Fearful Symmetry

"You may know everything I'm going to do, but that's not going to help you since I know everything you're going to do! Strange, isn't it?"

—Sonic, Sonic the Hedgehog The Movie

Two identical-appearing combatants attacking in perfect synchronization with identical attacks which will often cancel each other out if the two combatants are fighting each other. A favorite of the Asteroids Monster, expect plenty of Beam-O-War if ki-attacks are in fashion, and Spot the Imposter if one of the two is an Evil Twin.

This trope runs on the rather dubious idea that since the combatants know everything the other knows they must know what they would do in this situation. This completely ignores the fact that both are facing a completely new situation (being faced with a copy of them-self) and therefore couldn't possibly know exactly how the other will react.

Compare Mirrored Confrontation Shot, Bash Brothers, and Mirror Match. May result in a Double Knockout. Not to be confused with The X-Files episode of the same name.

Examples of Fearful Symmetry include:

Anime and Manga

Neon Genesis Evangelion features the angel Israfel, which splits into two and can only be defeated by two pilots using an identical sequence of simultaneous attacks. By way of the dance.
- Not to mention the fight between EVA-01 and EVA-02 in Episode 24.
Cardcaptor Sakura does much the same with the Twin card, which can only be defeated by two allies using an identical sequence of simultaneous attacks. But with martial arts this time.
- Any fight between the two Syaorans in Tsubasa Reservoir Chronicle comes off like this, since they both use nearly identical styles of kickboxing and swordplay. The only difference is in their magic: Syaoran has inherited the Li family's magic, while the clone has stolen half of Fai's magic. The latter is also far more ruthless in combat, which generally gives him an edge.
Dragon Ball GT also features an example where the Humongous Mecha Luud can only be destroyed by simultaneous attacks from inside and outside.
- Used by Piccolo for solo training in the Hyperbolic Time Chamber.
Naruto does this near the end of the Rescue Gaara arc in Shippuuden. Clones of Gai, Lee, Neji and Tenten attack after they remove the seals that hide Sasori, Deidara and the dead Gaara inside the Akatsuki lair.
- Shikamaru's basic technique forces his opponent to perfectly mirror whatever he does. He subverts this trope in his first one-on-one fight by easily beating a perfectly symmetrical opponent. He and Kin both throw shuriken at each other. While dodging the shuriken, Shikamaru forces Kin to slam her head against a wall behind her.
Ptilol and Cyprine in Sailor Moon S were also one person split into two. They are finally destroyed when an attack from one mistakenly hits the other.
In an episode of Rockman.EXE (Mega Man NT Warrior), an evil alternate universe version of one character shows up. The inevitable fight eventually ensues. This trope is taken to the point that when the two use their Dice Bombs, they both roll the same.
In the Sonic the Hedgehog OVA, Sonic faces Metal Sonic; a robot programmed to think and fight exactly like him. Naturally, they spend half the fight simply canceling each other out. See the quote at the top of the page.
The final battle between Rushuna and Setsuna at the end of Grenadier, in which they're so evenly matched, their bullets end up intercepting each other more often than not.
- The battle between Knives and Vash in the finale of Trigun is similar in this respect.
In Mahou Shoujo Lyrical Nanoha Striker S, Subaru and her sister Ginga have a mock battle. They have the exact same fighting style and even have two halves of the same device (Revolver Knuckle), so it comes off as a mirror match—after initially looking as though a difference in skill level would dictate otherwise.
Saiyuki both plays this straight and subverts this in both the anime and the manga when an enemy creates clones of the main cast programmed with their entire moveset, with every move he's observed up until the day prior to when he chose to unleash them on the team. The main characters quickly realize they'll just copy and counter all their known moves and switch to trying different things, making quick work of the clones and rendering them a minor nuisance, chiding the enemy that created them by saying "the us you knew yesterday isn't the us that exists today". Hilariously, in the manga, although Goku, Gojyo, and Hakkai figure this out quickly, Sanzo doesn't catch on until they find him and tell him...after enjoying watching him fight against himself for a while.
In one episode of Martian Successor Nadesico, Akito has a Battle in the Center of the Mind with the ship's computer, and both combatants take the form of Gekigangar III, the title robot of Nadesico's Show Within a Show. They match each other's attacks blow for blow until Akito levels up his avatar to Gekigangar V, a more powerful robot that the computer doesn't know about.
The finale of Tengen Toppa Gurren Lagann pits the eponymous mecha against the Grand Zamboa, a twisted doppelganger created to cause despair by beating the heroes using their own shape. The Movie goes step further with Super Tengen Toppa Gurren Lagann and Super Grand Zamboa using the same Giga Drill Breaker at each other.
Pokémon the First Movie's final battle.
Shirosaki does this to Ichigo in Bleach during their Battle in the Center of the Mind. Slight subversion in that the hollow is actually capable of using much better techniques with greater finesse, he just wanted to show that he could do everything that Ichigo could just as well.
An example without the appearance part in Black Butler is the duel between Sebastian and Agni in chapter 17.
A novice tries this against Akira in Hikaru no Go. Unfortunately, as noted below, in Go you can't win by mirroring your opponent, and Akira forces him to resign.
In Yu-Gi-Oh!, Yugi and Yami Yugi fight each other using the same decks, the only exception being the Seal of Orichalcos on Yugi's side. Subverted in that after a few turns, Yugi plays Sangan, which shuffles the order of their decks, then Card Destruction to make both draw new hands.
In one of the Yu Yu Hakusho movies, Kuwabara faces an enemy who can immediately match any Ki Attack he performs, resulting in this trope. Kuwabara defeats the foe by unleashing an enormous burst of energy in order to drain both of them, and then just wailing on the guy, who is physically weaker than him.
Ga-Rei Zero at one point involves a monster whose entire fighting style is based on this. It copies the appearance and weapons of its opponents, mimics their every move, and can even reflect projectile attacks.

