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Curious tendency observed in Elemental Rock-Paper-Scissors universes, where one element will beat another. (Water beats Fire, Fire beats Ice, etc.) These universes often have someone who will completely devote themselves to a particular element. Sometimes they will have entire cultures with that devotion.
...what that means is that they have some very obvious weaknesses. Curiously, usually only the heroes get the idea of diversifying their elements. Either that, or the one-element specialists are fully aware of their situation and develop various tricks and techniques that allow them to defend, to varying degrees, against those elements which counter theirs - so that Scissors Cuts Rock. In some settings, this could even be seen as a kind of Min-Maxing - specializing in one element to the point where you can just brute-force your way past a more generalist opponent, at the potential cost of losing hard to other specialists who counter your element.
Interestingly in actual rock-scissors-paper, throwing the same hand every time is a valid tactic against an inexpert opponent. Basically nobody expects a player to play the same hand twice or more. There are even names for the tactic, among those who care about such things. Also, rock is statistically the most used play, particularly among male beginners.
Compare Crippling Overspecialization and When All You Have Is a Hammer.
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Anime and Manga
With a very few exceptions (the most important characters), everyone in Yu-Gi-Oh! uses a themed deck: fairy tale monsters, insects, robots, penguins, fairies, cartoons, in spite of the fact that these themed decks always prove useless against a deck with the appropriately dominating theme, and many of these themes are pretty much worthless. To be fair, the game itself is designed such that it's difficult for an unthemed deck to provide a full hand of usable cards at any given time.
Played VERY straight in the battle between Pegasus and Kaiba in Duelist Kingdom. Pegasus took advantage of the fact that Kaiba was famous for his Blue Eyes by using dragon capture jar and Dragon Piper. The second is that he also knew that Kaiba's entire deck is built with overly powerful monsters so his reversal of the Crush card virus essentially blasted Kaiba's entire strategy to pieces.
Happens again in Yu-Gi-Oh! The Movie: Pyramid of Light, but this time it's Kaiba who beats Pegasus with this trope in mind. Having learned Pegasus still relies heavily on his toons, he also took advantage of how Toon-type monsters require Toon World to be active on the field. In quickly aiming to destroy Toon World, he tore apart Pegasus's strategy in a matter of turns.
Also, unlike Pokémon, there are no built-in weaknesses to certain types. A card with a fire attribute isn't automatically weak to one with a water attribute, for example.
The anime and manga are spectacularly inconsistent about this. The Duel Kingdom arc in particular runs on the Rule of Cool and Rule of Drama: theme decks are often bizarrely overpowered and elemental weaknesses and consistencies pop up and disappear from moment to moment. This is because the manga was produced before Defictionalisation turned Duel Monsters into an actual card game that required actual rules, and the anime was based on the manga. By the time the Battle City arc was published, the game had become widespread and "expert rules" (a halfway compromise between the actual game rules and the Rule of Cool loose interpretation used before) were introduced to the story. The video games, however, take monster attributes and make them into a several-network game of Elemental Rock-Paper-Scissors.
One of Rurouni Kenshin's Big Bads uses this to his advantage. Once Shishio is hit with an attack, he knows how to perfectly counter it. While Kenshin has a variety of different sword techniques to compensate for this, it sucks for Saito Hajime since all of his special moves are variants of the same basic attack. And when he attacked Shishio with it, he hit the only armored part, negating the attack.
Deconstructed to hell and back (and back to Hell again) in Kaiji, where the first arc revolves around the titular character's ability to manipulate a high-stakes game of rock-paper-scissors (a variant that uses one-use playing cards to represent each hand sign). He ends up buying 30 rock cards in order to beat other players who have scissors. Then, another player named Kitami buys dozens of paper cards in response. After a fierce battle, Kaiji takes Kitami's cards and totals about 30 rocks and 30 papers. Later still, he is forced to re-shuffle his entire deck with the rest of the players... and in the end, his cards end up not being relevant to his final strategy.
