dislike immensely powerful characters with a single Kryptonite Factor, because not using it creates a drama-destroying sense that the character is never under a serious threat. Conversely, if Kryptonite was supposed to be rare it strains credibility when it starts showing up everywhere.

This comes as a contrast to Logical Weakness, wherein the Achilles' Heel comes about more naturally through understanding the real-world nature of their abilities (ie water-based powers are vulnerable to electricity-based powers) or being consistent with the fictional depiction of how their powers work.

The name comes from kryptonite, the bane of Superman regardless of how powerful he is being portrayed at the time. A literal green rock, it seemed unusually abundant in supervillainous hands for being radioactive bits of a planet that exploded lightyears away. Many Elseworlds and spin offs to the Superman mythos include characters who are more resistant to kryptonite, but conveniently, not as strong. Thanks to Superman being a Long Runner, and Pop-Cultural Osmosis, a common bit of Memetic Mutation is to refer to something you are particularly vulnerable to as "My Kryptonite".

Compare Supernatural Repellent, which is not specific to superheroes. See also Kryptonite Ring, Kryptonite-Proof Suit and Fight Off the Kryptonite. Contrast De-power, Cross-Melting Aura and Drama-Preserving Handicap. Related to Why Did It Have to Be Snakes?. If the character is vulnerable to something comparatively mundane (and even non-threatening), that makes it a Weaksauce Weakness. When this trope turns up far more often than seems probable, see Kryptonite Is Everywhere. When this extends to having characters whose powers are nothing more than a Kryptonite Factor, you have a Man of Kryptonite.

Super-Trope to the Verbal Weakness, which is this trope in auditory form.

Not to be confused with The Krypton Factor. By the Power of Grayskull! is more or less the opposite, giving powers as opposed to taking them away.

---

Examples:

Examples on subpages

• Comic Books
  • The DCU
    • Superman
  • Marvel Universe
• Fan Works

---

Anime & Manga

• Anpanman: The titular hero has a head made of bread, which is his weak point. If he breaks off too many pieces of it to feed others, or his head gets wet, dirty, bruised up, or moldy, he loses his power. Once a new head is put on, he gains all the energy he needs again.
• Assassination Classroom: Revealed very early on is a rubbery material that, to humans, is about as damaging as actual rubber, while messily popping Koro-Sensei's flesh even on quick contact, and being able to kill him off if it strikes near his heart. However, this doesn't help much; you still need to make contact with it, which is easier said than done when fighting someone with a Mach 20 Flash Step.
• In Bio-Meat: Nectar, B-M go dormant in direct sunlight. (Only direct sunlight, though, so if it's overcast you're in trouble.) They also tend not to react well to flames, enough that hairspray and a lighter makes an effective tool against singular B-M. There are high-tech experimental weapons that break them down at a genetic level, but they're rather rare, delicate and have a short battery life.
• Black Bullet: The monsters known as Gastrea are practically invulnerable to normal weapons, but weapons and bullets made of the metal Varanium can harm them, and monoliths made of Varanium can drive them away. However, there are Gastrea that are powerful enough to ignore the monoliths. Due to Fantastic Racism in the series, it's been also used against cursed children who are born with the virus. A group of cursed children that Rentaro taught were killed by a bomb filled with Varanium shards.
• Call of the Night: While it is unclear exactly how much sunlight weakens vampires, all of them have an inescapable weakness in the form of an object from their days as humans to which they have a strong emotional attachment (such as a present to/from a loved one, or something to remember them by). Physically touching said object, or even just being in very close proximity to it will stun the vampire and nullify their Healing Factor, leaving them vulnerable. In some cases, prolonged physical contact can even drive them into a frenzy. Being a dhampyr, Nazuna is initially assumed to have no such weakness since she was never human... until Kiku finds one in the form of her umbilical cord.
• A Certain Magical Index: Saints are people born with physically perfect bodies similar to the Son of God. This gives them great powers like incredible levels of Super-Strength, Super-Speed, Super-Toughness, etc. However, they are vulnerable to any of the tools that were used to torture Jesus. For example, if an ordinary person punched them or hit them with a baseball bat, they could easily shrug it off. But if a Saint was hit with a cross, crown of thorns, scourging whip, etc, the item would hurt them like it would a normal person. There are also spells designed to combat Saints, like the appropriately named "Saint Destroyer".
• Don't Meddle with My Daughter!:
  • Athena and her daughter, Clara, are a parody of Power Girl and Supergirl respectively and have the same basic set of powers. Their weakness...? It's sexual harassment. In their setting, virtually everyone is a pervert from the villains, to the bystanders they put themselves at risk to protect.
  • For Athena in particular, the constant shame and degradation she had to endure forced her to retire 20 years prior to the start of the series. But after learning her daughter had taken up her mantle, Athena dons her cape again to protect Clara, from the shadows.
• In Fairy Tail, Wendy has this in the form of sour foods, like dried plums. She was once defeated simply by watching someone eating dried plums. Meanwhile, Natsu suffers from debilitating motion sickness whenever he's on any kind of moving vehicle.
• In Fullmetal Alchemist (2003), the homunculi become vulnerable when they come into close proximity to the body of the human of whom they are a Shadow Archetype.
• Ingress: XM fields and Portals impair or outright cancel the abilities of opposite-aligned Sensitives (ej, Jack of the Resistance cannot use his future-sight power while inside an Enlightened field). In some cases it may even prove debilitating/mentally taxing to Sensitives, although this is never shown in the anime. Now consider that XM is everywhere and that anyone with the Ingress app can do something about the fields and Portals.
• Inuyasha:
  • Inuyasha temporarily loses all of his demon-powers on nights with a new moon.
  • There's also Miroku, who has a miniature black hole that is initially a game breaker. So the show introduces poisonous wasps which can kill him if he sucks them up. These practically become the villain's trademark so that only Inuyasha can be a credible threat to him.
• Knights of Sidonia: The alien Gauna can only be killed by a peculiar metal substance called "kabi". Even such things as planet-buster warheads will do nothing to a Gauna's core, and it will regenerate all damage, but so much as touch the core with kabi and the whole thing falls apart permanently. The Sidonia ran across a giant, seemingly artificial but abandoned structure made of the stuff and harvested what they could before a Gauna attack forced them to move on. They have to be very careful with the couple dozen spears they made out of it because they don't have a clue how to manufacture it nor where more can be found.
• Kotetsu Jeeg: The titular mecha is weakened when making contact with electricity as it affects the magnetic power that binds his body together. Episode 5 also reveals that strong magnetic storms like solar flares prevent him from combining (at least until they made a special coating spray).
• Maken-ki!: For most of the world, Yamato Takeru is a seemingly unstoppable force of evil. Made moreso, since he's already dead, has near godlike combat prowess, and has numerous clone bodies to inhabit. The only thing that can hurt him is "White Element", which is so rare, that there are only four known ability users in the world that can use it. The protagonist, Takeru Oyama, happens to be one of them.
• Marry Grave: The only way to actually hurt Sawyer is to attack Rosalie's body, any wound done to her corpse will appear on Sawyer too.
• One Piece:
  • Anyone who has eaten a Devil Fruit has two, related Kryptonite Factors: the ocean, which causes power leeching and an inability to move due to weakness, and Seastone, also known as Kairouseki or as "Sea Prism Stone", which replicates the effects of the ocean and out of which most prisons in the One Piece world are built.
  • The effect of Seastone and the sea itself varies from user to user: Luffy (a paramecia user) and Chopper (a zoan user) have severe and painful reactions to either but are still made of rubber (which is used to save his life when he's drowning in the ocean) and a human-zoan respectively, while logia fruit users and other paramecia users are simply unable to use their powers.
  • Smoker also has some Kairouseki on the end of his jutte, despite his being a fruit user himself (the weapon is long enough to keep him from coming into direct contact with the stone).
  • Often applies with individual Devil Fruits through Elemental Rock-Paper-Scissors, particularly Logia. As an example, the fact that Luffy is a Rubber Man allowed him to break the normal Sorting Algorithm of Evil by easily defeating Enel, whose electric power made him close to a Physical God.
  • The Yami Yami no Mi also appears to act as kryptonite to Devil Fruit users and seems to have been built just to combat them: of the two abilities shown so far, creating black holes (and expelling anything and anyone pulled in), and canceling Devil Fruit powers, only the first can be used on normal people.
  • Busoushoku Haki (Armament Haki) allows the person who use it to surround themselves with a thin but powerful armor (it's mostly invisible until the Time Skip), allowing the user to negate Devil Fruit powers by contact. It does not cancel the Devil Fruit power itself, but it's one of the few methods of attacking and hurting Logia-type users. Trained Haki users can use their Busoushoku Haki for their projectile weapons or Devil Fruit powers. And if the Logia-type user has their own Busoushoku Haki, the attacker's Busoushoku has to be stronger in order to bypass their intangibility. A sufficiently advanced Haki user can even resist a Devil Fruit user's powers, though they are still unable to cancel it entirely.

