Takes One to Kill One

Ah, the classic vampire weaknesses: sunlight, garlic, silver, and another vamp's fist through your skull.

"Magic must defeat magic!"

— Uncle, Jackie Chan Adventures

In many works of fiction, there are creatures that are Immune to Bullets, Made of Iron, and in worst-case scenarios have no Kryptonite Factor. Even nuking them has no effect. But fear not, for while these creatures may be immune to fire, bullets, nuclear weapons, and MTV, these monsters still have one weakness... Themselves, or their own kind.

There are ways of how this is accomplished:

• Stop Hitting Yourself: It is one easy way to do this - you don't have to find something similar when you can use their own body/projectile/whatever to hurt them.
  • Carrying the Weakness: If you can manage to make said enemy drop their own weapon/body part/whatever, you can use it to hurt them easily.
• Menace vs Menace: Another one of their kind can stop them.
  • Heroic Menace vs Evil Menace: This is often used as a justification to why the heroes, who either are this kind of monster/alien, can turn into one, or have one under their control, can seriously wail on the Monster of the Week, and yet the military forces and police are still useless — though if this becomes a trend, it may lead to other characters being unable to affect the plot in a meaningful way or even turn those connected to the monsters into a Spotlight-Stealing Squad. If the heroes are forced to become this type of monster to win, expect a My God, What Have I Done? moment afterwards.
  • Menace Civil War: If the monster is unaffiliated with either side, it can lead to Always a Bigger Fish (or A Same-sized Fish in this case). Occasionally, the heroes may trick the two monsters into fighting each other.

Sub-Trope of Mutual Disadvantage. Super-Trope to Magic Must Defeat Magic. The opposite of Tactical Rock–Paper–Scissors where each type of combatant has some other capable of curb stomping it. However, this can be a subtrope of Elemental Rock-Paper-Scissors if an element happens to be weak against itself. Compare Beat Them at Their Own Game, Hoist by His Own Petard, and Summon Bigger Fish. Contrast Like Cannot Cut Like and Counterpart Artifacts. May be a reason one becomes a Hunter of His Own Kind. See also Serial-Killer Killer, which usually doesn't involve the supernatural.

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Examples:

Anime and Manga

• After God: The only thing that can harm an IPO is another IPO, which is why the Institute focuses on getting one of them to ally with humanity while breeding one of their own.
• The Imperial Weapons from Akame ga Kill! are guaranteed by fate to kill the user's target- unless said target also has an Imperial Weapon, in which case the resulting battle is certain to end with at least one user's death. At least that's how the saying goes, as there's at least one occasion where multiple Imperial Weapon users were fighting and no one died: specifically, Akame and Kurome's final fight in the manga, thanks to intervention from Wave even with Tatsumi trying to stop him from getting in their way.
• Attack on Titan is a complicated example. First there is special gear used to fight titans. It is definitely possible to kill titans in this manner but there is often a large death toll. Then it's revealed that the only thing that can reliably hurt a Titan is another Titan. Which makes the Titan Shifters extremely valuable allies. The gear used by normal humans is much more limited in application and effectiveness in comparison. For example, Eren doesn't kill a single titan while in his human form for the entirety of the first season, but in Titan form he's brutally effective and even out-fights the dreaded Armored Titan in hand-to-hand combat.
• In Baccano!!, the only way an immortal can die is to be absorbed by another immortal.
• In The Big O, one of the few things that can damage a Megadeus is another Megadeus, though this is less an issue of compatibility than a matter of sheer firepower. There have been several organic threats that could have legitimately beaten a Megadeus.
• Ryo Takatsuki's nanite-powered Superpowered Evil Side in Project ARMS has a unique power to negate the Healing Factor of other ARMS.
• Bleach: Baraggan is resilient enough to withstand a Fantastic Nuke with only minor injury and can unleash an unstoppable, infectious wave of decay at will. He's killed by teleporting an infected hand into his body, where his own power rots him into nothingness.
• Blood: The Last Vampire has this as its basic premise.
  • Same goes for its spin-off series Blood+. Chiroptera will regenerate from basically any wound. Only the blood of an opposing queen can put them down. Same goes for everything else spawned by that Queen, and the Queen herself for that matter.
• In Claymore, the eponymous warriors are humanity's only hope against the yoma — because they are infused with yoma blood to gain control over yoki, their demonic energy. On the flip side, all Claymores run the risk of turning into super yoma, a.k.a. Awakened Beings. However, the beings the Claymores were really meant to fight are the Dragon-people whose flesh is the source of yoma.
• Digimon Adventure: MetalEtemon effectively has Nigh-Invulnerability when he is met as not only is he a Mega-level Digimon, but his entire body is coated in Chrome Digizoid, the hardest substance in the entire world. Zudomon was able to leave a crack on his body when he threw his Vulcan's Hammer at him as the hammer is also made out of Chrome Digizoid, allowing him to be killed by SaberLeomon.
• Dragon Ball:
  • King Piccolo was utterly invincible to any human who didn't know the Evil Containment Wave, which kills the person who uses it. Only Goku manages to outmatch Piccolo and later his son Piccolo Jr. They are both aliens sent to Earth to save their lives.
  • When they were introduced, the Saiyans were so overwhelmingly powerful compared to any enemy that the Earth had ever faced that even after a year of training, the Earth's fighters can't even take down Nappa, who is far weaker than Vegeta. Only Goku and Gohan were able to turn the tides and repel the Saiyans, and Goku is a Saiyan and Gohan is a Saiyan hybrid.
• The plot of Eternal Sabbath revolves around getting Shura to kill Isaac, as Shura is the only one who understands Isaac enough to stop him.
• In Fairy Tail, the only magic that can even scratch Dragons is Dragon magic. Dragon Slayers are simply humans who wield the same kind of magic as Dragons. The only exception to this are Demons who rely on "Curses" which are fundamentally different from magic. Even then, the Dragon struck by the Curse was already dead, being a spirit.
• In some continuities of the Gundam franchise, Gundams are defined by using a technology that makes them leaps and bounds above any previously existing weapon. (In others, Gundams are just one advanced form of mobile suit, if they even had a commonality beyond name, which can be equaled or surpassed by others.)
  • The director of Mobile Suit Gundam SEED outright said that "Only a Gundam can beat a Gundam" was part of the series' design philosophy. In this case, it was aided by the fact that most Gundams use Phase Shift Armor, which is immune to physical damage, meaning that only beam weapons can hurt them. Gundams themselves are also the first suits to have beam weapons, which are otherwise mounted on ships, making them too slow to be effective against agile mobile suits. It's not until late in the series that miniaturized beam weapons are suitable for mass production, and even then the Gundams have defenses against them (albeit less comprehensive than their defense against projectile weapons) that ordinary mobile suits lack.
  • In Mobile Suit Gundam 00, Celestial Being's Gundams are several orders more advanced than the forces of Earth's militaries, particularly in their use of the GN Drive solar furnace which grants nigh-infinite power. At one point all three of the world's superpowers devote nearly their entire armies, including specialized anti-Gundam units with souped-up mobile suits and the most elite pilots, just to take down Celestial Being's four guns. The best they can do is constantly attack the Gundams until their pilots are exhausted by the nonstop fighting; the machines themselves are completely unharmed. Their strategy collapses when three more Gundams, whose existence was completely unknown before, show up on the battlefield. Late in the first season, the Earth forces are handed a supply of GN Drives and a mobile suit designed to use them, which results in their finally being able to fight the Gundams on equal footing. By the time of the second season, the new Earth Sphere Federation has mass-production machines that outclass the original four Gundams in a straight fight...which, conveniently, is when the Mid Season Upgrades roll out.
  • Gundams in Mobile Suit Gundam: The Witch from Mercury are suits with a "Permet" Brain/Computer Interface that grants incredible reaction times and an overwhelming swarm of Attack Drones. Their GUND format would have become the standard decades earlier if the damage they do to their pilots hadn't gotten them outlawed. After Elan piloting the Gundam Pharact soundly defeats Guel, an Ace Pilot in a non-Gundam Ace Custom, he states that only a Gundam can defeat another Gundam. We're only shown to the contrary when a Gundam is heavily outnumbered and/or faces an anti-Permet Power Nullifier—and Gundams can outright ignore the latter by increasing the intensity of its system, although this puts a potentially fatal strain on the pilot. Even among Gundams, however, Gundam Aerial specifically has overcome the limitations and drawbacks of the GUND format, putting it in a class of its own — at its maximum potential, not even another Gundam can defeat it.
• Played With in Hellsing where almost everyone constantly thinks that in order to kill a monster you either need a monster or to somehow become a monster. By contrast, Alucard, the biggest scariest monster around, thinks the only thing that can truly kill him is a human. This is because he got his ass kicked by Dr. Abraham Van Helsing in his backstory.
• Heroic Age: All Nodos are so exceedingly powerful that the only thing that can fight a Nodos is another Nodos. Anything else is certain to get curb stomped. Even then, battles between Nodos can go on for quite a while. At one point, a Nodos battle lasts for 300 hours straight.
• Holy Corpse Rising: Nikola points out to his peers that it is pretty much impossible for a regular human to fight a witch. To defeat them, they need witches of their own.
• In JoJo's Bizarre Adventure, a Stand zig-zags this with the ways it can be harmed. A Stand is a telekinetic construct of its user's spirit, usually Invisible to Normals, and can only be harmed by another Stand (which also inflicts similar damage on its Stand User). However, a Stand User is just as vulnerable as normal people to being killed by conventional means, such as guns or swords; killing the Stand User will also destroy the Stand. Then there's how the spirits of Ghost Girl's Alley in Morioh are able to flat-out grab and destroy Stands by ripping them apart (as shown by how they destroy the Stand Killer Queen and Kira's spirit suffers a similar fate thanks to synchronization), though this might still technically count since Stands are spiritual-based and technically 'ghosts' themselves.
• In Naruto: the jinchuriki of the Ten-Tails are immune to all ninjutsu, since the Ten-Tails is the progenitor of all chakra, and its power is virtually the same as the Natural Energy of the world itself. However, this also means that Sages, who amplify their techniques with Natural Energy to use senjutsu, are able to harm them.
• Neon Genesis Evangelion: The Evas who are pretty much Angels anyway are usually the only things on Earth that can fight an Angel and win because only they can break the Angel's AT fields. To be more accurate, Angels project AT fields so strong that only the similarly-sized Evangelions possess the power necessary to breach them. There are cases where the Evas weren't directly responsible for the victory. One was beaten by blowing up a destroyer in its mouth, Ramiel was taken down by a positron cannon fed with the entire country's power supply (wielded by an Eva, but the cannon did the work). Certain other options exist to hit the 180 million megawatt figure stated to be necessary to overcome Ramiel's AT-Field, which was one of the strongest of all the Angels (behind Tabris and Zeruel, most likely). The largest nuclear devices, for instance, could likely knock out an Angel, though nuking them isn't exactly an ideal solution.
• One Piece: About eight-hundred years ago, an advanced precursor civilization had in their possession three incredibly powerful superweapons. One of these was the Pluton, the mightiest battleship ever constructed, able to obliterate an entire island in a single blast. Only one was made, but the shipwrights retained the blueprints and secretly passed them down over the centuries just in case the Pluton fell into the wrong hands and a second Pluton would be needed to counter it. Franky is forced to burn the blueprints to keep them from being captured by the World Government. He admits that this means they now have no way to counter the Pluton, should it ever be found and unleashed, but it was better than the World Government being able to construct an endless armada of nigh unstoppable superweapons.
• Puella Magi Madoka Magica seems to play with this trope. At first, the Magical Girl magic appears to be the only way to kill Witches (straight trope), but it is eventually revealed that Akemi Homura actually uses firearms and bombs (subversion) to kill Witches off, because of her comparatively weak offensive powers. And then, in episode 11, she blasts Walpurgis Night with literally thousands of explosions and doesn't even manage to scratch her (keep in mind she usually manages to kill witches off with barely one hundredth this firepower). For all intents and purposes, it turns out Walpurgis Night can't be stopped by either firepower or magic, and the only reason she is defeated is the Reality Warper power of Madoka's wish which causes a Cosmic Retcon to erase all witches from existence altogether (thus, double subversion).
  • It is possible to stop Walpurgisnacht, but it takes a large group of magical girls and they are all but guaranteed to sustain catastrophic casualties. Considering that Homura unleashes an army's worth of ammunition on Walpurgis to no avail while regular magical girls tend to use much less impressive amounts of firepower, it is possible that Walpurgisnacht is weaker to magical weapons, but just enough to turn the battle from "impossible" to "just barely doable".
• A variant is used in Tokyo Ghoul. Ghoul Investigators hunt Ghouls using a weapon called a Quinque, which is made using a Ghoul's kagune. The audience learns this when Kureo Mado brings out his Quinque to kill Mrs. Fueguchi, who recognizes it as having been made from her husband. Later on, he brings out his newest Quinque to attempt to kill her daughter — he had it made from Mrs. Fueguchi after killing her. However, this is the most effective way of fighting ghouls available to humans. They could, theoretically, beat them to death with their bare hands, but ghouls have a physical edge in that area.
• In Yu-Gi-Oh! ZEXAL (both, anime and manga), the Numbers monsters cannot be destroyed in battle except against another Number. Subverted in that they can still be destroyed by card effects, and it's entirely possible to negate their invulnerability so that they can be destroyed by any monster.
• Invoked in YuYu Hakusho by Kurama when he and Hiei fight against a robot made of an "indestructible" metal. Kurama leads its stretchable claws to crash into each other, which breaks the metal apart and allows him to destroy its exposed internal components.