In the billiards (you know, pool) manga Breakshot, practically every opposing player has one major strength and sticks to it 90% of the time. Jimmy and Oki's masse shots, Aono's center shots, Ryoji's shotgun shot (which, as it happens, is actually prety unpredictable in its effect, but he's still guaranteed to use it), Jeffrey's miracle shot, and main character Chinmi himself is inordinately fond of jump shots.
Hell, eventually, Chinmi is goaded into relying much much more on jump shots by his mentor to increase his level of skill by mastering the secret jump technique perfected by Douglas Mood, who won 60 straight games using only jump shots.
Eyeshield 21 plays this straight most of the time; Most opposing teams have one or two defining strengths and rely almost entirely on them. The Sphinx' Pyramid Line, the Poseidons' height advantage, the Aliens' Shuttle Pass, etc. In many cases, however, these strengths are so formidable that they can usually win anyway.
Its also not played as straight as it could be, as though most teams had their aces into a specialization, they generally had a pretty effective general team to back it up (Hakkashuko, Shinryujii, Amino, Aliens) or had their specialization be so broad it didn't much matter they were specialized (White knights focusing on defence, 1/2 the game or Sebiuu/Daimon's focus on Offence, the other half). Only the Bando Spiders really played it straight, and even then they had more than just their kicks, and the reason for being so specialized was highly justified.
Hiromu Nishiki in the soccer manga Meister. On a team notorious for players with one spectacular talent and not much else, from Ryuho's expert dribbling to Koori's defensive power, Nishiki stands out. Once a rising star in the youth soccer world, he fell into obscurity after he adamantly refused to play defense in any way shape or form; the way he sees it, he's a natural born striker, and strikers just don't defend. Ever.
In Love Hina, Naru always picks scissors in games of Rock-Paper-Scissors.
In Hunter × Hunter, Gon's special attack is explicitly based on Rock-Paper-Scissors, with his "Rock" attack being by far his strongest, and the only one capable of ending fights against stronger enemies. And stronger enemies will catch on to that pretty fast. Winning when your opponent knows you have to throw Rock to win? That takes talent.
In Naruto, Deidara's sole means of attack are Earth element clay birds. He picks a fight with Sasuke, whose primary attack this point is the Lightning element Chidori and variants thereof. As Deidara loses in Elemental Rock-Paper-Scissors, this ends badly for him.
The magic users of Eric Nylund's A Pawn's Dream all specialize in an elemental pair (the main character is a Life/Death magician, for example). They can use other elements, but they're not as proficient. (However while all specialise, there is no Elemental Rock-Paper-Scissors in play, so this is not in fact a significant weakness.)
In Skulduggery Pleasant by Derek Landy, one of the villain's Mooks has made himself magically immune to fire. The result is that he's very vulnerable to water, with Squick-y results.
In Gone, Sam does paper and loses, so he has to be the first to go into the nuclear plant.
Quinn: Dude. Paper? Come on. Everyone knows you go with scissors on the first round.
In The Dresden Files, a common weakness of more ancient beings is that while they're vastly more powerful than Harry, they're also very set in their ways and inflexible when it comes to combat strategy. When Harry duels Arianna Ortega in Changes, after successfully fending off her first attack he's surprised when she does the same exact thing again. He figures this is because Arianna is only used to fighting in a dueling environment and against opponents who die after the first assault.
Live Action Television
Lampshaded & Justified with Little Pete's enemy Paper Cut, who, as one might guess, always throws paper...and attacks anyone who throws scissors with deadly homemade origami.
Worth noting is that the entire reason Rock Paper Scissors Lizard Spock exists is because of this trope; Sheldon pulled out a statistic about how players familiar with each other will keep choosing the same options, either tying or disrupting the game and that the much more complicated RPSLS will fix the problem by allowing more options.note Rock Paper Scissors Spock Lizardexisted beforeThe Big Bang Theory. Creator Sam Kass was even given a Shout-Out at least once: "All hail Sam Kass". As you can see above, it doesn't quite work out that way.