Films — Animated

• The title character of Bolt is a dog on a TV show who thinks his superpowers are real. When he is accidentally placed in a box and shipped to New York, he finds that he no longer has superpowers, and thinks the Styrofoam peanuts in the box are the cause of it.
• In Megamind, the eponymous villain accidentally defeats Metroman by trapping him in a room lined with copper, his previously unknown weakness. It turns out to be a trick to allow Metroman to fake his own death.

Films — Live-Action

• In Dracula Untold, vampires have the standard array of weaknesses: silver, sunlight, wooden stakes, and crosses. Also played with a bit. Crosses only work on permanent vampires, the ones that have fed on humans. Those like Vlad, who will turn back in three days, are unaffected. Stakes, on the other hand, are not only effective but ridiculously so; when Mehmet goes after Vlad with a stake, his armor actually evaporates around it so the stake will hit flesh.
• Godzilla, in the film Godzilla vs. Biollante is revealed to be weakened by the ANB (AKA The "Anti-Nuclear Bacteria"). Though, for some odd reason, it's never used again in later films.
  • That was because it simply didn't work because he was cold-blooded, and had to have his body temperature raised beyond normal; which the military did do, but it was a hassle, and Godzilla was able to recover by going into the ocean. (In all fairness, he passed out right on the shore.) Simply put, the ANB was too much work to pull off and needed an elaborate setup. Particularly given that while they knew how to make it, the guy with the expertise with genetics to do so is killed shot precisely for his capability with it, making utilizing it even more difficult.
  • A more reliable weakness specific the Heisei Godzilla has is cadmium. However, it only works if fired into his mouth and it requires a significant amount to do more than weaken him.
• In a dream sequence in Harold & Kumar Go to White Castle (aka H&K Get the Munchies), the bullying sheriff gets to say this terrific line after he gets shot: "Bullets! My only weakness! How did you know?"
• In Highlander all of the Immortal characters are just that; they are able to shrug off almost any wound, they're immune to all forms of disease, do not age a day in their life and are even capable of surviving without oxygen. The only proven method for defeating them is decapitation.
• In Lemonade Joe, Joe is a strong, tough guy with Improbable Aiming Skills. There is one substance that is his Achilles Heel and makes him lose consciousness, leaving him at his enemies' mercy. It's alcohol.
• Lampshaded in Sky High (2005) - instead of arbitrary medical checkups, students are exposed to Green Rocks of different colors to check for weaknesses.
• Lampshaded in Unbreakable. David is a horrible swimmer and nearly drowned once as a kid. Discovering this was evidence reinforcing that he was actually "unbreakable" because all heroes have some sort of weakness. Another character points it out to him, saying "that's your Kryptonite."
• All superheroes in Up, Up and Away! are weakened by tin foil. Too much is fatal. When the main character's friend brings over a meal that's wrapped in foil, the parents (all supers) treat it as a bomb and then bury it in the yard. The Big Bad finds out about this and then goes to the nearest grocery store.
• In Who Framed Roger Rabbit, Toons are invulnerable to conventional damage, but can be injured or killed by a specific blend of paint-and-ink-thinning chemicals, known as "the Dip". Immersion is fatal, and a Toon cab who'd skidded through a puddle of Dip suffered four flat tires and was left limping in pain. They also can't let the ol' "Shave And A Haircut - Two Bits" go unfinished. Roger ends up ruining their hiding spot because of it.