Comic Books

• The Boys: The Homelander is basically Superman with none of Superman's positive traits. In order to make sure they could control him, Vought apparently raised him next to a nuke, and cloned him, raising the clone for the sole purpose of taking out the Homelander so as to have a loyal equivalent in case of betrayal. Unfortunately, the clone (Black Noir), being unable to carry out the mission it was created for, took matters into its own hands by filming itself committing atrocities so the Homelander would think he'd committed them. When the Homelander finally snaps, rebelling and killing Vought's puppet president, Black Noir finally gets to intervene.
• B.P.R.D.: A were-jaguar is not invincible, but is incredibly tough and has a Healing Factor, and the only weapon effective against one is a mystic stone dagger anointed by the jaguar cult. When Ben Daimio finally succumbs to the jaguar spirit inside him, he can't stop it from relentlessly slaughtering everything in its path, but he can't bring himself to kill himself with the blade, and he's too fast and vicious for anyone else to get close enough kill him with it. Eventually, he commits Suicide by Cop by provoking a fight with a Wendigo, another super-strong, bulletproof monster created as a result of a human being cursed by a spirit.
• Last Daughter of Krypton: When Supergirl first fights the Worldkillers, their leader boasts that only a Worldkiller can defeat a Worldkiller. Supergirl exploits this by grabbing one Worldkiller's Combat Tentacles and stabbing another one with them.
  Reign: Only a Worldkiller can defeat another Worldkiller. Why continue a fight you cannot win?
• In Les Légendaires, Anathos reveals in his final stand against the Legendaries that only a God can kill another God. Since he is at this point the only God left on the planet, the only option for them to kill him would be if he committed suicide. They end up defeating him by stabbing him with the sword of his host Danael; since said sword was made from Danael's (and as such Anathos') blood, it's technically part of him.
• Mendy And The Golem: After Mendy is forced to give control of his golem to Ludmila Novakova, a rabbi tells Mendy that nothing can stop a golem. Mendy replies that another golem can.
• The Transformers: Robots in Disguise: The Thirteen Primes held that only a Prime could kill another Prime. Then Galvatron proved decisively that this wasn't the case, by killing Nexus Prime with ease. The remaining Primes fled the planet before he decided to demonstrate that this wasn't a fluke. This, along with pretty much every other part of Cybertronian religion was eventually revealed to be fiction created by a time-travelling Shockwave in order to manipulate the history of the planet in an direction he desired.
• Wonder Woman Vol 1 & Vol 2: This was traditionally the case for gods in the DCU, which was why they were the only entities Wondy didn't worry about using lethal force against; she knew that killing them wouldn't stick and was merely an inconvenience to their current plans. This was of course before before she was turned Darker and Edgier in 2005.

Fan Works

• Abraxas (Hrodvitnon): Colonel Foster thinks that the Heroic Menace vs. Evil Menace form applies when the Many emerge as a threat, surviving Monarch and the Russian military's initial attempt to exterminate them, and the Many are fought by Godzilla and his allies.
• In The Bridge, it takes one Nexus of Magic to have any chance of killing or defeating another one on one. This is because they're simply so much stronger than anything else on either world that the runner-up, Grand King Ghidorah, would be utterly annihilated in a fight with any of them even at only 30-40 percent of their full power. They can technically be defeated, but it would take an entire army of extremely powerful kaiju to have anything resembling a chance of doing so and likely suffer heavy losses in the process. The Guardian Beasts, who if they hadn't been awakened prematurely would be stronger than Godzilla in strength, were created primarily for the purpose of beating one of them when he inevitably escaped his prison and it took the entire Mothra and Battra species to lock him in it in the first time at the cost of their population being reduced to one each. The only being who has ever defeated Grogar, the Nexus of Dark Magic, was Harmony, the Nexus of Light Magic, and even then it was more by cunning and planning than any difference in their power.
• In Imaginary Seas, Poseidon and Demeter are the same class of ship due to their mutual use in terraforming and manufacturing. Because of this, Percy's possession of Poseidon's Authority allows him to unravel Demeter's Authority, nullifying her Klironomia and enabling him to kill those who would otherwise simply heal away their injuries.
• In the J-WITCH Series, it turns out that in addition to his canonical weakness to onions, Tarakudo can only be injured by shadow powers like his own. This gives Jade an advantage over him when she becomes the Guardian of Shadows.
• In A New World, the surviving heroes need to track down Andrew. When they learn that he's in San Diego, Xander quickly concludes that he's going to Comic-Con; and while that can attract a crowd of up to 50,000, he's pretty sure he knows which stands Andrew will head to. As Faith puts it:
  "It took a nerd to catch a nerd."
• Pokémon Wack: Besides Ghost- and Dragon-types (as was the case in canon), Cosmic, Crystal, Wind, Time, Fear, Zombie, Chaos, Divine, Meme, and Heart are all types that are super-effective against their own type.
• In the Pony POV Series, this is the case with the Draconequi, as due to a failsafe only a member of their family is capable of killing their mortal form and it sticking. If anyone else does it, they can Body Surf into another host. As Discord did when Galaxia shattered his statue the first time and later exploited by him to escape the second time. This is a failsafe their parents put in place. No longer the case as the Elders discontinued the rule for the above mentioned stunts by Discord.
• In Tender Words, Chat Noir is badly injured despite his suit when an akuma throws his own staff back at him.

Films — Animated

• In The Incredibles, Syndrome's Omnidroids are so tough that only their own claws can pierce their shell. Mr. Incredible beats the first one by climbing inside so that it attacks itself to get at him. In the climax, Bob realizes that he can use its recently detached claw as a spear to stop the Omnidroid terrorizing their city.