Mystery Science Theater 3000: During one host segment from The Beatniks, Joel takes advantage of the fact that both Crow and Servo have inanimate arms and hands to constantly defeat them at Rock Paper Scissors. Joel then learns the hard way that "Gypsy crushes Joel."
In Magic: The Gathering, this is built right into the game's mechanics. Each of the five colors lends itself to two or three basic strategies and weaknesses, but adding more colors to cover for each other makes it difficult to play spells reliably. On the other hand, Magic (and Yu-Gi-Oh!) allow the use of fifteen-card side decks in three-round matches, so between games you can swap out cards to counter your opponent's strategies or cover for particular vulnerabilities your opponent is hitting. Of course, nobody in the anime or manga plays three-round matches, making their extreme-theming all the sillier.
Tournament Magic is heavily based on rock-paper-scissors. Decks frequently fall into one of three categories: aggressive, combination, or control (aggro, combo, and control). Sometimes decks can play as either of two roles, but not as well as a deck truly dedicated to that role. The three roles fall into a rock-paper-scissors scenario: Aggro decks play multiple redundant threats to keep the pressure on and overwhelm Control decks. Combo decks use cards that are individually relatively weak but synergize to create powerful effects that can overcome even the strong threats from an Aggro deck. Control decks focus on defense foremost and use card-removal effects to dismantle combos — if a Control deck removes one part of a three-card combo, it cripples the whole combo, while removing one of three Aggro deck cards will leave the other two to continue attacking.
Yu-Gi-Oh! also has something like that, with Meta, Anti-Meta, and other. Meta is the best deck at the moment. it can beat any other deck except for Anti-Meta, which is designed to counter it... which because it relies on you opponents to use a certain strategy, a deck not using that strategy can beat them.
Most psionic attacks used by Psychic Warriors in Dungeons & Dragons do acid damage. Then the subversion kicks in when you realize very few enemies are acid resistant.
Some canny DMs, to avert this trope, will feed the player characters misinformation about dragons they'll be facing by abusing subversions of Color-Coded for Your Convenience. Some versions:
Player characters learn of a red dragon, stock up on anti-red-dragon equipment and raid the lair... only to learn that the townspeople are all red-green color blind (green dragons have an entirely different set of weaknesses and strengths, and spit acid rather than fire).
Player characters learn of a white dragon, stock up on anti-white-dragon supplies and raid the lair... only to learn that the dragon is actually an albino specimen of another colored dragon. Or they hear that the dragon is black (acid) and it turns out to be melanistic.
Player characters learn of a white dragon, stock up and raid the lair... and it turns out to be a wightdragon of another color.
And even discounting the DM relying on incredibly aweful puns or co-incidences, everyDungeons & Dragons true dragon from 3.0 (possibly earlier) onwards has had some limited form of Voluntary Shapeshifting, and thus could disguise themselves as another type of dragon.
Also, the Draconomicon includes dragon feats that let them swap the type of their breath weapon.
In the fangame Pokemon Tabletop Adventures, the Advanced Class Elemental Expert embodies this trope of specialization like the gym leaders from the games, but there is a payoff. First the Pokemon of that type that they own gain an experience bonus (which stacks with the experience bonus from their base class), meaning that their mon level at a very fast pace. They also gain bonuses to finding and catching that type of mon, so they can more easily gain the benefits of this class. Finally, attacks of that type deal bonus damage even if their mon isn't that type.
More Genre Savvy players will augment their team with a counter to their main types counter. For example a Steel Expert would pack a water type to counter fire, and a Bronzong with psychic moves to counter fighting types. Dark Experts will have a psychic to counter fighting, and a fire to counter steel and bug.
