Gabe: Well, isn't the enemy of your enemy, like, your friend? Or whatever? Can't they team up? Tycho: Not exactly. In thissetting, the enemy of your enemy is still a floating, greasy, armored brain. Gabe: Well, what about his enemy? Maybe you could be friends with him. Tycho: No, because that guy is a mechanical horror in an undying battle shell. He sails from world to world in a flying tomb, serving gods who eat hope.
This is any fight where there are at least three sides involved, with no prearranged alliances.
We can be talking individuals or armies, although the version with the individuals is usually more fun since the army one often degenerates fast into a free for all. Often noted by directors and fight coordinators as being very difficult to set up or film properly, although often worth it for the aforementioned fun if they manage to pull it off right.
Almost always begins as a Mexican Standoff as the various sides try to figure out who to shoot or stab or fireball first. Things get particularly fun if you have several guys with a gun in each hand, each trying to keep aim on the other two targets simultaneously. Expect a lot of sweating, twitching, and flicking eyes until the inevitable happens.
This trope calls for no prearranged alliances because then it's not really three-sided — unless there are so many sides involved that even taking prearranged alliances into account, there are still at least three sides! However, it is fairly common that after a short amount of fighting, two of the sides will accidentally or on purpose end up ganging up on the third, often with an unspoken agreement to finish dealing with each other once the third side is out of the way.
Often enough, this alliance will be helped along when the third side assumes that all its foes are on the same side.
Alternatively, if neither side can win the battle on their own, the outcome depends entirely on whom the weakest of the three will ally themselves with, resulting in the Kingmaker Scenario.
Alternatively alternatively, a particularly devious side may manipulate the others into Let's You and Him Fight, then go after whoever's left.
In a video game, especially a First-Person Shooter, 99% of the time, the 3 sides will consist of the player and any allies vs. enemy soldiers vs. some sort of mutants/aliens/zombies.
The trope name comes from the French phrase "Ménage à trois" which basically means a threesome. Who knows if that's connected to what this trope means.
No real relation to Super Smash Brothers Melee, although that trope appears quite prominently in that series as a whole.
Compare Gambit Pileup, which is like this trope but with gambits instead of fights.
Zeta Gundam: Titans vs. Axis Zeon vs. AEUG. The most memorable of the Free for Alls, homages of this set-up continue down to Gundam 00.
Gundam ZZ briefly dabbled in AEUG vs. Zeon vs. Blue Team during one episode, but that was quickly swept away once the titular mech showed up. However, at the end of the series it does essentially become a showdown between the AEUG, Neo Zeon, and Glemmy Toto's faction of Neo Zeon.
Gundam Wing: Gundam Team vs. World Nation vs. White Fang (though eventually, the Gundams decide to side with the World Nation, mainly because White Fang is the actual threat)
Gundam X: Vultures vs. New United Nations Earth vs. Space Revolutionary Army
Gundam SEED: ZAFT vs. Earth Alliance vs. Orb the Three Ships Alliance
Subverted in Gundam SEED Destiny, in which, in the final episodes, ZAFT defeated the Earth Alliance, and after that, the Three Ships Alliance defeats ZAFT.
Gundam 00: At the start of the series, the main conflict would be between the three major power blocs of the Union, the HRL, and the AEU. Also known in modern times as the United States, Communist Russia and China, and the European Union, but mostly actually just small conflicts in the Middle East in countries supported but not formally belonging to any one of these and no major war.
A variant of this exists twice in Gundam AGE. First, we have Zalam and Euba fighting each other, with Flit fighting to stop Zalam and Euba from fighting, and later we have the Diva's crew who wants to destroy the UE, the corrupt Earth Government who wants to capture Grodek and the Diva, and the UE who just seems to be killing everyone they see mercilessly...
Jubei Chan 2 has this; Jiyu vs. Freesia. vs Kita. Kita was the weakest of the 3, but Jiyu and Freesia couldn't ever focus on him because of each other. That is, until the end, where he gets possessed by the spirit of his father. By then, though, the two Jubeis have made up.
Pulled off near the beginning of Liar Game... actually, most of the time.
About two thirds of the way through Death Note, following the end of the original Light vs. L feud, two new characters are introduced: Near, replacing L as the new mind-gaming uber-sleuth, and Mello, a criminal mastermind. All three have very good reasons to eliminate the other two, although Near and Mello's relationship is a tad more confusing, and Light treats the whole thing as an extension of fighting L.
At the end of Outlaw Star, Gene and the crew of the Outlaw Star vs. the MacDougal Brothers and Gwen Khan vs. the Kei pirates. The C'tarl C'tarl Empire also shows up outside the Leyline, but is unable to get in.
Naruto: Tsunade vs. Jiraiya, Shizune and Naruto vs. Orochimaru and Kabuto. Although Tsunade takes up Jiraiya and Naruto's side more or less right away, she does first poison Jiraiya.
One Piece situation: Whitebeard and his entire fleet is attacking Marine Headquarters, where the Admirals, Seven Warlords of the Sea, and all the important Marines have gathered. Luffy just brought in the Impel Down convicts. Also on board are Crocodile, Buggy, and Jimbei, who do not feel any particular loyalty to him. Meanwhile, Hancock is attacking everyone. Luffy just had a chat with Whitebeard and while they are not working against each other, they are not working together. Luffy also basically declared his hostilities towards Whitebeard even as he protected him from Crocodile, who attacked him because he probably killed Crocodile's crew or something. The remaining Warlords are all practically factions in themselves. It's hard to tell just how many factions are actually fighting right now, and for whom. In the end, another faction, led by Blackbeard, shows up so that Blackbeard can take Whitebeard's power and use it to destroy Marineford, and yet another faction, led by Shanks, shows up to end the war. All in all, there's at least five different factions, with individuals breaking off from their group to do their own thing in the middle of all of this.
The Survival Game in Skypiea is a struggle between three factions; the Straw Hats, who want the gold, the Shandians, who want to reclaim their homeland, and Eneru's minions, who want to see who is worthy to go to Endless Vearth. The Ordeal of Iron features Zoro and Gan Fall vs. Wyper and the Shandians vs. Ohm and the Enforcers vs. a giant snake that swallowed Luffy, Nami, and Aisa.