Literature

• In After the Golden Age, Captain Olympus is a Nigh-Invulnerable Flying Brick, but he has one weakness: the same radiation that originally gave him his powers.
• The Alteriens of Adam R. Brown's Alterien are pretty powerful, but they too have their weaknesses. Iron objects can hurt Alteriens, going so far as cancelling out their ability to absorb kinetic energy. As such, an Alterien can be cut or even killed with iron. However, it takes far more than a cut to kill an Alterien. It would take the same amount of effort as it would for a human using an ordinary knife or sword. This means an Alterien can die if beheaded or cut in half by an iron blade or stabbed multiple times with iron to the point of overtaxing their healing factor. Alteriens such as Oberon are also vulnerable to areas of concentrated dark psychic energy. Whenever Oberon is in or near such an area, he becomes very weak and his ability to absorb energy is reduced.
• In Attack of the Mutant, main character Skipper Matthews defeats the titular Masked Mutant by claiming to be a superhero whose only weakness is sulfuric acid. The Mutant, a shapeshifter who can turn into anything solid by rearranging his molecules, promptly turns into a wave of acid... which is a liquid, and so he can't turn back into his normal self anymore.
• Parodied by Captain Underpants, who thinks he loses his powers when he's sprayed with starch. It's actually a Placebo Effect, because he only believes it because that's what George and Harold wrote in their comic book.
• The Dresden Files: A wide range of mythological monsters exist In-Universe, and they typically have some version their mythological weaknesses. Some prominent examples:
  • Faeries have a crippling weakness to iron. It burns even the most powerful Fae on contact, and mortals bestowed with their power (the summer and winter knights) lose it on contact with iron. It's noted that the term "Cold Iron" is purely poetic: anything with enough iron (or steel) in it will work.
  • The Black Court of Vampires (there are 3 Courts featured in the novels and a few more mentioned) have the laundry list of standard vampire weaknesses including garlic, holy water and sunlight. In universe the weaknesses became public knowledge when the White Council helped with the publishing and spread of Dracula to help humans defend themselves. It was so effective the Black Court was hunted to near extinction.
  • The White Court of Vampires are burned on contact with the emotion opposite to what they feed on. House Raith, for example, feed on lust, and their weakness is love.
  • Magic of any type is disrupted by large amounts of water, especially running water. A villain once tied Harry up and kept him under a cold shower, rendering him helpless. Harry once got around this by swimming to the bottom of the lake he and his friends were about to drown in, sticking his hand in the mud at the bottom, and casting magic that way.
    • Word of Jim is that Listens-to-Winds can use magic despite the presence of large amounts of water, due to being a extremely powerful hydromancer.
  • Must Be Invited is also in play for ALL forms of magical creatures and human spell casters. Humans and "more human" creatures like White Court Vampires can cross the threshold into a home, however magical abilities cannot be used if entering uninvited. Purely magical creatures are unable to enter a home in this manner.
• In The Falconer, the traditional cold iron is useless against fairies. However, a special species of thistle is very effective. Which is why it is nearly extinct. The fae were very diligent about that.
• Crucial in The Reckoners Trilogy, where every super-powered "Epic" has a weakness that will either cancel out their powers or at the very least make them vulnerable to physical attack. Sometimes it's as straightforward as being close to a particular kind of metal, but others get crazier - like one who the characters mention could only be killed by people who are 37 years old. It's revealed in the second book that an Epic's weakness is related to their greatest fears and traumas. Sourcefield, for example, is vulnerable to Kool-Aid because when she was human her grandparents tried to poison her with it. Megan almost died in a burning house when she was younger, and therefore became vulnerable to fire upon her transformation.
• The Shade in Shadow of the Conqueror are vulnerable to sunstones, which burn their flesh on contact.
• In A Song of Ice and Fire, dragonglass is the main weakness of the Others. Sam Tarly was able to kill one by stabbing it with a dragonglass dagger. Legends say that they can also be killed by dragon steel (believed to be Valyrian steel), but as of the fifth book this has not been tested. Their Wight servants meanwhile can only be killed by fire or chopping them into little pieces (Removing the Head or Destroying the Brain is not good enough). Dragonglass does not work on them.
• Star Wars Legends got in on the act by having creatures who "pushed back" the Force (in the case of the ysalamiri), hunted with the Force (thereby making them far more aggressive around Force-users, as with the vornskrs), or who had been "severed" from the Force, and so were unable to be sensed or affected by the Force (like the Yuuzhan Vong). The idea was creating handicaps so that a simple kidnapping plot, for example, would work against Jedi, who would normally be able to shrug off drugs, sense someone walking up behind them, open locked doors, etc.
  • And there was the mighty lightsaber's weakness: the useless space-metal cortosis, which renders a lightsaber useless for a few seconds. Oh and for most you can't immerse them in liquids without the blade switching off. Rain's fine though, and Jedi from water worlds fix this problem with some modifications.
  • Lightsabers have another weakness as well. Bullet based weapons (called "slug throwers" in universe) can't be reflected by a lightsaber as blaster bolts can. All it does is melt the projectile, which means instead of a Jedi having a speeding bullet coming at their face, they have a piece of liquid metal coming at their face.
• In The Wheel of Time, people born with the potential to channel the One Power have two weaknesses that Muggles don't:
  • When consumed, the herb forkroot acts as a tranquilizer and temporarily prevents them from channeling. Becomes absolutely devastating when the Seanchan empire, which enslaves channelers with Restraining Bolts, finds out and starts using forkroot to cull its conquered cities.
  • A circle of thirteen channelers and thirteen Myrddraal can attack their minds directly, overwrite their personalities, and convert them into a minion of the Shadow.

