"Magic must defeat magic!"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 on 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.
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Anime and Manga
- In Neon Genesis Evangelion, the Evas (who are pretty much Angels anyway) are usually the only things on Earth which 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.
- 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 which could have legitimately beaten a Megadeus.
- Ryo Takatsuki's nanite-powered Super-Powered Evil Side in Project ARMS has a unique power to negate the Healing Factor of other ARMS.
- Blood: The Last Vampire has this as its basic premise.
- 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 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.
- In Baccano!!, the only way an immortal can die is to be absorbed by another immortal.
- 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 an 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".
- In 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.
- 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.
- 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.
- 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 a 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 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 JoJo's Bizarre Adventure, a Stand (an invisible telekinetic construct) can only be harmed (inflicting sympathetic damage on its creator) by another Stand. Although some Stands can't be harmed at all. However, a Stand User is just as vulnerable to being killed by mundane means as anyone else (which of course, will usually destroy the Stand).
- Zig-zagged in the Gundam franchise: Sometimes Gundams can only be defeated by Gundams, while other times any sufficiently advanced mobile suit can potentially defeat one.
- 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 (like those wielded by Gundams; otherwise beam weapons are ship-mounted weapons that are too large for a mobile suit to carry and can't be aimed fast enough to be effective against agile mobile suits) can hurt them. 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.
- 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.
- 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.
- 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.
- Radioactive material from his natural environment no less.
- When the New 52 version of Supergirl first fights the Worldkillers, one of them 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.
- 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.
- 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.
- 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.
- 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 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 for 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.
Film — Animated
Film — 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.
- 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 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!
- Ninja 3: The Domination
"Only a ninja... can destroy a ninja."
- In The Wolverine, Wolverine's adamantium claws are severed by a superheated adamantium blade wielded by the silver samurai.
- DC Extended Universe:
- Man of Steel: No one knows about kryptonite yet, 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 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.
- 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.
- 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).
- 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.
- 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.
- 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.
So you need one to kill one, but you got to kill one to make one. How does that work out?
- 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.
- 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 killed 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.
- 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.
- 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.
- In Dungeons & Dragons 3rd edition and 3.5, creatures with damage resistance have their natural weapons (if existing) able to pierce that same resistance, so every creature is capable of killing its own species.
- 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.
- 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.
- 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.
- 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.
- 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 BF Gs of their own, or lots of casualties, but the BattleMech remains king of the battlefeild because of the sheer tenacity (due to compartmentalized construction) and low manpower requirements to deploy (just the pilot).
- 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".
- Magus in Chrono Trigger, a Barrier Change Boss, can only be damaged by the element he's currently using.
- 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.
- 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.
- 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.
- The Dragon type is super effective against only one type — itself. note
- The Ghost type also has a weakness to itself, though it's vulnerable to a number of other types as well. Since Giratina is both Ghost- and Dragon-type, it is often the best counter to itself.
- Hoopa Confined and Lunala are both 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! *
- 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
- 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 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.
- "???"-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.
- 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 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 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.
- This is how the Cerebrates are defeated in StarCraft. "For the Dark Templar use energies that are much like my own, and it is by these energies that they have caused me harm."
- Similar to Pokémon, the Dragon element in the Monster Hunter games is the best one against Wyverns.
- The Siege Engine in Warcraft III 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.
- 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.
- 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 PhysicalGods. 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 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.
- The Mechon of Xenoblade Chronicles are all but immune to conventional weapons. However, weapons crafted from trashed Mechon parts can cut through their armor just fine.
- 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.
- 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.
- 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.
- 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.
- 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 weaponsnote .
- 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.
- British forces in the Battle of the Atlantic were commanded by a submariner.
- Frequently inverted by the actual real life military.
- Often, the best way to kill or disable a hostile unit is using something completely different against it; for example, battleships fell out of favor after WW2 because too many of them had been destroyed by aircraft, and a tank's worst enemy isn't necessarily always another tank. This is often because the best use of tanks is in destroying supply lines, rather than because tanks are not effective against other tanks.
- Averted with submarines, Hot Sub-on-Sub Action notwithstanding. WW2 and earlier subs, largely blind underwater and equipped mainly with unguided torpedoes, were basically incapable of attacking each other at all unless the target happened to be on the surface (in which case it would have been just as vulnerable to gunfire and aircraft), and while more modern ones are equipped with weapons that can seek out and destroy another submarine those weapons can often be just as easily be mounted on other platforms (such as helicopters, against which a submerged sub under attack cannot even return fire).
- Diamonds can only be scratched by other diamonds.... Or even harder substances. The first of which, cubic boron nitride, was synthesized in 1957.
- Averted with scorpion venom. Scorpions are immune to the venom of their own species.
- On that note, antivenom in general. Created from the very venom it's used to treat.