In the Water 7 Arc, while Luffy and Franky are fighting each other over their respective grudges (Luffy has a grudge against Franky for attacking and robbing Usopp, while Franky wants revenge against Luffy for destroying his house), the Galley-La shipwrights attack Luffy because they believe he sent Robin to shoot Iceberg, and attack Franky for getting in the way, as he doesn't appreciate their taking on Luffy.
In Code Geass: Nightmare of Nunnally, most of the battles involving Nunnally have this, with Britannia trying to suppress the Japanese, the Japanese trying to defeat Britannia, and Nunnally trying to stop the violence.
In Bleach's Bount arc, Byakuya and Ichigo fight Kariya, but Byakuya doesn't seem to care if he hits Ichigo with his attacks, so it looks like this trope at times.
Volume 15 of To Aru Majutsu no Index is this. Five organizations from the dark side of Academy City made up of four people each fight it out. Add in how three of the groups have Level 5's, one group hires 5000 mercenaries, and a subordinate of one of the organizations rebels, and you have one book practically made of Crowning Moments Of Awesome
Battle Royale has aspects of this, both of the indirect type and the very direct type. There are several "groups" involved- Mitsuko, Kiriyama and 3 or 4 minor characters,all out actively hunting all the other students (and thus, each other), although 3-way confrontations are rare. However, there is the moment when Kyoichi confronts Shuya/Noriko, and Shogo appears, aiming at them both (although mainly at Kyoichi, because he has clearly snapped. And, obviously, who could forget the Melee a Cinq/Six in the lighthouse?
Sannin shogi is a kind of chess with 3 players playing against each other. However, an alliance is automatically formed if two players gang up on the third.
Diplomacy features seven sides, and the only good way to get an advantage is by convincing other players to join with you in ganging up on somebody else. Since the rules are explicitly designed to allow you to lie to other players about what you are going to do in your next move, things quickly get crazy. Many players have remarked that playing Diplomacy is a good way to ruin friendships.
And that's just the original; many variants can have up to eleven players, but these boards tend not to be as balanced as the original, so some countries are doomed from the start, unless the player is exceptionally good.
This is actually quite common in board games, whether the games range from simple to mind-bogglingly complex. Consider Risk and its variants, Twilight Imperium, Dirk Henn's Shogun, and dozens of other examples. Heck, even a lot of games that prohibit direct conflict, like Settlers of Catan, Monopoly, etc., allow for the same dynamic as this trope — if you excuse a broad enough definition of "conflict".
There's a format in Magic: The Gathering, which appropriately enough is called "multiplayer chaos", which consists of at least 3 players against each other, with no predetermined alliances, and no rules saying you must adhere to alliances you make over the course of the game.
The card game Munchkin in all its forms lives and breathes this trope. Although it can be played with only two people, it works perfectly fine up to six with just one box set, and even beyond if you have enough expansions, all of which are a side unto their own.
Also by Steve Jackson, the game Illuminati isn't any fun with fewer than three players. Players can support each other's attacks and defenses, and sides will change rapidly as players approach their respective goals.
Speaking of poker, the Deadlands CCG Doomtown (which uses a poker mechanic to resolve shootouts) can be played this way.
The great big battle at the end of Lucifer is between Lucifer, allied with the angels of the Silver City, and Lilith's faction. Halfway through the battle, Christopher Rudd appears leading an army of demons and the damned combined. When his general asks who they're attacking, he responds, "Both. We attack both."
In one issue: Sonic vs. Scourge vs. Shadow vs. vs. Amy vs. Rosy vs. Rob 'O vs. Metal Sonic vs. Silver... with absolutely no real clear way to tell who's fighting who and when.
Though it quickly turns into everyone vs. Scourge when he turns Super.
At issue 162-164, an all-out battle for the crown of Acorn was fought between The Freedom Fighters, Mammoth Mogul and the Destructix, and Ixis Naugus and the Arachne. Naugus joins with Mogul during the battle when he was told by him that Mogul was the founder of the Order of Ixis, turning the battle into a simple two-sides war. The battle was interrupted by Dr. Eggman, however, and he captures Mogul, Naugus, and their forces back to his capital prisons. The Freedom Fighters won, but at the cost of Sir Connery.
And during one of the Sonic Universe arcs, we end up with Team Rose (Amy, Cream and Cheese, and Blaze), Team Dark (Shadow, Rogue, and Omega), Team Hooligan (Nack, Bean, and Bark), and the Babylon Rogues all fighting each other over a Sol Emerald. Teams Rose and Dark briefly team up, but by the end of the story, it quickly devolves into a four-way battle.
In Throne Of Atlantis, the battle is initially between the Justice League and Ocean Master's Atlantean forces. Then the Trench are freed from their watery prison and attacks both sides. When Aquaman becomes king again, he orders Atlantis to ally with the League and fight the Trench.
In Aeon Natum Engel, the escalation of the Iceland invasion led to NEG vs. Order vs. Migou. Then Moloch showed up.
In the Danny Phantom/Teen Titans crossover fic HIVEMinded, Jump City ends up as the sight of a brawl between the HIVE, Plasmius' army of ghosts, the Guys In White, the Titans, and the local police forces. Oh, and then the Justice League sends a few members to try and help, but that doesn't work out so well.
Shinji And Warhammer 40 K has a Gambit Pileup with Shinji vs. Gendo vs. SEELE vs. Kaworu. This eventually culminates with an actual melee between NERVs EVAs and Magnos Tancred vs. Kaworu's Warborn vs. Keel Lorenz's MP EVAs, although Kaworu temporarily joins Nerv.
In the Naruto fic Hakumei, the heroes return to Konoha to help La Résistance rebel against Danzou... on the same day as the Sand/Sound Invasion, which occurs more or less as in canon. No one realized in advance that there was more than one conspiracy ongoing, so the eventual three-way battle is not good for anyone's plans.
"We're only missing a joint Kumo-Iwa invasion and then everyone will be represented."
Queen of All Oni: The fight in the shrine of the Three Shades — the J-Team goes there looking for information about the Shadowkhan, the Shadow Hand follow them so that Jade can steal a powerful Shadowkhan artifact, and the monks are duty bound to protect said artifact (one tablet of a Tome of Eldritch Lore). Of course, since the monks are all True Neutral, they interpret "protect the artifact" as "fight anyone who shows up who isn't there to join the order", so even though they and the heroes are technically on the same side, they fight both them and the Shadow Hand. And it should also be noted that this fight is a total Curb-Stomp Battle, as the monks utterly wipe the floor with the other two sides.