Comic Books

In the miniseries Infinite Crisis, both Superman and Lex Luthor face off against alternate versions of themselves, and the two Supermen (Supermans?) later take on a third version of themselves.
- Countdown: Arena is four issues of this trope, as Monarch forces different versions of heroes to fight each other.
  - However, it's not very faithful- while the Wonder Women may be hard to tell apart, the Supermen's powers are very different (one is an "evolved" Kryptonian who can grab the other two's heat vision beams and throw them around by them, while the other is the super-patriotic Superman from All Star Batman and Robin and the third is Red Son Superman, raised communist) and the others all offer some degree of variation- for example, the Ray fights a Nazi Ray and Apollo, one of the Batmen is a vampire (from Batman: Red Rain) and another is a Green Lantern (from Batman: Darkest Knight), one of the Starmen is a monkey and one is a chick, and... well, the list goes on.
In issue #24 of Archie Sonic, everybody ends up in a fight with their evil twin, but nobody's making headway because they can predict each other's moves. The good guys end up winning easily when the good Sally hits upon the idea of everybody changing partners (which, apparently, the evil Sally doesn't expect). It's not explained why, exactly, the good guys suddenly end up being the better fighters... surely this could have caused them to lose as easily as it could have caused them to win?

Film

The lightsaber duel between Obi-Wan and Anakin at the climax of Revenge of the Sith has a few moments where the student's and master's moves match each other perfectly. Including an instance of them cancelling out each other's Force Push.
- Interestingly, this has some basis in the Expanded Universe: Form V of lightsaber combat (Anakin's style) is based on the same principles as Form III (Obi-Wan's), only tailored to be more aggressive. And Obi-Wan mixes some Form V into his fighting style anyway.
Having been trained by the same tulku and possessing the same powers, The Shadow and Shiwan Khan manage to do this with bullets. But only once, because they're both a little freaked out by it.
The fight between Wesley and Cross in Wanted has shades of this, such as when they continuously deflect each other's bullets with their shots.
In Replicant, Jean-Claude Van Damme plays a serial killer and his clone grown by the government to catch him. In the climactic fight, both Garrotte and the Replicant try to hit each other but end up punching each other's fists and kicking each other's legs. The weird thing is, they actually mirror each other's moves literally (i.e. one punches with his right, while the other with his left).

Literature

In the novel, The Third Twin - the narrator notes that a brawl between the identical twins could go on for some time as they are almost perfectly matched. Ultimately subverted because it turns out they're not twins, they're clones... and there's more than one.
In Terry Brooks' Elfstones of Shannara, the Witch Sisters Morag and Mallenroh, last of their coven, are identical twins—and as such absolutely immune to each others' powers. This would seem to be a perfect excuse for the two to duke it out relatively harmlessly (which they are only too prone to do, since each blames the other for the death of the man they both loved and whom Wisp claims was literally ripped apart). Except for the fact that when their powers combine, the effects become terribly real. Both only get one shocked moment of realization to wail their agony and hatred of each other before the fire consumed them in their somewhat tragic, Karmic Death.
Forgotten Realms: Drizzt Do'Urden vs. Artemis Entreri. From the very beginning, it's clear that while they are not physically identical, when one fights the other it feels as if he is fighting a mirror image of himself.
Tahiri's internal conflict with her implanted Riina personality ends up like this once it comes to blows (in Reunion) - the two forms are literally identical, except for their handedness. Given the particular rules of this fight, it'd be equal even if one of them somehow outfought the other, as Riina demonstrates by charring herself with her lightsaber, inflicting an identical wound on Tahiri.