Occurs numerous times in Pokémon, but mainly in the earlier generations. Gold and Silver started introducing Elite Four members with dual-typed Pokémon that gave them added resistances, and in Diamond and Pearl Versions, several Trainers in later Gyms will use different types than the Gym they are in, so you can't just use a super-effective attack to plow through the whole Gym. Gym Leaders and Elite Four members in the later games will also often have Pokémon in their party, or specific moves on their Pokémon that are there precisely to counter against types that they're weak to. Therefore, if you're not careful, the one Pokémon you were relying on to sweep the entire battle could get KO'd right off the bat, leaving your opponent to mop up the rest of your party.
In Diamond and Pearl, the original Sinnoh dex lacked enough variety for some of the Gym Leaders / Elite Four to rely on their type - note that Volkner and Flint, two of the biggest aversions of this trope, fall more neatly into it in Platinum when more Electric and Fire types (respectively) were added in.
Pokémon: Battle Revolution furthers Diamond and Pearl's aversion of this. Although they tend to specialize to some degree, nearly every opponent has two or three different types represented in their team. This also applies to type-specific titles for the player. The player only needs to have three of a certain type on their team to get a unique title exclusive to each type.
The main focus of the Gym Leaders (and the Elite Four) in Diamond and Pearl is to use the move type specific to that Gym, therefore being able to have Pokémon with different typings that use the same types of moves.
Averted almost entirely in Pokémon Colosseum and its sequel. Only a handful of Trainers in Colosseum (and most are effectively tutorial fights, the only other being Miror B., a noted eccentric character) and almost none in XD (only 2 Trainers, both carrying it over from Colosseum, plus a series of Ineffectual Sympathetic Villain characters stick to such predictable teams), stick to a single type/species. Even the enemy Grunts have far more variety than typical.
Speaking of enemy Grunts, the only enemy teams whose Grunts aren't armed with the same old Pokémon happen to be Team Snagem and Team Cipher. You can expect Zubat and Rattata on any Rocket Grunt you find (replace Zubat with any old Poison-type if you want variety), and Team Galactic is similarly armed. You can also ALWAYS expect a Poochyena or Mightyena on both Teams Magma and Aqua, as well as a Fire- or Water-type, respectively. Even Team Plasma is not immune, though they're a bit closer to the Orre villains in terms of variety, but when a disturbingly large number pack Watchog...
This bit Yahtzee in the ass when he reviewed Pokémon White
Yahtzee: There was a Gym fairly early on that might as well had a giant sign saying "We use Electric types!" Every guy in the city asked me non too subtly how I was for Ground type Pokémon, and the whole area was lousy with Ground random encounters. So after grinding my newly captured Groundie lads for an hour I challenge the Gym Leader and what does she pull out? A fucking Flying Electric type! And guess what Flying types are immune to. I'll give you a hint: It rhymes with pound-ing nails into my eyesocket.
The sequel pair to these games, Pokémon Black 2 and White 2, actually warns you up front that Elesa is packing an Emolga, and that Ground attacks are useless against it, even though this time she only has one instead of the two she had back in the original Pokémon Black and White.
Pokémon X and Y does this with pretty much every Gym leader - Any trainer thinking to sweep the first Gym Leader's Bug Pokemon with the Fire-type Fennekin will sadly have to contend with her Surskit, who is not only a Water type, but is packing Water Sportnote Halves the power of Fire moves. Also, her Vivillon uses Powdernote A priority move that makes Fire attacks backfire on the user, taking a quarter of their HP and leaving Vivillion unharmed. Grant's rock pokemon respectively have Freeze Drynote An ice move that's super effective against Grass and Water and Dragon subtyping. Meanwhile, Korrina plays bait-and-switch: After many scenes hinting that she's going to use a pair of Lucarionote Fighting/Steel, weak against Ground and Fighting against you, you wind up fighting Hawluchanote Fighting/Flying, immune to Ground and resistant to Fighting instead. Got those Poison and Steel attacks to take on Valerie's Fairy Pokemon? Her first one is the Steel/Fairy Mawile, who takes regular damage from Steel and is completely damn immune to Poison!