Likewise, the fight over the second tablet in the Vault of Endless Night is between the J-Team, the Shadow Hand, and the various evil creatures sealed down there. This time around, the heroes are at least aided by the local guardian (a giant feathered serpent called Nameless), who joins forces with them the moment he realizes they're not evil. The Shadow Hand still wins however, managing to grab the tablet and get away at the last minute.
The Evangelion/Metal Gear Crossover Evangelion Gear has a three-way war between The Patriots (led by Big Boss), NERV (led by Gendou Ikari), and SEELE (led by Keel Lorentz/Major Zero).
Nobody Dies is escalating into this, with humanity (NERV) vs. the Angels vs. the Cherubim. No one's entirely sure where the newly-unveiled Grigori fit into this, and there's even another faction of Angelic beings, the Seraphim, who have taken notice of the conflict on Earth but have thus far not done anything directly. And to make things even more confusing, a few of the Angels appear to have their own agendas, which may or may not tie into the above conflict.
The Harry Potter fanfic The Return of the Marauders features a very elaborate three-way conflict between Harry's Marauders, Voldemort and his Death Eaters, and Manipulative Bastard Dumbledore and his Order of the Phoenix. Among other things, double agents abound.
The Lake Trot Crisis started as the Celestine Junta attacking the Hyracotherium Republic and Kingdom of Unicorns for control of said lake. Then Wind Whistler kicked off her coup, which led to the troops loyal to her attacking those loyal to Sullamander; both the Earth ponies and unicorns decided to take advantage of this to take more territory for themselves, and started attacking each other as well as the pegasi.
The Winter War wasn't supposed to be one of these — nominally, the Republic and Kingdom were allied against the Junta. However, only the Royal army obeyed that; the nobility's mercenary forces splintered, with only some fighting the Junta, some fighting the Republic, and some fighting everyone for the sake of riches.
Turnabout Storm gets a courtroom version during Gilda's cross examination when the defense, the prosecution, and the witness all start to verbally smack one another, prosecutor-witness relations be damned. Since Ace Attorney's courts run on Mundane Made Awesome, the overall treatment is not that much different from a physical version.
Judge: A three-way tussle between the defense, prosecution and witness! My! How exciting! Er- I mean... ORDER!
In The Swarm of War, the first arc has: 1)The King’s Army. 2) The Loyalist Space Marines and Duke Verin’s forces. 3) Judanus with his Chaos Marines and cultists. 4) Bugklaw with his Orks. 5) The Swarm.
Films — Animation
Princess Mononoke: no less than eight distinct factions, what with San and the Wolves, Ashitaka, Eboshi and Irontown, Jigo and his hunters, the Boars, the Apes, the Deer God, and Asano's samurai. All at cross-purposes. Of course, they aren't all actively trying to kill every other faction, but the resulting tangle is pretty impressive.
Batman: Mask of the Phantasm is largely a three-way conflict between Batman, the Phantasm, and Joker, as demonstrated by this◊ nifty color guide. By the time they're all gathered in the same place, though, Enemy Mine has come into effect.
Pokémon: The Rise of Darkrai, which has the original Japanese title of Dialga vs. Palkia vs. Darkrai. Basically, Dialga and Palkia are having a territorial feud (the reason for which wasn't revealed until two movies later), a battle which they incidentally bring to the town of Los Alamos, Darkrai's home. Darkrai has to protect the town from the two Olympus Mons' rampage, making him the hero of the movie.
Pirates of the Caribbean: All of the movies have some point or another where this sort of thing happens. It's almost always Pirates vs. other Pirates vs. Country (Spain or Britain). Or all of them against Jack Sparrow, because he's just so likeable.
Dead Man's Chest: Will Turner vs. Jack Sparrow vs. James Norrington, with Elizabeth standing disgusted on the sidelines. Notably, does not feature two of the sides joining temporarily. Unless you count Will and Norrington both attacking Jack and ducking out of each other's way, but that doesn't last long.
At World's End begins this way (Barbossa's pirates vs. British Redcoats vs. Sao Feng's pirates), but the two illegal factions quickly postpone their differences for a later date.
On Stranger Tides: Blackbeard's crew vs. Barbossa's crew vs. the Spanish for control of the Fountain of Youth, with Jack caught in the middle.
The original Dawn of the Dead has a climactic 3-way fight between Peter, the zombies, and the bikers invading the mall.
A very short but awesome fight happens between Yuen Biao, Sammo Hung, and Jackie Chan in Dragons Forever.
The famous climax of The Good, the Bad and the Ugly is a Mexican Standoff between the three eponymous leads, well-known enough that almost half of it is in the theatrical trailer, although it stops short of showing the outcome. Although a picture of the scene would make a good trope-picture, it turns out to have a minor subversion since The Good had unloaded The Ugly's revolver, so he knew there was only one threat on the field. But since the viewers and the other two combatants didn't know, the delightful tension before the battle was still there.
Parodied in the film Anchorman, when a brawl between rival news broadcast teams escalates to ridiculous levels as all the other stations in the city show up one by one.
In The Matrix Reloaded, Morpheus and Trinity vs. the Merovingian's twin wraiths vs. two Agents, during the highway chase involving the Keymaker.
In The Matrix Revolutions, it was the humans vs the machines vs Smith and his clones.
Millionaire's Express is a 1986 Hong Kong movie that appears to juggle a complex set of storylines... until the final 25 minutes or so, when the movie erupted into an all-out anarchic brawl spanning an entire town and involving some of the biggest names in Hong Kong movie asskicking at the time: Sammo Hung, Yuen Biao, Hwang Jang Lee, Cynthia Rothrock, Yukari Oshima, Corey Yuen, Dick Wei, Richard Norton, Lam Ching-ying, and Yasuaki Kurata among them.
Of course, it's not entirely clear why the other assassins go at each other, since they're on the same side.
Presumably, the guy who takes out 47 gets the bounty on his head.
District 9 has one around the climax. Wikus and his Mini-Mecha versus the MNU Mercenaries versus the Nigerian Gangsters.
The fight on the baseball field between Jason, Duncan and Charlie in Mystery Team.
During the climax of The Dark Knight, Batman has to take on the Joker, along with his goons and dogs, while simultaneously incapacitating S.W.A.T. officers who have been fooled by a Disguised Hostage Gambit. Saying the S.W.A.T. officers don't cause much of a problem would be an understatement, however.