Films — Live-Action

• With no other way to defeat the vampires in 30 Days of Night, Eben becomes a vampire himself and challenges Marlow, who accepts him as the "pack leader" of the humans and the two duke it out one-on-one.
• DC Extended Universe:
  • Man of Steel: No one knows about kryptonite (yet), so the only one who's able to stop the rampaging Kryptonian General Zod is Superman, a Kryptonian himself, being strong enough to break Zod's neck.
  • Wonder Woman: Diana was led to believe that the God-Killer, a legendary weapon forged by Zeus himself to slay other gods (specifically Ares) is a sword, which she steals while fleeing Themyscira to join the war. When she finally confronts Ares in battle, he easily destroys the sword and reveals to her the truth: the only thing in the world that can kill a god is another god. The actual God-Killer is Diana herself, as the daughter of Zeus. And she ends up doing just that.
• In Left for Dead, the only thing that can destroy the demonic ghost Mobius Lockhart are his own weapons: a pair of pistols he claims were forged in hellfire.
• Marvel Cinematic Universe:
  • In Captain America: Civil War, Captain America's indestructible Vibranium shield, which previously blocked a blow from Thor's hammer, is scratched by Black Panther because his claws are also made of Vibranium.
  • In general, the greatest weaknesses of and the only things that can destroy an Infinity Stone are other Infinity Stones and people empowered by an Infinity Stone. In The Avengers (2012), the fact that Loki's scepter can penetrate the Tesseract's shield hints at both their natures as respectively the Mind and Space Stones. Scarlet Witch is highly effective against the same Mind Stone because she received her powers from it to the point that she can destroy it. Thanos uses all six Stones to destroy themselves in Avengers: Endgame, and later in the same film resorts to using the Power Stone to defeat the Space Stone-empowered Captain Marvel.
• In Mega Shark vs. Giant Octopus, the entire U.S. Navy couldn't take down one of these creatures. The plan? Have them kill each other!
• MonsterVerse: The Menace vs. Menace kind, mainly Heroic Menace vs. Evil Menace. Although the government and military would much rather attempt killing the Titans on their terms using manmade weaponry, the reality is that Militaries Are Useless against these gigantic, ancient, borderline-Eldritch Abomination animals; and whether humans admit it or not, humanity is ultimately reliant for survival on the continued existence of Protector Titans such as Godzilla and Kong, who keep the non-Alpha Titans in check via Asskicking Leads to Leadership and who will duel and defeat the more threatening Titans such as Ghidorah and others, with the government's and Apex Cybernetics' attempts to find a way of reaching Godzilla and Kong's power levels always backfiring horribly.
• Ninja 3 The Domination:
  "Only a ninja... can destroy a ninja."
• The whole premise of Pacific Rim: "To fight monsters, we created monsters of our own." Or, in other words, the only thing that can kill a horde of colossal Kaiju (without massive collateral damage) is a legion of equally Humongous Mecha.
• Transformers: Revenge of The Fallen: The Fallen is, as his name implies, a Fallen Prime. It is said that only another Prime can kill him, and naturally Optimus is the only one left. Showing a high level of Genre Savvy, he refuses to engage Optimus and simply stays in his base until Optimus has been killed. Once Optimus gets better (as Optimuses do), the Fallen still avoids getting close to him. He doesn't engage Optimus until his plan has been foiled, by which point he has nothing left.
• In The Wolverine, Wolverine's adamantium claws are severed by a superheated adamantium blade wielded by the silver samurai.

Literature

• In the Arcia Chronicles, the Arc Words in The Prophecy of Eric, "Darkness will protect from darkness; light, from light," foreshadow the protagonists' discovery that the best way to combat dark or light magic is with more dark or light magic, respectively.
• The Dresden Files:
  • Nicodemus Archleone, leader of the Denarians, is protected by the noose that hung Judas, which regenerates damage from any cause... except for itself.
  • In Dead Beat, only someone surrounded by necromantic energies could approach the nexus of the Darkhallow and live. The only way anyone but another necromancer could get near it was to use necromantic energies on something non-human, which technically isn't forbidden. Luckily, Harry just happened to be near a tyrannosaurus skeleton when he found this out...
• In Harry Potter and the Half-Blood Prince there is a inversion. When the new (unnamed) Prime Minister is warned by the new Minister for Magic (Rufus Scrimgeour) that Voldemort is on the move, the PM remarks that the Ministry should be able to handle him since "you can do magic." Scrimgeour reminds him that Voldemort and his people can do magic too. In other words, magic is less effective when used against other magic users.
• In The Hollows by Kim Harrison, law enforcement generally sends the same species as the criminal they're dealing with. They know all the ins and outs of how they work, and can defend themselves against their usual tactics. So vamps are sent after vamps, witches after witches, banshees after banshees, etcetera etcetera. Playing mix and match tends to have... poor consequences.
• Journey to Chaos: Eric's plan at the start of Transcending Limitations is to become a god (partly) to be better able to defend himself from Gruffle, who is now a Grim Reaper.
• Comes up with regard to the unmage in Magic Steps. Because the nature of unmagic is to negate true magic, all the power of the entire mage body of Winding Circle (one of the two great schools of magic in that part of the world) is useless against the unmage. The only thing that can counter unmagic is unmagic, which requires either another unmage (which Winding Circle doesn't have) or Sandry's unique power to "spin magic".
• Percy Jackson and the Olympians: Beings such as gods and monsters can be hindered by mortal means, but not seriously harmed or destroyed. As such, most heroes carry weapons made from divine metals like celestial bronze, which can both kill monsters and prevent casualties by passing through mortals like a ghost. Demigods, being somewhere in between, are vulnerable to both mortal and divine weapons.
• The Raven Tower: Gods can only be killed by an attack from another god or by losing all of their power. Of the known deicides by humans, one used a weapon that had been imbued by the victim god to strike its targets dead, and the other starves the god to death by cutting off the Human Sacrifice it needs to fulfill a Magically-Binding Contract it had entered.
• In the Sword of Truth series, the D'Harans say that they are "the steel against steel so that the Lord Rahl can be the magic against magic." Since only the Lord Rahl has the ability to combat magical threats, everyone else has the duty to combat physical threats (and they tend to get concerned when he tries to deal with them himself).

Live-Action TV

• In Angel season 4, Angelus figures out that the only thing that can harm the Beast is a knife crafted from its own rocky hide. Which it had conveniently crafted already as an offering to its master.
• Buffy the Vampire Slayer: An episode has the gang threatened by the ghosts of native warriors. Buffy notices they can be hurt by their own weapons.
• One of the spells in Charmed for defeating a ghost only works if it's said by another ghost. Fortunately, becoming a ghost doesn't require that you actually die, just be unconscious and near death.
• Delete: Lucifer made a second AI tasked to destroy the first based on this theory. The first easily destroys it.
• In Demons only vampires can kill other vampires. Anyone else first has to shoot them with a high-tech bullet containing their DNA reanimated by electricity, which turns them back into humans.
• In Emerald City, Dorothy has been told that only a witch can kill a witch. So when she runs into the Witch of the East, who immobilizes her with magic and takes her gun, demanding to know how it works, Dorothy tricks her into pointing the gun at her own head and pulling the trigger, thus killing herself.
• In Kamen Rider Zi-O, the villainous Another Riders have Resurrective Immortality and can only be beaten permanently by the powers of the Rider they imitate. Unfortunately, their existence has the side effect of retconning the heroic Riders out of existence; fortunately, Zi-O's whole gimmick is Power Copying. Fellow power-copier Kamen Rider Decade could presumably also do the job, but he spends most of the series pretending to be evil as part of a Stealth Mentor act. In The Movie, Kamen Rider Den-O (who's immune to changes in the timeline) demonstrates that the originals can do it too if they can dodge the retcon; later on in the series, mounting time paradoxes eliminate the retcon element, meaning that more Legend Riders actually get to help him battle their evil doppelgangers. Zi-O also eventually gets around the restriction by using a Mid-Season Upgrade, as it serves as an Immortal Breaker.
• Supernatural:
  • The only sure way to kill angels is with an angel's blade, although humans have occasionally nabbed one of the things. Well, theoretically they could also be killed by asking God for help (not that he's likely to), but that's just cheating. Still, the threat alone is enough to cause a high angel like Zachariah to run for the hills.
  • Archangels take it even further, as they can only be taken down by an archangel's blade. Not only that, but an archangel's blade doesn't work unless it's wielded by another archangel.
  • According to lore, the only way to kill a dragon is with a sword forged with dragon's blood.
    So you need one to kill one, but you got to kill one to make one. How does that work out?
  • The only way to permanently kill Leviathans, aside from a Villain-Beating Artifact that can only be used once, is for them to be eaten by other Leviathans. They can be rendered inert via decapitation, but they only stay dead as long as the severed head is kept separate from the rest of the body. If the head is left close enough to the body, it will reattach and the Leviathan will come back to life.
• One episode of Xena: Warrior Princess dealt with a villain making weapons out of Hephaestus's metal, which can only be damaged by other weapons made of Hephaestus's metal. Including, it turns out, Xena's chakram.