Averted in the crossover Pokémon Conquest, Where most Warlords have a junior Warrior whose Pokemon is strong against the Kingdom's common weakness. For example, Ginchiyo's Electric types are weak to Ground, but Muneshige uses Flying Pokemon which are immune. On the other hand, each Pokemon only uses one attack, and you can see the list of enemy Pokemon beforehand, so there's no chance of them whipping out a surprise super-effective move
Sometimes subverted, sometimes played straight in Heroes of Mana. Sometimes you will face almost whole levels of enemies who use only one type, or two types that don't complement. But there are some notable exceptions: The ninjas you fight are all Ground-type units, weak against Heavy units, so they back themselves up with Flying monsters (weak against missile, which is weak against ground...). Although on one level, they send out hordes of flying units and keep them separate from their main units, giving missile units a very easy time.
Also on one late game level, 4 MacGuffins spew out units belonging to each of the four types. They can only be harmed by units that would be strong against them (ex: the flying mirror can only be harmed by missile attacks), but the other mirrors will send out monsters to attack those units, giving you a hard time.
Several raid bosses in World of Warcraft suffer from this, to the point that the encounter can be trivialized by amassing the appropriate resistance stat, even though this usually makes your other stats suffer (most resistance gear offers little to nothing in terms of offensive stats). Early raids were infamous for having an obsession with fire-based encounters (entire Molten Core, the dragon Onyxia and a good portion of Blackwing Lair (mostly dragons)), but it got more varied later on. There is even a holy-based encounter, to which there is no easy counter because holy resistance does not exist.
Also, a lot of players build their character towards using exclusively one form of magic, particularly mages. To be fair to them, it's often the only way to get a character that works. Realizing that this makes certain builds useless against some enemies, the designers introduced spell penetration that lowers resistance, and spells like the Frostfire bolt that deal multiple forms of damage to alleviate the problem. Somewhat.
Wrath of The Lich King threw this problem out the window. There are no bosses that are immune to certain types of damage - thus making double-typed attacks irrelevant (Frostfire was only useful because it could benefit from talents in two different trees). There is only one type of gatherable resist gear - frost resist. Only a handful of bosses in the expansion seriously use that type and it's not really needed even on them. The only thing you can do with that gear is to stomp frostmages in duels.
The frost resistance gear was created for one boss - Sapphiron in Naxxramas, who has a frost-based damage aura (and later Sindragosa, also an undead blue dragon of great power resurrected by Arthas). Blizzard's Monty Haul attitude towards powerful gear (and an achievement for doing the encounter without resistance gear) ensured most players just healed through it.
Since Mists of Pandaria resistance is removed from game to avoid all the problems listed above (i.e. enemies practically immune against some specific player class or need to obtain and store separate enocunter-specific gear sets). There are still some vestigial parts of in game engine, but all enemies have 0% resistance and it was removed from all gear.
Some of the opponents in the pet-battle minigame have this problem. The elemental "Spirit Tamers", for example, have very strong pets—but in some cases, those pets all use the same kind of attacks (e.g. the air elemental's pets all use "flying" attacks). This lets you field an entire team that's resistant to the attack, making the fight much easier.
Initially, the bosses in the Dinosaur King DS game embody this trope, having teams of the same dinosaur type. Later, though, they add a dinosaur of a different type into their teams - usually of a type which is strong against the type you would normally use against them-for example, a Wind boss has a Water dinosaur, which is strong against the Fire dinosaur/s that you took along on account of their strength against Wind dinosaurs.