Earlier in the film, the Joker sets one of these up between three goons, forcing them into working for him, but claiming that only one spot is open and holding "try-outs". He leaves a broken pool cue in front of them and leaves, telling them to "Make it fast."
Killer Elite. The hitman protagonist Danny is tied to a chair by his antagonist, ex-SAS man Logan for interrogation and killing. A third party then enters and takes Danny prisoner, binding his hands behind his back. This leads to a three-way fight involving two bound badasses trying to kill their captor and each other at the same time.
In one of the Discworld books, a good Dwarf brawl is described as having "100 participants, and 150 alliances."
In Sandy Mitchell's Ciaphas Cain novel The Traitor's Hand, the fight against the Chaos forces is greatly simplified by the fact that two separate Chaos factions are on the planet. At the end, Cain follows Chaos Space Marines to a ritual they are trying to disrupt; the Marines clear their path.
In Dan Abnett's Ravenor, there are the forces trying to summon a daemon, the forces trying to exploit Enucia, an evil language, and then the Inquisitor Ravenor and his retinue. When the daemon-summoners try to assassinate one of the language forces, Ravenor watches it psychically, making the target assume he had been behind the plot.
In the Green Rider series by Kristen Britain, there's a board game called Intrigue which is considered best played with three players in a Mêlée à Trois type game.
C. J. Cherryh's Downbelow Station features a war between Earth and the rebel Union that becomes three-sided when the Stations and Merchanters, caught in the middle, form an Alliance so as not to be sold out in a peace treaty between the other two.
The Hobbit has the Battle of Five Armies: Elves and Lakemen vs Dwarves vs More Dwarves vs Orcs and Wargs. Gandalf intervenes to get the dwarves to ally with the elves and men right at the outset, however. Other semi-independent factions that join the goodies later on include the Eagles and the Bears of Bjorn.
The central plot conflict of Atlas Shrugged has three sides: the strikers, the scabs and the looters.
A Song of Ice and Fire features a great number of factions fighting each other, each with their own point of view justifying their actions. This is most overt in the War of the Five Kings, which is Exactly What It Says on the Tin. Even after that war grinds down, new factions rise up or splinter away.
In the Warhammer 40,000 novel Deus Sanguinius, a battle between the Blood Angels still loyal to the God-Emperor and those who have thrown in with Arkio is complicated when Word Bearers Chaos Space Marines join in.
Any Matthew Reilly book will probably have at least one of these. Most of the battles in Scarecrow turned into these, with the heroes repetedly fighting 3 different mercenary armies, as well as whoever they were trying to fight in the first place.
Volume 15 of To Aru Majutsu no Index has a Battle Royale between the five underground organizations of Academy City: GROUP, ITEM, BLOCK, MEMBER, and SCHOOL, with each having their own goals and motivations.
Harry Potter and the Order of the Phoenix has the Death Eaters versus the Ministry of Magic versus the Order of the Phoenix. No group likes any of the others very much. Later, the first two groups become one and the same.
At the end of the book Pearls of Lutra, it's Martin II, Grath, and the other heroes vs. Emperor Ublaz and his monitor lizards vs. Rasconza and his corsairs.
And in Triss, it's the good guys vs. Princess Kurda and her vermin vs. three giant adders.
Nineteen Eighty-Four had Oceania, a totalitarian empire consisting of all of the Western Hemisphere plus Great Britain and the southern half of Africa, fighting Eurasia, essentially Soviet Russia and Continental Europe, fighting Eastasia, a cultist union of China, Japan, Korea and Northern India. They usually united against each other, but also betrayed each other just as easily. Of course, they are almost indistinguishable apart from location and language.
In the Conan the Barbarian novella The Flame Knife, what starts out as Conan and a handful of Zuagirs besieged by Yezmites winds up as a pitched battle of Yezmites vs. Kushafis and Zuagirs, then a massive engagement of Yezmites, Kushafis and Zuagirs vs. the Iranistani army, and finally a route of Yezmites, Kushafis, Zuagirs and Iranistanis as they flee the city and a horde of ghouls eager to devour all four human forces.
Mystery Science Theater 3000 episode Warrior of the Lost World features a big fight meet between the various rag-tag gangs who eventually team up to overthrow the evil Empire.
Sheridan's forces in Babylon 5 engineer one of these against the Vorlon and Shadow fleets.
Jon Stewart, Stephen Colbert, and Conan O'Brien staged one of these over who was ultimately responsible for Mike Huckabee's political showing. This one did start with an alliance, between Stewart and Colbert, but that was quickly abandoned because the true Mêlée à Trois is funnier.
The Colbert Nation provides an alternate name for this one: menage a awesome. (Let the record also show that the whole thing was concocted as a way to "waste time on all three of our shows" during the writers' strike.)
Buffy the Vampire Slayer: In one episode, a fight breaks out between Buffy vs. a cowboy vampire vs. a horde of innocent bystanders under mind control by a demon. Buffy and the vampire don't actually team up, but they do take a break from fighting each other to focus on the bystanders. A person just tuning in might think they were on the same side.
LOST was, for its first three seasons, a conflict between the Oceanic flight 815 crash survivors and the mysterious Others. However, the survivors essentially wiped out the Others in the season 3 finale, just as the third combatant, a freighter with a mercenary team sent to kill everyone on the island, arrived. Both the survivors and the Others had separate conflicts with the freighter, though by the end of season 4 the survivors and Others had teamed up and successfully repelled the freighter.
Stargate Atlantis developed a three-cornered fight between the Atlantis team, the Wraith and the Asuran Replicators. Although there was never a three-way battle; the closest is when Atlantis pulled an Enemy Mine with the Wraith to take out the Replicators.
The bizarre abusable child music video addition: What looks like the entire lineup of Cobra Starship does one of these with hidden pies around a table piled with cash in the music video for "The City Is at War". This doesn't really constitute a pie fight, however, as they're meant to be basically gun/knife stand-ins, with being pied in the face being a cause of death.
Occurs rather often in Professional Wrestling, in the form of a "Triple Threat Match" or "Fatal Four-Way" (those are the terms used by WWE), or the "Three/Four-Way Dance" (as ECW called it).
Ring of Honor uses a combination "four-way" and tag match (separate from a four-way tag team match with eight participants) called "Four Corner Survival," where either of the two 'legal' wrestlers can tag in either of the two wrestlers but only one can win (which is just a cooler name for the old "four corners" match).
