History Main / TakesOneToKillOne

** 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 [[QuadDamage double weakness]] to one of ''their own types''! [[labelnote:*]]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.[[/labelnote]]

* ''VideoGame/{{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 [[spoiler:infused with Seaborn blood]]. Skadi finds out the truth the hard way in "Under Tides".

* This is how the Cerebrates are defeated in ''VideoGame/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."

* The Imperial Weapons from ''Manga/AkameGaKill'' 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.

** The above [[CatchPhrase quote]] is said by Uncle, a skilled wizard and magic expert, usually to the [[TheMenInBlack government agent]] Captain Black, to explain that magical problems require magical solutions (like fighting the demonic dragon [[BigBad Shendu]]), though [[WrongGenreSavvy Black doesn't usually take the hint]].

* In ''Anime/TheBigO'', one of the few things that can damage a [[GiantMecha Megadeus]] is another [[GiantMecha 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.

* ''ComicBook/TheTransformersRobotsInDisguise:'' 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.

SubTrope of MutualDisadvantage. SuperTrope to MagicMustDefeatMagic. The opposite of TacticalRockPaperScissors where each type of combatant has some other capable of [[CurbStompBattle curb stomping]] it. However, this can be a subtrope of ElementalRockPaperScissors if an element happens to be weak against itself. Compare BeatThemAtTheirOwnGame, HoistByHisOwnPetard, and SummonBiggerFish. Contrast LikeCannotCutLike and CounterpartArtifacts. See also SerialKillerKiller, which usually doesn't involve the supernatural.