Mythology

• Older Than Feudalism example: In a poem ascribed to Theocritus (3rd century BCE), Hercules discovered that the only thing that could pierce the Nemean Lion's hide was its own claws. Hercules had already strangled it to death by this point — he just wanted to skin it.
• In an undated Greek myth, the twin giants Otus and Ephialtes were so strong they could only be harmed by one another. Artemis tricked them into shooting one another with their spears, killing both brothers simultaneously.
• In Hindu Mythology, it is said that the Brahmastra, the ultimate weapon, can only be overcome by another, stronger Brahmastra.

Other

• In the Evillious Chronicles, a demon contractor can only be killed with the power of another Demon of Sin. This is usually accomplished by using the Vessel of Wrath, which has been changed into various weapons like knives, swords, and even bullets to kill contractors.
• A lot of werewolf and vampire fiction states that one of the few things werewolves and vampires are vulnerable to (except, you know, silver, stakes, and such) are bites and scratches inflicted by another werewolf or vampire.
  • Alucard and Blade are both vampires who hunt vampires.
  • Van Helsing: The only thing that can kill Dracula is a werewolf.
  • In the Old World of Darknessuniverse, werewolf claws do aggravated damage, meaning that they are one of the few ways to easily take down another werewolf or any variety of supernatural beasties.

Tabletop Games

• In BattleTech, mechwarriors often boast that to take down a BattleMech requires another. Other armed forces (combat vehicles, infantry) could conceivably do so, either with rare super-powerful vehicles with BFGs of their own, or lots of casualties, but the BattleMech remains king of the battlefield because of the sheer tenacity (due to compartmentalized construction) and low manpower requirements to deploy (just the pilot).
  • This claim is just as often shown to be bullhonkey, especially by those factions who still embrace 'traditional' combined-arms warfare (Clan Hell Horses in particular). Battlemechs are in many ways treated as heavy cavalry was in the medieval ages: Undoubtedly powerful, but just as much because the way societal factors (a Feudal Future full of low-population-density planets where Urban Warfare is rare, available manpower is restricted, and strategic mobility is king) than due to technological ones.
  • Because of its simplicity and brutality, the Awesome Assault Battlemech quickly gained a reputation for being a very difficult opponent, which led to an in-universe saying: "The only defense against an Awesome, is another Awesome." While this isn't strictly speaking true, its legendary toughness and firepower make it hard to counter directly without employing another Awesome against it.
• In the Chronicles of Darkness, a spirit's natural attacks count as a secondary Bane for any spirit two or more Ranks lower, meaning that powerful spirits can shred their weaker kin with a simple touch.
• In Deadlands, The Dragon to the Reckoners, Stone can only be killed either by shooting him with bullets that should've killed him on Gettysburg, some of which are in his guts or by any weapon shot by his own hands.
• In Dungeons & Dragons 3rd edition and 3.5, creatures with damage resistance that can only be pierced by magical weapons have their natural weapons (if existing) able to pierce that same resistance, so every creature is capable of killing its own species. Though this doesn't apply if the damage resistance is to something else, like a specific metal type (such as silver) or alignment: the claw and bite attacks of a dragon with damage reduction that can only be overcome with magical weapons, but a werewolf's own claws and teeth don't count as being silver.
  • In 1st Edition, before serious attempts were made to balance it with other game elements, psionics was something that non-psionic opponents had little or no defense against. You pretty much had to use psionic monsters and enemies to keep a psionically-gifted PC from running roughshod over a campaign.
  • In certain fluff material, it's mentioned that some of the most famous dragonslayers were benevolent metallic dragons either in mortal disguise or not who hunted the more wicked chromatic dragons.
• Leviathan: The Tempest: Due to their Lovecraftian nature, Leviathans normally enjoy exceptionally potent defenses against magic that would influence their thoughts, emotions, or souls. However, these defenses have one chink: They don't apply if the Leviathan is trying to alter or manipulate its own mind. Quite aside from clones and alternate-universe versions of a Leviathan (both of which are entirely possible given the kinds of powers Leviathans have), a Leviathan's Beloved and Ahabs are both metaphysically extensions of the Leviathan and thus capable of exploiting this loophole.
• Shadowrun uses this heavily. All scenarios take part on three planes — the physical plane ('our' reality), the astral/magical plane (accessible to mages), and on the Matrix (accessible to deckers and technomancers). The three planes commonly interact, and when they do having monopoly on power in one of those planes gives you considerable power to influence the outcome of the scenario (though usually it's 'won' in the physical one), and thus all shadowrunning teams — as well as whoever you're hired to run against — should be expected to project power in all three planes. The most common example is Summon Magic, which hires spirits from the astral plane to manifest into the physical world, where they're powerful entities that are nigh-Immune to Bullets. If your team has no mage or phys adept to banish or magically beat them into submission, your sammie isn't going to cut it against them. Similarly, if an opposing decker gets ahold of traffic control for your self-driving car via the Matrix, that car isn't going to help you chase down that escaping enemy any time soon.
• Averted for the most part in Warhammer 40,000, where just about every superweapon can (eventually) be countered by sufficient application of More Dakka. Of course, if you didn't prepare for one, you're screwed.
  Despise infantry if you must. Crush them underfoot, by all means. But do not ignore them. Battlefields are littered with the wreckage of Titans whose crews ignored infantry.
  • The Tau were on the receiving end of this against Imperial Titans, being Combat Pragmatists who don't see the point of pouring billions in a single giant warchine when hundreds of Boring, but Practical troops could be produced instead (the closest they have to a Titan in terms of size and power is a spaceship). Then they designed a bomber specifically designed for killing huge targets, which not only killed the Titan in seconds, the other three Titans retreated before it could destroy them as well.
  • Warhammer tropes really should indicate when they were the case since the game zig-zags many tropes with each edition. Before 8th edition, tanks and similar vehicles were invulnerable to most infantry weapons and generally had to be engaged with anti-vehicle weapons. The rules in most editions also forbade most units from splitting their fire; either the anti-tank squaddie wasted his big gun on the same infantry his unit shot at, or the riflemen wasted their shots on the tank so the anti-tank trooper could target it. As of eighth edition, every attack has some minimal chance to inflict Scratch Damage against any target, and splitting fire has become easier.
• In Werewolf: The Apocalypse, one of the setting ending scenarios has the Wyrm having become so powerful that only its own weapons can even hurt it.