The villains of Magi-Nation (the video game mind you) always use Core (shadow) Dream creatures, and said creatures are always the sole monsters in any of the Shadow Geysers, the Shadow Hold, or the Core itself. And since this game uses not-quite-random encounters anywhere where you won't encounter Core creatures, you can go nearly the whole game without fighting anything but them, except for two occasions. The first creature type you find, Naroom (leaf) is strong against Core types while being weak against them in turn though, so it may be a decent idea to bolster your creatures with Fire, Earth, Air or Water elements later on. Those types, meanwhile, have their own rock paper scissors, and since you'll need to grind like crazy between Shadow Geysers, you may want to have an advantage against the locals.
Entertainingly enough, on the Korean professional Starcraft scene there is a player who calls himself Rock. And he always builds Carriers (which are, surprisingly, basically aircraft carriersIN SPACE! and With Aliens), and 80% of the time he loses because his opponent knows he'll do this. The rest of the time he wins because he really is that good with the units.
A rare example where the villain takes advantage of this occurs in Advance Wars 2: one mission involves Hawke correctly anticipating that Eagle will send an all air unit force against his island fortress so he does the logical thing and surrounds it with LOTS of AA units. Thus, the player is faced with the tough challenge of destroying all his units despite having a weakness against them (not to mention Hawke's CO power, which damages ALL your units at once...).
In another mission, he keeps Eagle's Air Force out of the battle by staging an offensive next to a volcano, which air units cannot even get near to. However, he didn't seem to anticipate the skills of vehicle unit specialist Jess...
Diablo 2 characters also do this, for much the same reasons as World of Warcraft. Namely, specializing is the only way to get a character doing enough damage at the higher difficulties. As might be expected this is bad news for, for example, a sorceress who uses only fire spells who meets an enemy that is immune to fire.
Dofus's leveling system is similar to Diablo 2's and encourages specialization in a single element. Some classes are lucky enough to have damaging summons in unusual elements (The strength of summons is based of a characters level, not his stat). The prime example are Xelors and Sadidas, who get a suicide bomber summon that does damage opposed to the most commonly chosen element for the class (Xelors are usually fire, their summon does water - and has an inordinately large move range making it perfect as a counter to archers, Sadidas are usually earth, their summon does air). All classes have weaknesses, though. Feca characters are catastrophically weak to unbewitchment spells due to their shields being dispellable, Cra archers have severe difficulty fighting at close range, etc.
Strangely, and clearly unintentionally, subverted in free MMORPGMabinogi. Most, though far from all, monsters are attuned to a particular element. Weapons and armour can be enchanged with elements as well. Wearing/wielding equipment imbued with an element reduces the amount of damage taken from a monster attuned to that element; however, it also reduces the amount of damage done to said monster as well. This applies to both attack and defense, regardless of the equipment; so wielding a "fire" sword both reduces damage done to a "fire" monster, and reduces the damage taken. Likewise, it would also increase both the damage done to, and received from, an ice-attuned monster. This would appear to negate any usefulness of the element attributes; but there are only 3 elements, and the attributes are unevenly applied; so some utility is possible, although tricky to use effectively.
In the newer Persona games, the protagonist is the only one who can switch Personae. Everyone else is stuck with one, and until you can evolve their persona (and sometimes even afterwards), they're limited to a few elements and typically have a weakness that reflects that. Chie for instance, specializes in Ice attacks until you get Teddie, in which case she switches to physical, and has a weakness toward fire until you Max her Social Link. The game is aware of this, so whenever you're forced to have a character in your party (more common in Persona 3, but not unheard of in the early parts of 4) the boss will always have an attack of that type.
Of course, in The Battle with Margaret in Persona 4, a skilled Soloist can take advantage of this to get free heals!
Veterans of the Final Fantasy series know that certain types of enemies are vulnerable to specific elemental attacks. Watery or aquatic enemies are vulnerable to Lightning, cold-based enemies are weak against Fire, reptiles and fiery monsters are weak against Ice, undead and demons are typically vulnerable to Holy (and sometimes Fire), flying enemies suffer from Wind attacks, and machines or electricity-based enemies are weak against Water. Earth and Dark attacks are an exception — the number of enemies in the entire series that are vulnerable to Earth-based attacks can be counted on one hand, while Dark isn't much better off.