Live-Action TV

• All That:
  • Parodied on the Nickelodeon sketch comedy show, where recurring character Superdude's weakness was "lactose intolerance", meaning in his case that merely being in the proximity of dairy products was harmful to him. Naturally nearly all of his opponents were dairy themed. Or would fight in an area where dairy products would be common. Such as a cow barn.
  • Another superhero, Bucketman, got his powers from radiative materials stored in a bucket that landed on his head. Problem was, he couldn't get the bucket off, and his blind attempts at heroism were often... less than ideal.
• Doctor Who:
  • The Doctor's sonic screwdriver was notorious for having no specific guidelines or limits to how it could be used, so much that lazier writers would rely on it too much as a Deus ex Machina to get the Doctor out of any predicament. The Fifth Doctor broke it in the Season 19 episode "The Visitation" and went without it for the rest of the Classic series. When the show returned in 2005, two very specific limitations were put on it: a), the screwdriver can't break through a Deadlock Seal, and b), "it doesn't do wood". The latter has been repeatedly lampshaded as "rubbish".
  • In the Series 2 episode "Tooth and Claw", the werewolf is allergic to mistletoe. The Doctor suggests that the monks who worship it may have conditioned this weakness into it, and at any rate the monks wear garlands of it to prevent it from getting any ideas. Likewise, Sir Robert's late father covered the library's walls and doors with mistletoe oil, keeping the wolf at bay for a while.
• Game of Thrones: The wights and their severed limbs will only stop moving if (A) they're set on fire, (B) are so thoroughly torn apart that their individual joints cannot move, or (C) are stabbed by something associated with super-fire, like obsidian or Valyrian Steel. In the White Walkers' case, the obsidian causes them to scream for a few seconds as it sinks in before they disintegrate, while the Valeryan steel causes them to instantly disintegrate. The Night King is immune to fire and can only be defeated with Valeryan Steel, but this comes at the cost of being the keystone to his entire army.
• On Happy Days, chopped liver is this to Fonzie. It nearly destroys his friendship with Richie, who wanted to use this as a newsworthy item in the school newspaper.
• Kamen Rider often uses this as the reason that costumed superheroes are needed to fight the villainous army of the year:
  • Kamen Rider Blade deals with humanity trying to survive the battle game of the Undead, who possess Complete Immortality and can only be defeated by each other, which seals them into playing cards. The Riders of the show use technology together with the cards to simulate being Undead themselves, allowing them to seal other Undead.
  • Kamen Rider Double has powers that come from the same source as the Fantastic Drug addict Dopants, allowing his finishers to break the Gaia Memories that they gain their superpowers from without killing them.
  • Kamen Rider OOO has the purple Core Medals act as this to all of the others. The other Core Medals are created to draw limitless power from human desires, while the purple Cores are created from the desire for nothing, allowing them to break the otherwise invincible Cores of the other colors.
  • Kamen Rider Drive has technology specifically designed to allow him to destroy the cores of the Roidmudes, shapeshifting androids who otherwise possess Resurrective Immortality. While there's nothing unique about Drive's technology in theory, the creator of it has good reasons for wanting to keep it in the hands of only trustworthy individuals.
  • Kamen Rider Ghost has essentially the entire plot driven by Edith trying to find the kryptonite for the Gammaizers, immortal androids that he created and now have his entire people hostage due to a programming oversight. Nearly every powerup in the show is one of his failed attempts to find something that will work, with what actually works being when the title character evolves from a ghost to a deity and gains new emotion-based powers.
  • Kamen Rider Ex-Aid deals with the outbreak of the Bugster Virus, a hybrid computer and biological virus that can only be excised from the patient using specialized medical equipment styled after video games.
  • Kamen Rider Zi-O deals with the Another Riders, monsters who copy the powers of the 19 previous Kamen Riders and can only be killed by the real Rider, except they've also replaced that Rider in history. Zi-O can use his own powers to gather the real Rider's powers that were lost to time and use them himself, making him the only thing that can defeat the Another Riders.
• For Sportacus from LazyTown, it's processed sugar like in candy; eating any sugary food renders him immediately comatose, and fresh fruit or vegetables are required to restore him.
• Riverdale: When Archie became Nigh-Invulnerable in Season 6, he finds out he loses his powers when he's around palladium and asks Betty to keep it away from him. This, of course, is used against him by the season's Big Bad. He later overcomes this weakness when Cheryl forged his skin to be impervious to palladium, but in the process he gains a new weakness: the daggers of Migido.
• Star Trek: Deep Space Nine has linear time for the Prophets/wormhole aliens, who are completely incoporeal and untethered to the flow of time like coporeal lifeforms are. At best, the concept of linear time simply confuses them, since they view the past, present, and future as being one and the same. At worst, they can be harmed by it: a Pah-Wraith possessing O'Brien's wife tries to coax him into firing a Chroniton Beam into the wormhole to kill the Prophets in "The Assignment", and Chroniton Particles are used to drive away a Prophet and a Pah-Wraith in "The Reckoning".
• The Thundermans: Thundertanium is a metal that's immune to superpowers, be it Hank's Super-Strength or Phoebe's telekinesis, rendering any attempt to use superpowers on it the same as a normal person attempting to punch or levitate a hunk of solid metal. It can't actively weaken any super, but every super prison makes liberal use of it to contain its superpowered prisoners.
• Non-super example: James May of Top Gear (UK) appears to have mild to moderate obsessive-compulsive disorder. His co-presenter Jeremy Clarkson once drove him offstage by rotating the bezel on his watch until it was out of alignment with the face.
• Cole on Tracker (2001) was vulnerable to Lodestone - it interfered with his life force sensing ability and weakened him a bit.