Matches can go from Triple-Threat Matches to Fatal Four-ways to Six-Pack Challenges to full scale 20-60 man Battle Royals.
This is basically how it looked like the InVasion storyline was going to play out. To sum up: after the WWF (later WWE) very publicly buying out WCW, it turns out that Shane pulled some last-second shenanigans and now "owns" it, and a massive WWF/WCW feud builds up. Suddenly from left field comes Paul Heyman and the ECW Originals, sick of playing second fiddle to the Big Two, especially since their buy out was far more low-key and basically ignored while their wrestlers were quietly filed into place. But then, it turned out he was just The Dragon to Stephanie, who was in fact allied with Shane against Vince, supposedly set-in-stone contractual alliances changed almost on a weekly basis, only a handful of people from either ECW or WCW were saved from becoming jokes, and by the end of it most folks would rather just forget it ever happened.
Most of the factions above also spend a lot of energy on internal squabbles: the Imperium is constantly engaged in insurrections and reconquests, the Eldar have a break-off group of evil counterparts who prey on the other Eldar as much as any other race, the forces of Chaos are divided amongst rival gods, and the Orks will happily fight each other if there aren't any other enemies available. Not even the Tyranids and Necrons are immune to this in-fighting; the former is controlled by a Hive Mind that will occasionally run survival-of-the-fittest tests on itself, and the latter has recently been broken up into multiple rival "dynasties", some of which are lead by rather... damaged individuals.
During the storm of chaos in Warhammer Fantasy Battles the Empire is fighting the forces of chaos led by Archaon. Then Grimgor and his orcs turns up, fights their way through both forces, kills the chaos leader to prove that he is the best and goes away— leaving both forces badly damaged. Most worldwide campaigns pit everyone against everyone though. Old Imperium motto used by fans: "The enemy of my enemy is the next one to die.
In general, the forces of Chaos are locked in the four-sided variety of this trope. There are four Chaos gods, and a given Chaos warrior is aligned with one of them and opposed to the other three. The key is getting the four sides to stop fighting long enough to actually accomplish something. But hey, at least they get an army of Demi-Gods by feeding thousands of raw recruits to their chosen champions.
In the setting of the RPG Cthulhu Tech, the Aeon War is a grand Mêlée à Trois between the New Earth Government, who want to live; the alien Migou, who want humanity to die so they don't learn more of the mythos and accidentally wake up the Old Ones; and the Cults of the Old Ones, who want the Old Ones to wake up which would result in the death or massive alteration of everyone else. It's a fun time all around.
Paranoia has the official agenda of The Computer, the clandestine agendas of over a dozen secret societies, the office politics of several service groups, plus the personal goals of six PCs and as many NPCs as Friend Gamemaster can keep track of. Any two of these may sort-of-align at any given moment (in the sense of "yes, this person will screw me over, but this other person will screw me over faster and harder"), or may pretend to do so. Some official missions up the ante by having everyone pursue the same MacGuffin at once.
Since even the heroes of the setting are professional domestic terrorists, Shadowrun tends to turn into this. Corps hire runners to do their dirty work and even if a lot of runners shun wetwork (outright assassination contracts), they aren't above sabotage, bombings, espionage, theft, and occassionally offing some security guards if things get messy. As a result, runners tend to be grey-area men and women working for bad people against other bad people. Other teams of runners rarely cooperate past a pulling a big job together and many will betray eachother for the sake of a bigger cut.
To quote one book's fluff: "The only mate a runner should trust is himself... unless some corp brainwashed him into one of those sleeper sorts who go blow themselves up when they heard the phrase 'warm bacon'. Then he probably would be best off not trusting himself either."
The Mahri Nui saga in BIONICLE has five sides fighting over the Mask of Life: The Toa Mahri need it to save the world, the Big Bad Makuta also doesn't want the world to die but the Toa (justifiably) don't trust him, the Barraki want the mask because it can reverse their mutations and allow them to try conquering the world again, Hydraxon thinks it's too dangerous and must be destroyed, and a Gadunka beast is just territorial.
Not to mention that the Mask passes from person to person in the conflict, and some of the Barraki decide to just go solo and escape, leading to an internal conflict within the Barraki group as well. Brutaka arrives at some point to fight Makuta, for reasons of his own. The mad ruler Karzahni also got an interest in the Mask after hearing about it, but he never to join the conflict as he was defeated and taken captive by Lesovikk in a side-story.
Three-way firefights between Gordon Freeman, the marines, and the aliens were one of the defining attributes of Half-Life. Usually, the marines were ahead.
It happens in scripted sequences too, to remind you that yes, there is a battle raging. For example, three Alien Grunts get dropped off by a Xen Flyer only to be immediately bombed by a F-16.
In Half-Life 2 and the Episodes, it becomes Human/Vortigaunt Resistance vs. Antlions vs. the Combine vs. Headcrab Zombies (Antlions and Zombies were rarely in the same place at the same time in the original game, but Episode 2 features a particularly epic brawl in an abandoned mine shaft). The Combine use headcrab shells as a weapon against rebel-controlled areas, and at one point the player gets to control a bunch of antlions.
In fact, the very first time Overwatch soldiers show up, they're seen killing zombies that wander out of the Ravenholm mine shaft.
In Opposing Force there are four sides in play (the player and the friendly Marines, the Xen Aliens, the new aliens that have since disappeared from the story and the Black Ops that used to be with the Marines), and with a level editor there could be five (the traditional "enemy" Marines), but without that level editor you never see more than three in the same place at once. The Black Ops and Race X don't fight as much as the Xenians and Marines, but they do indeed so. More noticeable in the final few chapters.
Legendary: The Box revolves around the Council of 98 (which includes the player) vs. the Black Order vs. the Monsters running amok in the world.
The Story Mode in Godzilla Unleashed consists of four sides: Earth Defenders, Global Defense Forces, Aliens, and Mutants. The sides differ on how they deal with the crystals that arrived from a meteorite and start royally screwing up the Earth, sent by the Big Bad Spacegodzilla. The Earth Defenders goes out of its way to destroy the crystals, even though their efforts do cause massive property damage. The Global Defense Forces work to stop the monsters running amok from trampling all the cities, and try to maintain order throughout the course of the game. The Aliens are loyal to the Vortaak, and want to use the crystals to conquer and enslave Earth. The Mutants wish to use the crystals for power and are willing to trample anyone to get it, whether they are monsters, humans, or aliens.