Which is a good thing, since spells or weapons with those particular elements are notoriously difficult to come by. However, the reverse is also true: enemies weak to Earth and Dark are very few and far between, but very few enemies are also strong against Earth and Dark, meaning that those elements are useful against enemies with otherwise powerful elemental defenses.
Unfortunately, enemies that are considered flying (which sometimes includes enemies you wouldn't expect) are generally immune to Earth damage, meaning Earth tends to be one of the least useful elements.
On top of this, most Random Encounters would have the one enemy of one type fought with four copies of the said enemy, making it a lot easier to kill them if they had a weakness. For example, the common Bomb enemy is a fire based monster weak to ice or water (depending on the game) so if you had a strong spell to exploit their weakness with and the ability to make the spell hit all enemies, you were good to go.
Treasure of the Rudra uses this trope constantly; almost every enemy focuses on one element, even though it's trivial to become immune to one and such immunity requires becoming vulnerable to its opposite. Subverted with the final boss. Wind/Lightning are opposing elements, so protecting yourself from one makes you weak against the other; the final bosses' first form is purely wind-element. Guess what element her final form (which you have no chance to change equipment before fighting) uses for her ultimate attack?
Surprisingly, the only real example in Mega Man Battle Network is the side game Battle Chip Challenge. In the regular series, most Navi bosses don't use the same chips you do, possessing their own unique attacks — and those who do use chips choose them at random. But in BCC, everybody's using the same pool of chips, and elemental bosses heavily favor chips of their own element. (This is also the only BN game with a same-type attack bonus ŕ la Pokémon.)
In Golden Sun, there are entire societies that have one of the 4 prime elements as their standard power. This isn't a choice of the characters, more something they have to deal with. But as a result, the Big Bads of the first two games are Proxians, who are all Mars (fire) adepts, and hence weak to Mercury (water) adepts. This becomes a plot point when the first game's party is able to beat their vastly stronger opponent simply because they were on top of Mercury Lighthouse, which weakened fire's power and boosted water's.
With some exceptions, enemies in the Disgaea series have a +50% strength against one of the three elements (cold, fire, wind) and a -50% weakness to another, shown visibly, so you know who to attack with which spell for maximum damage. Additionally, some maps featured enemies with the exact same weakness - Salamander's Breath was a playground for your blue mages, for instance.
One of the aversions is when certain monster-types, dragons (fire), wind sabers (wind), and warslug (ice/water), have their weak element the same as the element they absorb, making their only "weakness" the neutral of the three elements or the "StarElement."
Appears in Chrono Cross when you think too hard about it. All of the guards in Viper Manor except two of the top three are Yellow-innate. This is because they're (almost) all members of a small pool of "monsters" and "monsters" of the same type always have the same innate. However, they're all human, and humans throughout the game have all sorts of different innates, so it really makes you question Viper's hiring policy. Even certain plot characters among his guard force (Solt, Peppor, Ketchop, Zoah, and even Viper himself) are Yellow-innate for some reason. It's just begging for a task force trying to break in (say, Serge and Kid) to load up on Green elements and storm on in. Only Karsh (Green), Marcy (Blue), and Lynx (Black) seem to get away from this trope at all.
In MARDEK powerful highly elementally aligned monsters have a spell, Inversion (of that element), which deals damage to the party based on how much elemental resistance they have to that element. Come in with 110% resistance to fire? Then Inversion: Fire does 110% of your health as damage. Due to this, it's best to apply a moderate degree of elemental resistance in these battles. Also played strait with the Security Demon and Animus, both of which are almost unbeatable normally, but can be beaten with a particular trick that neutralizes much of their power.
In Age of Empires II, units tend to be strong against some types and weak against others (cavalry are good against archers but weak against pikemen) and certain factions may be better at some types of units than others, especially taking into account what their unique units are. Amusingly enough, at one point in the development, a bug in the AI of the enemies of the third Joan of Arc mission caused the AI to keep building rams until they had an army that, while unable to fight well against player units, destroyed the player's town.