Mythology, Folklore, and Religion

• The Chinese tale of the Ten Brothers has ten brothers all born with supernatural powers that they lose when they come into contact with limestone.
• Traditionally Cold Iron (which may or may not be the same thing as regular iron) is this to The Fair Folk, serving both to drive them away (hanging an iron horseshoe over your door turns it into an impenetrable barrier to them) as well as being directly harming them (they cannot physically touch iron without being harmed, and iron weapons are the only things capable of killing them)
• Over the centuries vampires have managed to accumulate a truly impressive list of traditional kryptonite factors (rivaled only by that of squishy humans), to the point that most writers have to Nerf or outright ignore several of them to make vampires pose any sort of threat.
• Werewolves' best-known Kryptonite Factor nowadays is silver, though it's worth to mention that this actually is Newer Than They Think; the idea apparently originated from the Beast of Gevaudan, which according to the myth was killed by a silver bullet, but back then, the reason it succeeded in killing it was believed to be because the creature was of satanic origin and the bullet had been blessed. Before silver became iconic, werewolves' best-known Kryptonite Factor was Wolfsbane (also known as Aconitum), a plant people believed to have various effects on them, including killing them.
• The Norse god Balder was so greatly revered that every object, every element and every organism in the world vowed that it would never harm him, effectively making him invulnerable to everything... except for mistletoe, which was never required to make such a vow because it was thought to pose no threat. Three guesses as to how that turned out. An alternate version suggests that Frigg, Balder's mother, asked every creature on earth not to harm her son... but the Mistletoe is a parasite that grows on other trees, never touching the earth. (Or just because she forgot about it.)
• There's a fairly well known verse in The Bible, Book of Judges 1:19, which reads "The LORD was with Judah, so that they took possession of the hill country; but they were not able to dispossess the inhabitants of the plain, for they had iron chariots." Which would seem to imply the God can't defeat iron chariots. Some people have explained it as saying it was Judah who failed rather than God. While this interpretation is valid, it raises further questions, as it implies that having an omnipotent God on your side is somehow less of an advantage than having iron chariots. This is because the ancient Hebrews didn't all believe that god was omnipotent, only superhumanly powerful.

Tabletop Games

• The Ravenloft game setting's Van Richten's Guides not only expanded on a lot of creepy D&D monsters' powers, but also gave plenty of them unique Kryptonite Factors of their own. We're not talking about the usual Vampires Hate Garlic stuff; in Ravenloft, even golems have their own personalized Kryptonite, which players have to figure out if they're going to use it against the baddies.
• Vulnerability and Weakness are used to represent this in GURPS.
• A rather spiteful example in Warhammer 40,000 with the Grey Knights Space Marines, Magitek Super Soldiers that comprised the fighting arm of the Ordo Malleus, also called the Daemonhunters. Back in 3rd edition and earlier, Daemons were generally pretty rare but powerful shock troops that were small auxiliary subsets of other armies, like the Eldar with their Avatar and the Chaos Marines with their Chaos Daemons. One usually wouldn't fight an all-daemon army, and if an all-daemon army ever was fielded (usually by the Munchkin, given that this was a major Game-Breaker back in the day), it usually was by the player's choice. So if you spammed Daemons and came up against a Daemonhunter player, you were just getting your well-deserved comeuppance for fielding a cheap army. But then Games Workshop went and split the Chaos Marines from the Chaos Daemons into two separate books in one of the most maligned decisions in the history of the hobby (which is saying a lot!), and suddenly you had a faction who fell prey to another army almost by virtue of the other army showing up.
  • As of April 2011, the Grey Knights themselves were given their own book to replace the Daemonhunters Codex. They're still insultingly effective against Daemons, if not more so. They just got better against other armies.
    • Grey Knights have more or less became the Elite Mook of the Imperial forces, rather than a dedicated Daemonhunting branch. However they still have a horrendous number of special rules against Daemons and it's even possible to statistically destroy 33% of a Daemon player's army before the game even starts, and that's without tailoring. Before these rules came with an additional rule that benefitted Daemons, to balance out the power. It's gone now.
• Mutants & Masterminds has the Vulnerability and Weakness drawbacks.
  • The official adventure module, Time of Crisis adds a weakness to the Big Bad Omega in the form of the cosmic detonator rods you've been pulling from the various Cosmic bombs which will completely bypass all of his defenses, potentially turning the final battle into a curb stomp.
• Essentially required of characters (including NPC monsters) with superhuman toughness and/or regeneration in The Dresden Files. Something — referred to as "the catch" — must exist that bypasses their defenses, and common and/or obvious catches can provide point cost breaks. (Obscure ones like Nicodemus's vulnerability to his own Judas Noose are okay, too, it just means paying the full cost.)
• Given the origin of the trope, any superhero RPG has a version of it. Champions for example provides both Vulnerability (where certain attacks are more effective) and Susceptibility (where just exposure to the offending factor is enough to cause ill effects), plus the option of applying Limitations to powers so they become cheaper but for example don't work under all circumstances or against certain things.
• Lead is extremely poisonous to Europans in Rocket Age.
• Most supernatural creatures in New World of Darkness have a vulnerability to some substance, which causes aggravated damage to them:
  • From the core rulebook, all ephemeral entities have a unique Ban and Bane. The Bane is a substance or energy that is anathema to the entity, and grows more specific the higher the entity's Rank (so a minor Rank 1 ghost might be burned by salt, while the Rank 5 ghost of an ancient necromancer called back by a cult might only be vulnerable to an obsidian dagger inscribed with the name of a god of death). The Ban, on the other hand, is an act the entity must perform or not perform under certain circumstances, and grows both more esoteric and more significant as the entity's Rank rises (so a Rank 1 spirit of fire might be unable to cross running water, while the Rank 5 spirit of a certain volcano might be required to use its powers to assassinate anyone named by someone who drops a kilo of solid platinum into the volcano's caldera).
  • Vampire' are fire and sunlight. To a lesser extent, stakes are effective too, though that one merely leaves them paralyzed rather than causing any kind of special damage.
  • Werewolves' is, as usual, silver. In-universe, this is explained by Luna, the Moon Spirit, cursing them with this weakness as a punition for killing their progenitor Father Wolf. Because of this, the Forsaken (those who acknowledged their crime and are trying to atone for it) have it slightly less rough and are merely harmed if the substance gets in their blood, while the Pure (those who refused responsibility for the crime) can't even touch it without getting hurt.
  • Prometheans' is fire as well, though they can heal from electricity as a compensation.
  • Changelings use Cold Iron against their enemies, the True Fae. Powerful Changelings gain "frailties" as the storybook logic of faerie magic takes root within them; for example, the Summer King of Miami is harmed by the touch of copper and can't rest in a room without open windows.
  • Mummes' are fire and relic weaponry.
  • Beasts have an interesting variant; while they don't have any Kryptonite Factor in their natural state, Heroes possess an ability known as Anathema, which allows them to force one on them. It's commonly believed among Beasts that vampires are vulnerable to fire because their Progenitor was a Beast who suffered an Anathema giving that weakness.
  • This extends to fan supplements as well:
    • Geniuses themselves aren't particularly vulnerable, but all their inventions go completely haywire when exposed to actual scientific scrutiny, including being handled by a mere mortal.
    • Leviathans' are electricity, Virtue, and the Symbol of Marduk.
    • Dragons' is Jadeite. The retooled Dragon Rekindled makes them vulnerable to dark magic and regular jade as well, albeit not to the same level.
    • Princesses aren't vulnerable to any material substance, but they do have a form of enhanced empathy called Sensitivity, which causes them to feel hurt when they see people commit cruel or vicious actions. This can variably cause physical injuries, headaches, depression, anger or denial, and has the side effect of creating "shadows" which disturb their ability to transform.
    • Their main opponents, the All-Consuming Darkness, has a distinct vulnerability to jade, which burns its minions by mere contact.
    • Sirens are vulnerable to pollutants and chemical weapons.
• Old World of Darkness: Vampires and werewolves have the same weaknesses as in NWoD, while changeling are weak to Cold Iron.