In The Legend of Spyro: A New Beginning, in the level Dante's Freezer, Spyro arrives right when the Ice Soldiers and the apes are in the middle of a war. Neither of them are pleased to see him. They spend a lot of time bombing each other as well as Spyro, which can sometimes mean that the gigantic mass of enemies in front of you that you're sweating over is wiped out in ten seconds by the other side.
Averted in StarCraft... most of the time. Despite the seemingly perfect set-up of Terran vs. Protoss vs. Zerg, each race consists of various factions. Infighting ensues.
In the novels, the Battle of Tarsonis was depicted as one of these (in the game, there were three separate missions for the battle, allowing them to show that each side was around without having a true melee), with Confederates, Sons of Korhal, Protoss, and Zerg beating the crap out of each other. Mostly, though, the various factions were canny enough to sit back and watch when they found two enemies fighting. Mostly.
Another example can be found in Broodwar, when the UED follows Fenix, Raynor and Mengsk to Aiur and not only encounters Fenix' forces there, but also a bunch of Zerg broods that are still around.
The novel Shadow of the Xel'Naga ends up with a three-way fight over a Xel'Naga temple between the Dominion's Alpha Squadron under General Duke, Kerrigan's new Kukulkan Brood, and a protoss battle group. Nobody wins: after taking serious casualties Duke orders the temple nuked. The warhead wakes up a baby Energy Being inside that eats the protoss and zerg and blasts the rest of Duke's warships out of his way as it leaves the planet.
In "Reign of Chaos Night Elf 4", the three factions are Night Elves (player), humans and orcs, and undead and demons.
"Frozen Throne Blood Elf 3" has the Blood Elves (player), humans, and undead. There are a couple points within the mission where the players has to go through the other two factions fighting it out.
Mario Party is in essence a four player free for all (at least in a standard game), but for the minigame at the end of each turn, teams are determined by the color of the space they landed on, leading to basically random and constantly changing 2v2 and 1v3 alliances, as well as free-for-alls if everyone lands on the same color.
In Devil May Cry 4, there are actually three factions: the Player Characters Dante and Nero, the Order of the Sword, and the Demons. When you're in a battle with enemies from both enemy factions, they will occasionally attack each other instead of Dante/Nero if you stand back long enough and watch the carnage. You're given hints about this situation in Mission 9 when two Assault enemies that were introduced in the last mission jump past and ignore Nero to attack the two Bianco Angelos guarding the Order of the Sword HQ, only to be killed effortlessly as part of an introduction for the Alto Angelo enemies and later in Mission 12 when Fortuna comes under attack, and the Savior and it's army of Bianco and Alto Angelos come in to attack the Mephisto army.
In Devil May Cry 3 before it, there was the conflict between Dante, Vergil and Lady, until Arkham de-allied with Vergil and led the Sons of Sparda to work together against him, while Dante Befriended Lady shortly as well.
The final boss battle in Bloodrayne is a 3-way fight between Rayne, the super-powered Nazi Commander, and the Devil.
Eariler in the game prior to the aforementioned final boss battle, there are also 3-way fights between Rayne, the Nazis and various Vampire creatures. And before that we also get Rayne vs the Nazis vs the Daemites.
Halo: Combat Evolved has Humans vs. Covenant vs. Flood vs. Sentinels, and Halo 2 has Humans vs. Covenant Loyalists vs. Covenant Separatists vs. Flood vs. Forerunner Sentinels. In Halo 3, things settle down into a simpler two-way Everybody vs. the Prophet of Truth and his loyalists, with Gravemind and the Flood taking over as the Big Bad guys after Truth is finally killed near the end Serves as an inversion and subversion of the FPS case mentioned above, with the zombies essentially becoming your temporary allies ... and then backstabbing you again, so now you as the player have two enemies, and all alliances have dissolved. As the Arbiter says, "We trade one enemy for another."
Humans and covenant separatists vs covenant loyalists vs forerunner robots.
In Halo4, you can find Covenant Remnant and Prometheans fighting in the first level that they are both in, making it possible for you to mop the floor with whoever's left. The rest of the game subverts this by having the Remnants and Prometheans unite under the command of Didact.
In Phantasy Star Online 2, native mobs of a particular area will often fight against D-Arker enemies (and vice-versa) when they aren't fighting you.
The Item World in Disgaea. In the earliest levels, the "specialists" that you must kill to level up your weapon ignore everything until you attack them, at which point they may counter, but won't attack. Once you get deeper in, however, you see that their "NPC Ally" designation on your map screen isn't just for show, and you may have to pull off some tricky maneuvers to make sure your enemies don't kill them first if they start out too far away.
The game Sins of a Solar Empire has this as its basic structure — a three-way fight between different factions with different abilities (tech, psionics, wormhole manipulation). Also, Sid Meier's Civilization series, the Dominion games, (most 4x games, in fact)...
The RebellionExpansion Pack has the main three factions each split into Loyalists and Rebels with slight differences between the two. Mainly, each of the six factions has their own Titan (unique ginormous warship that dwarfs entire fleets).
Crysis has the USA vs. North Korea vs. Aliens, but only in the expansion game Crysis Warhead. In the original Crysis, the Koreans were killed off. You see Koreans standing around everywhere, frozen solid.
Crysis 2 has a similar dynamic, with the US forces fighting both CELL PM Cs and the Ceph.
One of Samurai Warriors 2's more interesting fights takes place during Hanzo's story, a three-way fight between Hanzo, Kotaro, and Nene (the game's three playable ninjas). Also Kotaro Fuma's Musou Mode in general, where he often doublecrosses his supposed allies and ends up kicking everybody's ass indiscriminately. Then again, he claims to be Chaos... Also, in the first Samurai Warriors, Masamune Date's ENTIRE STORY MODE consists of nothing but him butting in on other generals' conflicts and annihilating both sides without stopping to think overmuch on whose side is right or wrong... or stopping to think at all, for that matter.
A few of the battles in Sengoku Basara also involves this. The second game has one in which Keiji butts in on the Betrayal at Honnouji and ends up in a battle between Nobunaga and Mitsuhide (all for the reason of just saying hi to Nobunaga) and one where characters crash a battle between Kenshin and Shingen. The third has certain campaigns ending with the characters intruding in on the Battle of Sekigahara and wiping out both Ieyasu and Mitsunari's army.
In Iji, the conflict eventually becomes Iji vs. Tasen vs. Komato.