Subverted in a strip of the Adventurers webcomic, in which the predictable enemy (the Ice Dragon of Ice Cave) paints himself red and convinces the party he's a Fire Dragon, and they give up in disgust (as they've spent all their resources on fire-based equipment.)
Spoofed in Nodwick after the party trashes a fire sorceress with bright red robes calling herself princess of flame or some such. After a Genre Savvy remark by Nodwick that she couldn't have made her weakness any more obvious if she tried, his party members visit the next villain's tailor ahead of time to hear about the wonderfull snow-white dress he made for her.
Web game example: The USA Rock Paper Scissors League (!) has a politically themed Flash game on its website: "Barack Paper Scissors." In the game, the player takes the part of Democratic US presidential candidate Barack Obama and plays Rock Paper Scissors against a number of other political opponents. The first opponent the player faces is former US President George W. Bush, who always chooses Rock.
Iron Kingdoms: The related fantasy miniatures games Warmachine and Hordes have "tier lists", which give the player small bonuses if their army consists only of certain units. These small bonuses are not enough to counter the fact that an army built without those restrictions is far more competitive.
Warhammer 40,000 use to have this in the form of Armoured Companies and the Chaos Space Marines "Books of Chaos". Armoured Companies are made up solely of tanks, making them all but impervious to anti-infantry weapons and, in most cases, close combat. However because it's all tanks, only a handful of anti-tank weapons are needed to utterly cripple the entire army. Chaos Space Marines had the "Books of Chaos" and "Legion Rules" which allowed you to modify your force organisation chart to gain benefits, at the cost of losing the ability to use certain units. A World Eaters Army was horrendous in the close combat phase, but only had pistols to use during the shooting phase and, apart from the then-expensive rhinos, couldn't move that fast.
Certain armies chose to fore go one skill in favour of another. Tau have almost no close combat skills but have access to some of the (then) best ranged weapons in the game. Dark Eldar traded durability for high damage output and Tyranids had no tanks and few powerful ranged weapons in favour of a vast array of powerful close combat beasts and biomorphs. For most of these armies if you can survive the phase they dominate in, you can easily decimate their armies (most painfully obvious for the Dark Eldar and Tau, as almost any damage can cripple your army).
Even with the disadvantages like losing the ability to pump out high levels of anti-infantry firepower by removing More Dakka weapons like Heavy Bolters or Scatter Lasers, gearing an army towards killing Space Marines by filling it with plasma guns, melta guns, lascannons and high armour penetration weapons will never go out of fashion simply because the majority of opponents will have Space Marine armies anyway, and for those that aren't Space Marines, all those lascannons and high AP weapons will make mincemeat out of their elite troops & vehicles leaving your elite & regular troopers facing up against their regular quality ones.
Each of the planets in Shadow Raiders suffers from this. Justified for the actual people, in that their respective cultures are forced to be that way because their entire planet is that way. Also notable in that each group of people recognizes their own weaknesses and lack of other resources, forcing them to raid their neighbouring planets - the pilot episode involves the Rock people making a water run on Planet Ice.
Planet Bone seems to be the only one who is autonomous, as their one and only weakness is apparently the stupidity of their ruling class (they seem to have little need for Fire and Rock's resources, and produces their own food). Unsurprisingly, their leader tries to betray the alliance not once, but twice.
In King of the Hill "A Man Without A Country Club", Hank makes his decision for which one of his friends gets to come with him to Nine Rivers by having them pick a number between 1 and 10. Dale immediately says "3", to which Hank admits he is right. Dale admits that he knew it because Hank always picks 3... unless he picks 5.
On Sponge Bob Square Pants, SpongeBob and Patrick are playing rock-paper-scissors with bubbles; after a while, SpongeBob realizes that Patrick always picks paper.