Theater

• The Toxic Avenger musical makes bleach the only thing that can kill Toxie. Luckily filthy Hudson water can resurrect him.
• Tough Man from Eugenius! is allergic to love so his sidekick Super Hot Lady can never have him. Though he is implied to be gay at the end.

Video Games

• MMORPG Example: In City of Heroes, one can unlock the "Kheldian" Epic Archetype, a form of Energy Beings from outer space that have merged with humans. Though they possess a greater arsenal of powers than "ordinary" heroes, as well as the unique ability of shapeshifting, they also possess a fatal weakness to a particular form of Quantum Energy. Thus, while playing or teaming with one, enemies wielding Quantum Array Guns are mixed in randomly with the ordinary enemies — as are the lethal "Void Hunters", mercenaries specifically trained to hunt and kill Kheldians, adding implants that protect them from Kheldian attacks to their Quantum Array Guns.
  • This weakness was toned down due to years of player complaints as the Quantum Weapons were considered to be too commonplace for such a powerful attack. Now the quantum weapons deal less damage and only stun the player for a fraction of a second rather than taking over a third of their life and leaving them stunned for too long to defend themselves.
  • Having a Kheldian on the team will occasionally spawn Shadow Cysts that spawn spirits that ruin accuracy and attack speed of everyone on the team. Oh, and they explode when destroyed. And they're surrounded by Mooks who will probably kill you because you can't aim or fight back. For the most part, Shadow Cyst = Total Party Kill. Thanks Kheldians!
  • To add insult to injury, Kheldians aren't really particularly overpowered. They're actually pretty lackluster in comparison to the other archetypes, at least without a whole lot of work and expense tricking out your build.
• The Dragon spell from the PLATO computers dnd game has no effect on normal enemies, but it instantly kills the dragon Final Boss.* Haar in Fire Emblem: Radiant Dawn is an otherwise One-Man Army mechanically, but (also mechanically) is always 2 hit killed by thunder mages.
  • This applies to almost every unit with a weakness in the Fire Emblem games: Attacks with a weapon the target is weak to (this is distinct from the sword>axe>lance>sword thing) triples the weapon's "might" stat. And pray you don't get unlucky enough to get hit by a critical hit by your weakness.
• In The Elder Scrolls V: Skyrim, draconic Big Bad Alduin is completely invulnerable unless under the effects of the "Dragonrend" Thu'um shout. Dragonrend is the only Thu'um shout created by mortals, and it forces the immortal dragons to experience mortality, an utterly disorienting concept to them.
• Final Fantasy Crystal Chronicles: Echoes of Time: The hero's crystal fragment triggers Veriaulde's transformation and harms Larkeicus, in both cases causing their bodies to smoke or steam.
• The Legend of Zelda:
  • In games like The Legend of Zelda: A Link to the Past, only the Silver Arrows and the Master Sword can harm Ganon.
  • In The Legend of Zelda: Ocarina of Time, you cannot finish off Ganon with the Biggoron Sword; he must be defeated with the Master Sword.
• In Mega Man, all enemies have this. An extreme example is Metal Man from Mega Man 2, who dies in 1 hit from his own weapon (on Easy. On Hard mode he takes 2 shots).
• Runescape lets you create Kryptonite in the form of Bane Ore. This stuff can be tuned to various creatures, and doing so will make it harmful to them. Bane Metal can then be made into arrows and bolts. Balmung, the axe you use to slay Dagganoths during a difficult quest, is revealed to be made of Bane Metal as well.
  • The Vampyre Quest series brings us Silverthril, an alloy of mithril and silver, which is somewhat effective at slaying immortal Vyrewatch. Later on, weapons crafted from the Blisterwood Tree take this up a notch.
• In Scribblenauts, a few creatures are impossible to kill except using some special objects:
  • Vampires can only be harmed by crosses, stakes, garlic, sunlight and anything with the adjective Holy. Using any of those will instantly slay the vampire (yes, even throwing a clove of garlic to him), but there are useless or very weak weapons against any other foe.
  • Ooze can only be killed with fire.
• In South Park: The Fractured but Whole, the player character is forced to choose a Kryptonite in the form of an enemy faction that they'll have penalties against due to the rules of the superhero game that the kids are playing. Each of the other playable characters have Krytonites listed on their character sheets, though it typically just serves the purpose of a gag. Coincidentally, Cartman (who made the rules in the first place) is the only character who doesn't have a listed Kryptonite.
• In Tears to Tiara and the sequel Tears to Tiara 2, non-humans on your team are affected whenever the bad guys use Obelisk to unleash the "holy" aura Gravitas.
• 20XX, which is heavily inspired by Mega Man X, has the same kind of boss weakness cycle. Some of them make sense: the shield-focused Vile Visage is vulnerable to shield-breaching mortars, and the engineered plant Death Lotus can be trimmed with spinning blades. Others are a bit stranger; minigun-encrusted Perforator Alpha is susceptible to a slow-moving phasing projectile for reasons that are never quite explained.