Video Games

• "???"-type enemies in Alter A.I.L.A. Genesis are the enemies who use Psych-elemental attacks the most often, but they are also the only enemy weak to it.
  • Many other enemies do this too; robots use Shock attacks the most, and humanoids tend to use Force, both of which are the elements they're most weak to.
• Arknights:
  • When war broke out between the nation of Aegir and the rapidly-evolving Seaborn, the Aegirians opted to combat the Seaborn with Abyssal Hunters: melee-wielding super soldiers infused with Seaborn blood. Skadi finds out the truth the hard way in "Under Tides".
  • The Emperor's Blades of Ursus have fragments of a demonic entity known as Collapsal sealed into their bodies using specialized containment suits, and they serve as part of Ursus' defenses against the Collapsals encroaching in the north. Similarly, operator Typhon fights the Collapsals using a great bow with fragments of a Collapsal sealed in it using esoteric Sarkaz Originium Arts.
• In Breath of Fire: Dragon Quarter, dragons can only be harmed by other dragons. This means that if Ryu transforms in a conventional battle (including the vast majority of boss battles), he is invincible. There is one exception: A certain enemy dragon can be harmed with conventional weapons if a transformed Ryu attacks first and "breaks the defense".
• In Castlevania: Order of Ecclesia, the Dominus glyphs, which are required to kill Dracula in this particular game, are made from Dracula's own power.
• Magus in Chrono Trigger, a Barrier Change Boss, can only be damaged by the element he's currently using.
• Downplayed in that a Custom Robo commander can technically be defeated by relentless carpet bombing, but as robos become cheaper and more widely available robo commanders become the only economical means of combating other robo commanders, especially in densely populated areas. Then came, Rahu, which can only be beaten by robo commanders and is only beatable at all because, for reasons no one can explain, the world-destroying menace decided to start using a robo. A toy robo rather than, say, a military-grade one.
• Destiny: Downplayed. Paracausal entities defy the laws of physics by definition, making them extremely difficult to kill by conventional means — it can be done, but generally requires More Dakka and There Is No Kill Like Overkill. Therefore, the most reliable way to kill a paracausal being is with another paracausal being, who can throw punches in the same metaphysical weight class. This is how Guardians are able to kill Eldritch Abominations and Physical Gods despite being a bunch of self-trained Mildly Military irregulars, and likewise how they tend to die in droves against the same despite their powers making them one man armies. It's either that or somehow separate them from their paracausality, turning them into regular flesh and blood.
  • In Destiny 2: Season of the Witch, in order to combat Xivu Arath on an even playing field— since fighting Xivu only makes her stronger— this becomes the crux of the season's plan. Eris Morn enacts a ritual to become a nascent Hive God herself, hijacking the Hive tribute structure to empower herself to challenge Xivu.
• In The Elder Scrolls series, dragons are ageless beings with divine souls, akin to highly destructive angels. While anyone of sufficient ability can slay the physical form of a dragon, permanently killing one requires absorbing its soul, something only beings who also have dragon souls can do. In order to serve as a natural predator to the functionally immortal dragons, Akatosh, the draconic God of Time and chief deity of the Nine Divines Pantheon, created the Dragonborn, rare mortals gifted with the immortal souls of dragons. Naturally, dragons see these "Dovahkiin" as Humanoid Abominations for what they are capable of. The Player Character of Skyrim is the so-called "Last Dragonborn", sent to oppose the return of Alduin the World Eater, the "first born" of the dragons.
• The Foreigner class of Fate/Grand Order is super effective against Berserkers and resists them, and the only way to deal double damage to them is to either use an Alter Ego or another Foreigner.
• Final Fantasy Tactics:
  • The "Faith" stat dictates not only a mage's attack power but how much damage they incur from enemy spells as well. A character with very low Faith is thus virtually immune to magic, while a character with high Faith is very vulnerable.
  • Low Faith isn't quite as good as it sounds, because it makes the character virtually immune to all magic, including healing spells. So a character can be impervious to magic, but only at the price of having to rely entirely on items for healing. Though it's actually not a bad trade-off in this game.
• In Fire Emblem: Awakening the last act of the game is spent finding a way to stop Grima, the Big Bad of the game. Your party goes to a shrine to Naga in order to perform an awakening ceremony to hopefully give the Falchion the power to slay Grima. However, Naga reveals after the ceremony that slaying Grima with the Exalted Falchion will only put him into a 1000-year sleep, and only his own power is strong enough to truly slay him. This causes the Avatar to realize that since they were supposed to be the Fell Dragon's vessel, they can also tap into his power, and thus permanently kill him, at the cost of their life.
• Used to justify being able to play the titular kaiju in the single-player campaign of Giants: Citizen Kabuto: After inadvertently freeing Kabuto to rampage over the Shattered World whilst defeating her mother at the end of her campaign, Delphi the Sea Reaper sorceress uses a shard of the magical Kabuto Stone to transform into a copy of Kabuto, in hopes of this making her strong enough to defeat it. Played with, in that whilst Delphi does eventually throw down with Kabuto in her transformed body, she only knocks it out briefly and is then defeated when it wakes up, forcing Baz the Mecc to kill Kabuto by shooting it in its groin-mounted weak spot.
• God Eater: The Aragami are nigh unstoppable monsters made from Oracle Cells that can devour anything in their path. To fight them, humanity resorted to infusing people with Oracle Cells to make them part Aragami and armed them with weapons made of Oracle Cells that essentially eat the Aragami.
• Iji was enhanced with nanomachines in order to combat the threat of alien invaders, because nanoweapons are about the only way to even scratch the alien's armor, much less go up against one and win.
  • And the final boss, while not outright immune to heavy weaponry, is best taken down with his own projectiles, which inflict the most damage on him.
• The Dragon Element in the Monster Hunter games is the best one against Elder Dragons and the vast majority of weapons carrying Dragon Element are made from Elder Dragons to begin with. Further, the Dragon Element is stated by the devs to deal damage by attacking the mind. Elder Dragons are by far the most intelligent of monsters, and thus the most vulnerable.
• In Paper Mario: The Thousand-Year Door, during the Inevitable Tournament, one of your enemies is a pair of metallic, spike-covered critters... you can't hurt them with jumping-attacks, hammers, fireballs, or anything else. In fact, it's a Hopeless Boss Fight... until Yoshi Jr. joins you for the rematch. By eating one and spitting it at the other, he's capable of damaging them - because, as it turns out, their only vulnerability is themselves.
• In Persona 3 and Persona 4, Personas are actually Shadows tamed and controlled by a sentient being's ego (with Shadows themselves being the coalesced feelings of despair and loathing in all people, so it can be said that Shadows are the Persona of humanity). As such, they can (and have) turn back on whomever they're a Shadow of and consume them, but are also the most effective way to fight Shadows.
• Pokémon:
  • A few types are weak to themselves:
    • The Dragon-type is super effective against only one type: itself. Nevermind its Ice-type and Fairy-type weaknesses, sometimes pitting another Dragon-type is your best bet due to their sheer strength.
    • Similarly, the Ghost-type also has a weakness to itself, even though it's also vulnerable to Dark-type. Since Giratina and the Dreepy are both Ghost- and Dragon-type, they are often the best counter to themselves.
    • Hoopa Confined, Lunala, Dusk Wings Necrozma, and Shadow Rider Calyrex are all dual-type Psychic/Ghost, so they have the dubious honor of having the only type combination with a double weakness to one of their own types! ^*Had a Pokémon with this type combination existed in the first generation, it would've truly had no weaknesses—it was immune to Ghost, Bug-type moves did neutral damage, and Dark didn't exist. Not like those first two mattered, what with said moves being horribly underpowered.
    • The Stellar type is technically weak to itself, due to Stellar-type moves being super effective against Terastalized Pokémon and the Stellar type only being available via Terastalization.
  • In Pokémon Red and Blue, the Psychic type, while resistant to itself on the Elemental Rock-Paper-Scissors tree, was such a Game-Breaker that the only reliable counter was another Psychic. This was severely nerfed for Pokémon Gold and Silver onwards, where the new Steel and Dark types (respectively) resisted and No Selled Psychic attacks.
  • When you start messing around with the Elemental Rock-Paper-Scissors, you may start getting combinations of types that wouldn't normally resist themselves paired with a type that is weak to said type—like how the Fighting/Steel Lucario is weak to Fighting, the Bug/Grass Parasect is weak to Bug, and the Steel/Ground Steelix is weak against Ground. ^note These types are: Ground, Fighting, Flying, Rock, Fairy, and Bug. No, Normal doesn't count.
  • In the Pokémon XD spin-off, Shadow attacks are universally super-effective against everything... except another Shadow Pokemon. Keeping one or two Shadow Pokemon on your team that happen to know some ordinary moves is therefore a good strategy (at least for a while, since Shadow Pokemon cannot level up).
  • Types that usually resist themselves ^note Fire, Water, Grass, Electric, Ice, Poison, Psychic, Dark, and Steel get a taste of this in the Inverse Battles introduced in Generation 6. Ice especially as it has no other resistances in normal gameplay, so a pure Ice type in an Inverse Battle would only take super effective damage from Ice attacks.
• R-Type: The series indicates that the only weapon that is truly effective against the Bydo is the Force Device, a semi-controllable pod that can be attached to either the front or back of the player's ship. The big secret of the Force Device's construction is that it contains an embryonic Bydo lifeform as its core, and the source of its power. Thus, only the Bydo can truly harm the Bydo.
• In RuneScape there are two ways to definitely kill a god: using an Elder Artefact from The Old Gods, or a Wave-Motion Gun fueled by divine energy.
• The Mortal Blade in Sekiro: Shadows Die Twice can kill immortal creatures, but drawing it from its sheath kills you on the spot. As such, only an immortal can actually use the thing; fortunately, Sekiro qualifies.
• Sonic 3 & Knuckles: The first form of the last boss must be damaged with its own missiles. Despite the fact that you are invincible, ramming the boss not only does no damage but wastes the precious little seconds you have.
• StarCraft:
  • This is how the Cerebrates are defeated in StarCraft, with Dark Templars wielding Void energies similar to the Overmind's own.
  For the Dark Templar use energies that are much like my own, and it is by these energies that they have caused me harm.
  • StarCraft II: Legacy of the Void reveals that only a Xel'naga can defeat Amon permanently in the Void. Ouros, being the last Xel'naga not siding with Amon, got around this by giving his essence to Kerrigan and turned her into a Xel'naga.
• In Tokyo Mirage Sessions ♯FE, Mirages can only be defeated by the power of another Mirage. Fortunately, some of the Mirages are willing to lend their power to humans, making them Mirage Masters.
• In Touhou Puppet Dance Performance the titular puppets can only be harmed by other puppets.
• Implied in TRON 2.0. In that universe, human "Users" digitized and sent to Cyberspace are almost Physical Gods. With one corrupted User unleashing a Zombie Apocalypse over multiple computer networks, and the people behind him about to upload an army of mercenaries to conquer the computer world so they control the human one, Ma3a resorts to this logic and uploads the protagonist in desperation.
• In Valkyria Chronicles, Selvaria Bles is a Valkyria whose powers make her a seemingly unstoppable warrior who singlehandedly turns the tide of battles. The only person who manages to defeat her with her Valkyria powers active is Alicia, who is also a Valkyria. Selvaria does, however, turn off her Valkyria powers later to fight fairly.
• Warcraft III:
  • The Siege Engine is basically a steam-powered battering ram: it deals high damage to buildings, can't attack ground units, and has building-type armor... which is particularly weak to siege-type damage, which all factions' artillery have. Downplayed, in that killing it with normal units is only a bit longer.
  • Ethereal units are a subversion: they can cast spells but can't attack and can only be harmed by magic, but two ethereal units can't attack each other. Two ethereal units can kill each other if they both have offensive spells, however.
• The Witcher 3: Wild Hunt: Unless a Higher Vampire is finished off by another Higher Vampire, it will regenerate any injury. However, that regeneration can take decades or centuries in case of serious damage, so humans can still defeat Higher Vampires.
• This is a recurring concept in the Xenoblade Chronicles games:
  • The Mechon of Xenoblade Chronicles 1 are all but immune to conventional weapons. However, weapons crafted from trashed Mechon parts can cut through their armor just fine.
  • In Xenoblade Chronicles 2, Pyra/Mythra were originally awakened to stop Malos’s campaign of mass destruction. All of them are referred to as Aegis and all had the same point of origin.
  • In Xenoblade Chronicles 3, Noah’s hidden sword, the Lucky Seven, is made from the same material as the flame clocks, making it one of the only weapons that can destroy them. And pretty much anything else in Aionios as well, as its Origin Metal is responsible for the world’s current stats.
  • Expanding on a previous example, Xenoblade Chronicles 3: Future Redeemed, implies that Matthew’s gauntlets and N’s sword contain Pyra/Mythra/Pneuma and Malos/Logos’s Trinity Processor core crystals, making them necessary to kill the now destructive third core, Alpha/Ontos.