Live-Action TV

Charmed features a fight like this in the Mirror Universe, between the good and evil version of Phoebe and Paige. The two Paiges keep at this for some time, their specific magic causing explosions that threaten everyone around.
Arrested Development parodies this between the twins George and Oscar Bluth. each man tries the exact same sequence of movements, just to be blocked in the same way everytime.
Happens in Farscape when Crichton is duplicated. He plays rock-paper-scissors against his other self for hours at a time, and it's always a tie, even when he plays against a recording of his other self.
In a Sinbad TV series, the heroes once fought some masked opponents which mirror all their moves - and as turned out, looked like them. this is a scam by an evil wizard
In the Star Trek: Deep Space Nine episode "The Adversary", Odo and another shape-shifter fight. At one point they are fighting with exact the same moves.
In Kamen Rider Decade, the flashback to the Rider War ends with Kuuga Ultimate Form and Decade throwing identical punches at each other, creating a Sphere of Destruction. The image was iconic enough that the Climax Heroes series of video games uses it as the animation when one character attempts to counter another's Finishing Move.

Video Games

In The Legend of Zelda Ocarina of Time, the battle between you and Dark Link starts out this way, and remains this way as long as you use Z-Targeting. Unless you perform a stab at him. If you do that, instead of simply stabbing back, he'll balance on your sword and smack you in the face.
- Or instead of dropping Z-Targeting, you could use the Megaton Hammer, which is a lot more satisfying.
- Zelda II the Adventure of Link also has its Dark Link pull off the same moves as you do. It's not pretty. You can cheat and head to the corner and down stab.
An unusual sort of symmetry, though not from clones, occurs in Guilty Gear XX. Before a story-related fight, Ky Kiske and Sol Badguy both perform a massive set of attacks, with each one being the move that serves about the same purpose with each character, starting with projectiles, going next to aerial attacks, then a chain combo attack, then finally, they both throw super attacks. Everything neutralizes the other attack, and they just end up about ten feet further away from each other for it.
- IIRC, there's another version of this, possibly in GGX2#R only, where Sol and Ky clash stand slashes, chain into their "dragon punch" moves and then only Sol does his jumping EX Tyrant rave, which takes off about 25% of Ky's health before the fight even begins.
Although they don't look alike, part of the final battle between Solid Snake and Liquid Ocelot in Metal Gear Solid 4 goes like this.
One moment stands out in particular. After spending several minutes beating each other to a pulp, Snake and his "brother", Liquid Ocelot, each find themselves facing each other and holding a syringe full of fast-healing nanotech. Instead of jumping back to inject themselves or trying to knock away the other's syringe, they inject each other, knowing that the the other will do the exact same thing. Fearful symmetry, indeed...
- That was a homage to the fight scene in The Twin Snakes between Liquid and Snake, who were twins... snakes.
Something similar can happen in Street Fighter Alpha 3. Adon (trained under Sagat) has a special intro with Sagat, where they both do identical kicks that end up parrying each other.
- Alpha 3 also has Fearful Symmetry intros for Evil Ryu versus Akuma (both trigger the Raging Demon special move, and the screen whites out as they exchange blows before being forced apart) and Akuma versus Gen (Akuma triggers the Raging Demon, Gen blocks each hit, Gen rushes past and triggers his own multi-hit move, Akuma blocks each hit).
The cutscene fights between Luke and Asch in Tales of the Abyss; note that they were both trained in swordfighting by the same person, with a side helping of Cloning Blues involved. Helped by the fact that Luke is left handed where Asch favors his right.
- This is probably best exemplified in their first, intended-to-be-lost Duel Boss fight. If Luke and Asch use Raging Blast or Rending Thrust at the same time, a mini-cutscene plays where the two smack each-other simultaneously.

Luke: "Damn! We keep using the same Arte!"

Asch: "Because you're a Replica!"