Web Animation

• Happy Tree Friends: Being an Expy of Superman, Splendid has kryptonut in one episode, which is kryptonite shaped as an acorn. Exposure to the radiation from it causes him to lose his powers and fall ill with what resembles the stomach flu. At the end of the episode, he crushes the kryptonut and accidentally inhales the powder, causing him to vomit uncontrollably as the skin on his face falls off. This (and another instance confirmed by Word of God) is the only time he has ever died, as nothing else can hurt him.
• RWBY: Most humans aren't consciously aware of magnetism and Pyrrha can only affect people with her Magnetism Manipulation power if they're wearing metal. Penny, however, is a robot that is made from a magnetic material. During the Vytal Festival tournament, the villains deliberately rig the fights so that Penny will be forced to fight Pyrrha to deliberately invoke this weakness. When they trick Pyrrha into using her full power, Penny and her sword wires become so badly entangled by the force of the magnetic pulse that she ends up being torn to shreds by her own weapons.
• Suction Cup Man: It becomes a recognized fact that "No one can kill Suction Cup Man", look at him go. That is, up the outer wall of a tall building. However, when the hapless Business Guy specifically makes him fall off the building with a spray bottle of deliberately produced "Anti-Suction Cup Cleaner", he doesn't just fall off the building, he dies before the minute is out and becomes roadkill. The rest of the video centers around him going to Hell — where over the Devil's protests, Suction Cup Man just does that thing he does.

Webcomics

• Aberrations in El Goonish Shive are difficult to harm using physical attacks, but are weak against magical weapons, to the extent that a Hyperspace Mallet not normally capable of causing any real harm becomes a useful weapon against them.
• The Pa'anuri from Schlock Mercenary are immune to attacks by baryonic matter (that is to say, 'normal' matter) because baryonic and dark matter does not interact outside of gravity. Teraporting, meanwhile, disrupts their equivalent to biochemistry^note teraporting in the Schlockiverse creates billions of tiny wormholes, which are gravitic events and is toxic to them, meaning that fighting Pa'anuri involves saturating areas with Teleport Interdiction fields or rapidly teraporting in their vicinity. In the final arc, The Fleetmind invents a Teraport Gun which weaponizes this factor: it's not made clear what its effect would be on a baryonic opponent, but it is extremely deadly to Pa'anuri.

Web Original

• In the superhero spoof Adventure Game The Frenetic Five versus Strum und Drang, the character Pastiche has various powers, the most notable of which is an ability to become intangible. Her only weakness: she can't phase through rope.
  • In the sequel, The Frenetic Five vs. Mr. Redundancy Man, Lexicon, the character with a superhuman grasp of the English language, is incapacitated by poor grammar.
• In Tales of MU, the half-demon Mackenzie may be partially invulnerable, but crossing yourself is the only thing needed to repel her. In peoples of faith, this actually pushes her away and causes unbearable pain.
• Incredibly powerful mage Fey in the Whateley Universe is indeed one of The Fair Folk, and so she has a weakness to cold iron. And synthetics, which give her really nasty rashes. She has wardrobe problems because of that one.
  • Anyone who is able to use Erebeal Magic (one of the forms of Casting a Shadow in-universe) develops a negative reaction to the herb moly. Nacht, who was dipped into the Erebos as an infant and not expected to survive, but did, has this to a crippling degree, but fortunately for her, real sacred moly is exceedingly rare.
  • Played with by Phase, who's managed to slip a fake Kryptonite Factor into her official file. For the record, it's "dark chocolate administered orally".
• Upon entering melee range of any anti-dragon Noble Phantasm, Uther from Fate/Nuovo Guerra suffers a rank-down for all of his stats, in addition to any damage bonuses they have against him.
• How to Hero discusses this in the entry on weaknesses.