Visual Novels

• Played With in Dies Irae. While killing an Ewigkeit user is doable in theory for a normal human, in actual practice it is nigh impossible. This is due to the way Die Ewigkeit works as it gives its users effectively extra lives on top of a whole host of other abilities. Thus the only really effective way to kill one is to use weapons that take "several lives on each use", and normally such weapons like bombs and nukes just aren't practical. Hence why Ahnenerbe exists, weapons wielded by Ewigkeit users, as they attack the soul directly and can take all those extra lives with more limited attacks. The only known instance of a normal human killing an Ewigkeit user was Shirou killing Wilhelm at the end of Kasumi's route, and that relied on a very specific loophole created by the user's own powers.
• Played With in Fate/stay night and related works. Servants are said to only be vulnerable to other Servants, but while they are immune to conventional methods of attack (including military hardware up to and including nuclear bombs), in reality, any ability infused with magical energy should be able to harm them. In practice, however, Servants are so superhuman that there are extremely few modern magi capable of actually landing a hit on them, meaning that the only way to reliably harm a Servant is through another Servant. Rin claims that even a paper knife can harm one, but only as long as it's wielded by a Servant and infused with mana. That being said, it's entirely possible for a magus to harm a Servant under the right conditions; Rin was able to claim one of Berserker's twelve lives by catching him off-guard with her magical jewels, and Shirou's copies of legendary weapons allow him to fight Servants for a limited time and even defeat them.