The Final Boss fight of RefleX is a three-way battle between yourself, an alien Humongous Mecha, and two Kamui fighters from the developer's previous game.
The fourth to last mission in Super Robot WarsOriginal Generation 2 takes place in space, just next to a battle between the Einsts and the Shadow Mirrors/Inspectors. Your team arrives to destroy everybody still standing.
In the first two Total War games you could end up in this situation if two or more powers attacked a third at the same time. In later games, this kind of massive free-for-all is only possible in the custom battles, but boy could this make for awesome battles if your computer could handle the weight.
Armored Core is kind of complicated in a way this trope is played. In 2 it was Zio Matrix vs. Emurade vs. Balena, with the LCC later joining with Balena. But it led to some confusion involving a Civil War between Zio on Earth and on Mars and Balena being caught between the now Corrupted Martian government and the Earth Government.
Near the conclusion of Call of Duty: Modern Warfare 2, after General Shepherd's betrayal, the player is caught in a battle between Makarov's men and Shepherd's, though you're encouraged to let them kill each other off.
Trinity and Hilo Monster in Impossible Creatures feature three players in an RTS free-for-all. Also mission 14 of the single-player campaign, between you, the island's caretakers, and The Virus infected creatures.
Several of the battles in Devil Survivor are like this, and frequently let you choose to intervene on one side or another. In one particularly complex example on Day 6, you have to intervene to stop some demon tamers from escaping the barricade in the midst of a fight between several angels and demons. You can choose to fight either the angels, the demons, or both; meanwhile both the angels and demons will try to kill the tamers before you can defeat them and remove them from battle, resulting in a game over.
In Final Fantasy XIII, some Random Encounters will have one group of monsters fighting another group of rival monsters. You can use this to your advantage to take out the stronger group as the weaker ones whittle their health away.
Jedi Academy has several examples in different levels, with the player character being the third party.
One level has Imperial Stormtroopers fighting Noghri assassins, both also hostile to you.
In another, the Disciples release a Godzilla-like mutated Rancor to ravage a city, but it begins eating them just as surely as it will chase you. That doesn't stop the cultists from attacking you while you're trying to run away from the danged thing before it breaks down the wall between you and it and kills everyone on the other side.
Most notably, the final levels have the Jedi and students from Luke Skywalker's academy fighting the Disciples of Ragnos. If you've chosen to play the Dark Side, the Jedi will sense your evil and attack you as well. This leads to a number of different Mêlée à Trois situations.
In the Drak'theron Keep dungeon of World of Warcraft, the Scourge is attacking the Drakkari ice troll-controlled keep. Both sides are hostile to the player. At the Wrathgate battle, the Horde and Alliance put aside their differences to fight the Scourge until Putress launches the New Plague that kills the living and the Undead at the Alliance, Horde and Scourge forces, killing many and starting a war between the Alliance and the Horde. Both factions then invade the Undercity, which Putress' master Varimathras has taken over; the Alliance hopes to reclaim Lordaeron while the Horde wants their city back. As a result, in Icecrown Citadel, the player must fight through soldiers of the opposing faction, and board their faction's gunship to fight off the other side's.
Red Alert 3 has the Allies vs the Soviets vs the Empire of the Rising Sun.
Red Alert 2: Yuri's Revenge has the Allies vs Soviet Union vs Yuri's forces. The Allies and the Soviets allied with each other until Yuri was defeated, then continued to fight against one other, which forced the Soviets to use their own time machine, leading to the events of RA3.
In Kingdom Hearts II it was Sora and his allies vs. Organization XIII vs. Maleficent and her allies, and The Heartless regularly changing sides among the latter two depending on which one is the strongest for the moment.
In the manga adaptation for the same game, it's Hades vs. Pete vs. Auron, with a Bound and Gagged Megara caught up in the middle, Hercules lying unconscious nearby, and Sora and his friends on the side rooting for Auron.
Syphon Filter 1: Logan & Xing vs. Rhoemer's troops vs. Pharcom. The last act of second game has Logan & friends vs. the Agency vs. the NYPD.
Fallout: New Vegas involves an upcoming battle for Hoover Dam (and by between The NCR, Caesar's Legion and Mr. House, with the main character deciding who they want to side with as the Wild Card of the game. Of course, if the players wish, they can even fight for an Independent New Vegas in which they essentially take over Vegas.
It gets even more complicated with DLC, which reveals that Elijah and Ulysses also want to wipe out the three main factions competing in the Mojave. And they fully have the means to do it.
Fallout 3 has the Brotherhood of Steel as the main good faction and the Enclave as the main antagonists, along with several lesser factions fighting with or against the player as well as each other. At the optional Capitol Building, you may get involved in a four-way battle between yourself, the Enclave's troops, the Super Mutants, and the Talon Company Mercs. In another location, there can be a threesome between Outcasts (friendly to the player unless you piss them off), Mutants, and Raiders.
The plot of Final Fantasy VII quickly becomes a three-way battle between Cloud's group, Shinra and Sephiroth.
Prototype starts out as Alex Mercer vs. Blackwatch/US Marines, but shortly thereafter, the Redlight virus and Elizabeth Green hit the scene as well, adding legions of viral mutants to the fray as well. Later on, Green is killed and her virus starts to die off as well, but the Supreme Hunter takes her place as the third party, although not until the Final Boss fight.
The uncut Ace Combat 3: Electrosphere eventually had four sides fighting each other in every one of its Multiple Endings: UPEO vs. General Resource vs. Neucom vs. Ouroboros. In fact, each ending was mainly characterized by who your character was fighting for in the end (Ouroboros technically got two).
Ace Combat 5 had the setup of Yuktobania vs. Osea vs. Belka in the last few missions. Also, your own squadron had to fight all of them at once until the truth about the third participant went public.
Assassin's Creed: Revelations has this, between the Ottoman guard, the Byzantine Templars and their guards, and the Assassins. It's not uncommon to see both of the opposing factions fighting (or sometimes cause it by forcing them to meet somewhere).
Saints Row often has the player fighting off both rival gangs and police. Nowhere is this more evident than Saints Row The Third's penultimate mission, "Three Way", where the city of Steelport breaks out into chaos as the Luchadores and STAG engage each other in mass warfare, and the Saints have to clean up the mess...by killing off both sides at the worst areas of fighting, along with any extras that show up due to maxed notoriety for both sides.