Western Animation

• In American Dragon: Jake Long, dragons can't stand Sphinx hair. Small amounts force them back into human form, while large amounts inflict serious pain upon them.
• In Avatar: The Last Airbender, earthbenders can't bend metal (until Toph discovers how). In The Legend of Korra, metalbending techniques have become widespread, so the new kryptonite is platinum. Metalbending works by bending impurities within the metal, and platinum doesn't have enough impurities to bend.
  • Most of the Bending arts have some hard counter that can be used to imprison troublesome Benders, usually by denying them access to their element in some way or another. Earth has the aforementioned metal (which can still be effective since Legend of Korra noted that only a few Earthbenders have the skills needed to become Metalbenders), and Earthbenders have also been shown to be useless when put in wooden containers. Firebenders and Waterbenders are vulnerable to extreme cold and heat respectively, and since they draw their powers from the celestial bodies eclipses can also shut them down for a short time. Air is the only one without an expressed weakness, but a few heavy chains or a straitjacket are usually enough to keep an Airbender from going anywhere.
• Captain Planet has a very odd weakness in that it's pollution, the very thing he's trying to fight. It'd be like Superman deciding to specialize solely on kryptonite cleanup duty.
  • His Evil Counterpart Captain Pollution, is weak against pure wind, water, earth, and fire while being composed of concentrated pollution. This makes it interesting in that they're walking kryptonite to one another.
    • Captain Planet was also shown to be weak to intense hatred in at least one episode. Adolf Hitler managed to completely disable him just by glaring at him. However, hate is regularly shown to be the pollution for Heart as even one of the rings used to summon Captain Pollution was Hate which was the negative copy of the Heart ring.
• Danny Phantom:
  • Danny is weakened by a flower called Blood Blossom. It removes his powers while causing him extreme pain. Plus the various weapons his parents and Vlad have devised that can remove his powers or hurt him while he is intangible.
  • Ectoranium, introduced in the Series Finale, is a green glowing rock that ghosts can't touch without being painfully shocked (in fact, it's the key ingredient in most anti-ghost weapons and defensive technology); they can still phase through it, which is an important plot point. Kind of an obvious Expy of Kryptonite, but in this case the Ectoranium is as much of a danger to humans as ghosts since it's a large asteroid that got knocked off course towards Earth.
• Specifically parodied in one episode of the Earthworm Jim animated series. Jim is helpless against the substance known as Wormtonite (which Peter Puppy claims they found at the back of the fridge, and might once have been cheese). Bizarrely, its effects include turning Jim into a bowl of candied corn.
• On The Fairly OddParents!, fairy magic has no effect on butterfly nets, which, therefore, are one of if not the only object capable of trapping them.
  • Genies are affected by a substance called smoof. What smoof is goes unexplained, but it's consistently purple.
• Spoofed in an episode of Freakazoid!, in which bad guy Guttierez tries presenting a variety of weaknesses (the color yellow, water, and kryptonite itself), failing each time, as Freakazoid points out that that's some other iconic character's weakness.
  • Freakazoid himself has two rather obscure and ridiculous weaknesses, though: he can be imprisoned in a cage with graphite bars charged with negative ions, and he has an aversion to "poo gas".
    Freakazoid: Dumb, dumb, dumb! Never tell the villain how to trap you in a cage!
    Guttierez: You probably shouldn't have helped us build it, either.
    Freakazoid: I know! Dumb!
    • Though as Guttierez pointed out, no one likes "poo gas".
• In a Bad Future segment on The Grim Adventures of Billy & Mandy, rebels led by Irwin use frogs as weapons, as they've learned that they are giant worm/planetary tyrant Future Mandy's Kryptonite Factor. They're wrong, as Mandy had leaked that information herself.
• The Hero Elementary episode "Sara Loses Her Snap" reveals that Sara Snap loses her powers for a day when she eats coconuts as shown when accidentally eating a coconut flavored power bar. This becomes a problem when the team has to move a giant hamburger out of the way.
• On The Mighty B!, Bessie (who fancied herself a would-be superhero) once tried to find her Kryptonite Factor by going through every food item she could think of alphabetically. By the time she got to zucchini she was so full that she became violently ill, and thus thought that zucchini was her weakness.
• In My Little Pony 'n Friends, Grogar is incredibly powerful and seemingly nothing can hurt him, but once a certain bell is rung, he is automatically banished back to the Shadow World.
• In the season 6 finale of My Little Pony: Friendship Is Magic, Thorax reveals that Queen Chrysalis has a throne carved from an ancient dark stone that absorbs all forms of magic that get too close to it except for changeling magic. Not even draconequus magic can resist it.
• Ninjago: The Ninja's Elemental Powers can be neutralised by a mineral known as Vengestone.
  • In Seceets of Forbidden Spinjitzu: Ice (Season 11 part 2), this is also one of the many properties of the Ice Emperor's corrupted ice.
• In The Powerpuff Girls (1998); the titular girls lose their powers if they come in contact with Antidote X.
• In Composite Santa's first appearance on Robot Chicken, half of his body melted after a fireball destroyed another enemy. He exclaimed, "Temperatures over 32 degrees Fahrenheit! My only weakness!" This later became a Mad Libs Catchphrase as "My only weakness" included bullets, water, and baseball bats.
• Aku from Samurai Jack is immune to all forms of damage except divine magic, so the gods created a magic sword forged from the righteous spirit of a Japanese Emperor to kill him. When that didn't stick, the Emperor had his son trained up to finish the job and eventually, he succeeded.
  • As a bonus, the sword cannot harm an innocent when it is in the hands of evil, so Jack himself can't be hurt by the weapon if it is used by a villain, as demonstrated when Aku once tried to stab him with the sword and it just bounced off.
• The Simpsons: Bart once discovered Principal Skinner's allergy to peanuts, and used it to practically enslave him. Skinner soon learns that Bart has an allergy too; shrimp. They end up in a "sword" fight with sticks with their opponent's kryptonite on the end set to "Duel of the Fates".
• The Sushi Pack are weakened by heat, and since they have a tendency to announce it, their most recurrent villains usually keep a couple of heat lamps around.
• Teenage Mutant Ninja Turtles (1987) parodied this in the episode "Michelangelo Meets Bug Man". In it, Michelangelo finds Bug Man, who turned into the superhero when he got angry, wrapped in chains that were laced with his main weakness before being thrown down into the sewer. His weakness? "Leestanite"! ^note The name is not an accident: it was a play on famous comic book creator Stan Lee.
• ThunderCats (1985): The ThunderCats are vulnerable to "thundrainium", a rare mineral that is a poorly-disguised knock-off of kryptonite. It even hurts Jaga, who is a ghost. For unexplained reasons, the villainous ThunderCat Grune the Destroyer is not affected by thundrainium, which makes him very dangerous as his mace is made of it.
• Tiny Toon Adventures: In an episode spoofing the Superman Film Series, "Super-Babs" was weak to carrot cake — she couldn't stop eating it, and the villain continued feeding it to her until she was too overweight to fly after him.
• Haggarium drains the power of Voltron in Voltron Force, as well as its component lions.
• WordGirl loses her powers and gift of perfect vocabulary when exposed to lexonite, a radioactive mineral from her home planet.

Real Life

• Aspirin is kryptonite to cats. This article even acknowledges the trope.
• Chocolate to canines. While it is much less known, chocolate is dangerous for cats too, though cats are much less likely to eat it than dogs are.
• Any human with a severe food allergy. Peanuts are a frequent culprit here, with some unlucky folks unable to be in the same room as peanut products without going into respiratory shock. Diabetics have a similar reaction to sugar.
• Salt to snails/slugs.
• Freshwater fish in saltwater and vice versa due to osmosis.
• The New England Patriots and Bernard Pollard. Pollard has destroyed the Patriots so many times that his fan nickname is the "Anti Patriot" and the "Patriot Killer". Pollard is a good player and is generally well-regarded, but it's bizarre coincidence that Pollard has done the biggest damage to the Patriots.
• Tin foil for microwave ovens.
• Norbormide is a rodenticide that is highly toxic only to rats and mildly toxic to all other animals.
• Diatomaceous earth to insects.
• Reporter Richard Morgan recounts that a guy he was interviewing parodied this in real life.
  "But that bio – I keep meaning to fix that bio, because one time I interviewed a guy, an archaeologist, and he slam-dunked a giant pineapple onto the table when I first started the interview, and he waved it in front of me. My bio says, “Pineapples are his weakness.”"
  Interviewer: "I assumed that meant you loved them."
  "Yeah, I would probably eat anything with pineapple on it. But he sort of waved it around as if it were kryptonite and made a joke about it. It was weird and awkward and made me think I shouldn’t put that much information about myself out there."

---