Webcomics

• Alice Grove: The ancient Super Soldiers are so durable that even an orbital bombardment from contemporary technology couldn't scratch them; only their own Super-Strength can hurt them. Even then, for Sedna to kill Church, she has to tear her own arm off and use the jagged bone as a shiv.
• The titular Mons of Battle Kreaturez are protected by invisible ReinforceFields that spike in response to duress, making them Nigh-Invulnerable. Compounding this, they also have a Healing Factor that allows them to recover from most injuries. This means a rampaging Kreature can only reliably be stopped by another Kreature, necessitating the art of Kreature Taming.
• In Homestuck, it's believed that the only reliable way to kill a nigh-invulnerable First Guardian (or a creature possessing its powers) is to send another to fight it. This isn't precisely true; it's just that the First Guardians possess so much raw power that they're in their own tier, and very little even comes close. It is suggested, for instance, that God-Tiered Vriska at her full strength, making full use of her luck-manipulation powers, and cheating her ass off (as she usually does) would have a chance at defeating one... if a slim chance.
• The Last Halloween: A fundamental rule of immortality — "immortals can kill other immortals" — is revealed when Ba'al crushes Robert to death.
• An interesting example in Tower of God with Arie swordsmanship. Known to be uniquely powerful and impossible to describe, Word of God even stated that the only way to defeat a user of Arie swordsmanship is to either be overwhelmingly stronger than them or to be better at Arie swordsmanship than them.

Web Videos

• False Swipe Gaming: Downplayed with Snorlax in Gen 2. While anyone can technically defeat Snorlax, the only way to knock out Snorlax in one hit without a Critical Hit is for another Snorlax to use Self-Destruct.

Western Animation

• Chaotic: Creatures from the spirit lands who are in their spirit form cannot be harmed by anything except for other creatures in spirit form. The downside is that creatures from the spirit lands can only exist outside of the spirit lands for a limited time unless they take on a physical form.
• Courage the Cowardly Dog had the Kangaroo Monster, a creature so badass the only thing that could harm it... was another Kangaroo Monster! When Eustace was turned into one of these creatures due to a bone transplant and goes on a globe-trotting rampage with a kidnapped Muriel, Courage goes through the same surgical procedure to become another giant kangaroo and fight Eustace.
• Dexter's Laboratory:
  • In "Rushmore Rumble", Dexter uses a giant stone Abraham Lincoln (who shoots missiles out of his hat!) to fight Mandark's giant stone George Washington. However, the trope is subverted when the two stone presidents find out they are honest men who have a lot in common, stop fighting, and walk off as friends.
  • In "Monstory" Dexter gives Dee Dee what he thinks is a silencing potion, but instead mutates her into a monster. The only way to get her to shut up? To become a giant monster himself and have a knock-down, drag-out kaiju battle!
  • "The Laughing" features a variant. Dexter becomes a mischief-making were-clown, and Dee Dee subdues him by learning the art of mime.
• Final Space: Implied in "The First Times They Met" with the evil KVNs. They are stated to be nearly indestructible, which is demonstrated throughout the episode, but towards the end, the main KVN easily kills the last one himself by punching right through him and tearing out a vital heart-like component.
• Parodied in a "What If" episode of Futurama, where the Planet Express crew creates a Giant Zoidberg as only an "even equally big" monster could defeat a tall monster rampaging through the city. This fails miserably as Giant Zoidberg immediately goes on a power trip and rampages through the city, and so the two giants fight and kill each other in the ensuing turf war.
  • In the second movie, The Beast With A Billion Backs, electromatter can only be damaged by other electromatter.
• Gerry Anderson's New Captain Scarlet introduced a Russian super-tank the size of a small apartment building called a Druzhnik, which was set up as being pretty much entirely untouchable by conventional weapons; a GDI Mammoth Tank might've had a chance in a 1v1 but the heaviest weapons SPECTRUM had access to just bounced off it. The third time the Mysterons managed to swipe one, in the grand Gerry Anderson tradition of Prop Recycling, Scarlet pretty much quoted the trope word for word:
  "Nothing can touch a Druzhnik, except for another Druzhnik!"
  • He then proceeded to prove his point, having borrowed one from the Russians. It was rather badass.
• Jackie Chan Adventures: "Magic must defeat magic!" Magic Versus Science plays something of a role in the series where Magic A Is Magic A, but the main problem is that trying to use Science B in the equation produces either null results or Unpredictable Results.
  • The above quote is said by Uncle, a skilled wizard and magic expert, usually to the government agent Captain Black, to explain that magical problems require magical solutions (like fighting the demonic dragon Shendu), though Black doesn't usually take the hint.
  • The biggest example is when Jackie uses a laser cannon to destroy the Chinese zodiac themed Talismans in an effort for No Macguffin No Winner. While the physical Talismans were destroyed, the magic within them each transferred to a corresponding animal, forcing them to search for the Talisman powers again in a different form.
  • Played with in the series finale, to fight an empowered Drago, Uncle and Tohru summon Drago's father Shendu to fight him ("Demon must defeat demon"). This is, however, a stalling technique so Uncle could banish both of them to the Netherworld.
• My Little Pony: Friendship Is Magic: In "To Change a Changeling", Pharynx uses the Stop Hitting Yourself approach to defeat the Maulwurf.
• The Pirates of Dark Water: In one episode, Ioz is captured by Ghost Pirates. Tula and Ren try to rescue him, but any attack they try just passes through the pirates and Ioz's chains, while the pirates can hurt them. Tula comes up with a way to temporarily turn Ren into a ghost so that he can fight back and save Ioz.
• On South Park the only way to defeat a giant stone Abraham Lincoln is with a giant stone John Wilkes Booth.
  • Also, immortal beings like Cthulhu can only be killed by other immortals.
• In the ThunderCats (1985) episode "The Ghost Warrior", the ghost of the evil warlord Grune the Destroyer awakens from his ancient slumber and goes on a rampage. The ThunderCats try to fight him, but nothing they try can hurt him, while he can hurt them. Eventually, Lion-O realizes, "We fight a ghost... with another ghost!" and summons the ghost of his mentor Jaga, who defeats Grune and banishes him back to the afterlife.
• Ultimate Avengers provides a technological example: vibranium armor can only be penetrated by vibranium weapons^note this is implied to be the case in the rest of Marvel's works, but this is the only work that outright states it.
  • Nuclear warheads and the Hulk also work, but those tend to be more trouble than they're worth.

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