The battles between Dante and his older twin brother Vergil in Devil May Cry 3; both utilize their agility, stamina, big-ass swords, and Devil Trigger abilities.
- From the same game, Dante's doppleganger battle is a more straight-on example.
- In the original, this is played even straighter with Dante and Nelo Angelo (who is Vergil, albeit Brainwashed and Crazy). Nelo Angelo plays the role of Mirror Boss, using the exact same sword swings and martial arts combinations as Dante (except for the fact that he has a much longer reach). In fact, part of the key to defeating Nelo is parrying his attacks with precise swings from your blade and then countering while he's caught off-guard and trying to ready another go.
- In 4, the battles against Dante himself involve Nero having to fire at him (the boss deflecting your bullets with his own shots) while approaching and then quickly attacking while he's open (preferably via Devil Bringer). This even causes a shift to a quick time event where the two square off with their swords before Nero tries to overpower his foe.
Jaster Rogue's darker (and should I say hotter?) doppleganger in Rogue Galaxy.
A variant occurs at the end of Terra's story in Kingdom Hearts: Birth By Sleep. After Master Xehanort possesses Terra, and the Lingering Sentiment forms, the two fight. Terranort has the same appearance as Terra (golden eyes, darker skin, and white hair notwithstanding), but most of Terranort's moves are ones Terra can acquire.
The PC game based on The Death Gate Cycle has one of these as a puzzle. You face a mirror image of yourself, and since he copies everything you do, you can't move forward since the double is in the way. You get rid of him by casting a suicide spell backwards, which does nothing to you, but the re-reversed spell cast by the double kills him.
In Mega Man 1, the title character has to fight a robot clone of himself. While his movement is his own, the robot will fire a shot every time Mega Man does.

Web Original

"Insanity Prerequisite" in the Whateley Universe: protagonist Carmilla fights Cosmic Horror demon The Kellith. Since they're just two different aspects of the same person/thing, it gets complicated.

Western Animation

Also the title of a Justice League Unlimited episode where Supergirl fights an older, more powerful, and more ruthless clone who knows all her moves.
- Likewise, in "Divided We Fall" the original 7 leaguers all fight the Brainiac/Luthor hybrid's copies of the Justice Lords.
  - Lets not forget "A Better World" in which the entire Justice League fights alternate versions of themselves. The Batman vs Batman conflict plays this trope to the letter with the mirror Batman insisting he knows everything Batman will do (and for the most part being right)
In the Futurama episode "The Farnsworth Parabox", the two Leelas do this, to no effect. After they lunge at each other and end up simply colliding in midair, one of the Professor Farnsworths tells them "Now, now, perfectly symmetrical violence never solved anything."

Leela: "We're exactly the same! I know all her moves; therefore I have the upper hand!"

- Also from Futurama is Flexo, a bending robot exactly like Bender. Whenever they get into a fight, they throw punches and just end up hitting each other's fists.
The final battle between Zuko and Azula in Avatar: The Last Airbender definitely has these moments, often with red and blue flames mirroring perfectly.
In Xiaolin Showdown, Clay ends up fighting a mime who can perfectly mimic his movements. Clay responds by punching himself; Clay can take the hit, but the mime can't.
In Aladdin: the animated series when a Trickster called Chaos pairs Aladdin against an Evil Twin the results are to be expected.

Chaos: Well this is certainly exciting; it's like he's fighting a mirror.

Other

Happens in competitive card games like Magic: The Gathering and Versus a lot, especially at the start of sanctioned tournaments where many players may be using identical decks that did well in previous tournaments due to the existence of websites dedicated to the best builds. Many tournament players have several silver bullets against their own deck in their optional side-deck to use in mirror matches.
- There are also a few pairs of cards that seem perfectly matched to one another - for instance, Time Spiral reprinted the 13/13 Krosan Cloudscraper, and the next set (Planar Chaos) has Shivan Meteor, which deals exactly 13 damage.
When playing black in a game of chess, one possibility is to simply mirror white's moves. This is sometimes called a Russian game.
- However, this is extremely easy for white to foil, as all that needs to be done is give a queen or rook a clear path to the opponent's side of the board. If black mirrors, all white has to do is kill the other queen/rook; that piece then can't mirror it, since it's no longer on the board.
- The Russian Game (1. e4 e5 2. Nf3 Nf6) is both an example and a subversion. Black mirrors when you wouldn't expect him to (2... Nc6 is usual) but he gets into trouble if he continues mirroring (3. Nxe5 Nxe4?) There are, however, other openings where mirroring can continue for the first ten moves or beyond.
  - Subverted in Go. Sure you can try mirroring your opponent. But it never works in a center game where it is always the first person that plays that ends up winning because they can complete their circuit before you complete yours.