By the third game in the series, the conflict in Gears of War has the remains of humanity, the Locust, and the Lambent locked in a three way war.
Pit vs Dark Pit vs Underworld Forces in Chapter 6.
Pit vs Space Pirates vs Underworld Forces in Chapter 8.
The big one, starting in Chapter 11, is Palutena's Army vs Hades' Underworld Forces vs Viridi's Forces of Nature.
And then you throw the Aurum and later the Chaos Kin into the mix... Does anybody get along in this game? As a matter of fact, if you stop to pay attention, you will see mooks of different factions beating each other up. Sometimes they'll even kill each other for you so you don't have to.
Actually subverted in the Aurum's case, since Palutena's Army, Hades' Underworld Forces, and Viridi's Forces of Nature join together in defeating them. Played straight with the Chaos Kin, however, as there it's Hades' Underworld Forces, Palutena's Army (under control of the Chaos Kin), and Viridi's Forces of Nature, with Pit siding with the last since they're the most decent group left.
In Sniper Elite, you are an American OSS agent/Cold Sniper dropped into the middle of the Battle Of Berlin. You can come across Germans and Russians fighting each other, and can join in whenever you like or simply observe until one side destroys the other.
End Of Nations the player chooses to side with either the Liberation Front, and the Shadow Revolution, as they fight the Order of Nations and each other.
In Driver's final mission, The President's Run, both the NYPD and the Mafia are all over Tanner like fire ants.
Metroid Prime 2: Echoes has, in progressing order, Luminoth vs Ing vs Robots, Federation Marines vs Space Pirates vs Ing then Robots vs Ing vs Pirates vs Dark Samus vs Samus.
Happens in almost every game of the Total War series, with multiple nations fighting it out in campaign mode.
In the second mission of Perfect Dark Zero, you can trigger a three-way battle between yourself, Killian's gang members, and Datadyne's personnel.
Happens on two separate occasions in the Jak and Daxter series. The first one happens in Jak II: Renegade, which focuses on the three-way struggle between the Underground Resistance, Baron Praxis and the KG, and the Metal Heads. Then, in Jak 3: Wastelander, Haven City becomes a war zone between the resurgent Metal Heads, the Freedom League, and the army of KG robots led by a cybernetically-revived Erol, and that's not even bringing Spargus or the Dark Makers into the mix.
The story of Heroes of Might and Magic: A Strategic Quest is that three sides are battling it over who'll become ruler of Enroth when a noble stumbles through a portal from another world and starts a fourth faction with the same goal.
Happens twice in Max Payne 3: First in chapter 3, where Max and Raul's meeting with the Comando Sombra is rudely interrupted by the Cracha Preto, and second in chapter 9 where the UFE stick their heads into the same.
Marvel Ultimate Alliance 2: The fight in prison 42 soon explodes in a three way battle against the Pro-SRA heroes, the Anti-SRA heroes, and the nano machine controlled super villains.
If the player character decides to create his own faction, it can even become a Mêlée A Quatre.
The Star Wars: Empire at War expansion Forces of Corruption has the Galactic Empire, the Rebel Alliance, and the Zann Consortium duking it out, culminating in a massive final battle over Kuat, in which Zann at first allies with the Rebels only to betray them once he has control over the Super Star Destroyer Eclipse and its One-Hit Kill laser. At that point, it's a straight-up three-way fight.
At one point in Sly 2: Band Of Thieves, there is a three-way battle between the Cooper Gang, Neyla and the Contessa, the latter of whom has Carmelita Fox captured.
The Flash video series Super Mario Bros. Z pits the Mario team (Consisting of Mario, Luigi, Yoshi, Sonic and Shadow) against the Koopa Bros (From Paper Mario) and the Axem Rangers X (Upgraded versions of the Axem Rangers from Super Mario RPG), in a fierce battle on Yoshi's Island. Later, Mecha Sonic appears, who fights against all three, though only one team at a time. He enters the battle by ramming into the Koopa Bros, taking them out instantly. With them down, he then proceeds to nab the Axem Ranger's Chaos Emerald and destroy their gunship. The Rangers attack him, but he systematically beats and then kills them. This leaves only the heroes, Mario, Sonic and the gang, to take on Mecha Sonic, and the rest of the episode revolves around this fight rather than the earlier Mêlée à Trois.
The entire Forever War in PlanetSide is a Mêlée à Trois - Three empires in constant warfare over some tiny rock god-knows-where. Often, three empires will fight over the same base, usually with one team already holding the base and trying to stave off the other two empires (who are busy shooting each other and the defenders at the same time). The areas between bases often turn into deadlocks between two empires until the third empire barges in for some kills.
During the "Stormbreaker Saga" from Sluggy Freelance, a straightforward battle between the kingdoms of Trent and Mercia is interrupted by K'Z'K attacking both sides with its demon army. Whether any of the Trents or Mercians join sides (besides Torg and Zoe) is unclear.
The enemy of my enemy is my enemy's enemy. No more, no less.
In Girl Genius, you have Agatha and her friends, Baron Wulfenbach and his army (with Gilgamesh torn between the two), House Sturmvoraus (with, again, Tarvek being dubious allegiance), Castle Heterodyne, Zola and the conspiracy backing her, The Other and her minions, Othar Tryggvassen (Gentleman Adventurer), the Jägermonsters, and... hu... probably many others, including any power-hungry Spark that would get involved. It doesn't simplify things that The Other, Lucrezia, is currently inhabiting Agatha's body. Honestly, it's more of a Mêlée à Trente-Six.
The best illustration of a Mêlée à Trois, though, would certainly be this page.
In the current arc there's at least seven different factions fighting for control of Mechanicsburg, and word is more are on their way.
In the web comics of Urban Rivals, the B team have to protect their captured leaders from Zlatars robot ninjas, and the Ghiest clan.
The Order of the Stick: This briefly occurs during the Battle of Azure City, when both one of Xykon's decoys and some ninja assassins sent by Daimyo Kubota try to kill Hinjo. Humorously, the duplicate and one of the ninjas actually argue over who gets the kill, before Hinjo suggests a third option:
Occurs in Survival of the Fittest on a couple of occasions. For example, Andrew Klock vs. Xian Chun vs. Cole Hudson (becoming Xian and Cole vs. Andrew) and Maxie Dasai vs. Johnathan Rizzolo vs. Emma Babineaux (and turning into Maxie vs. Riz and Emma).
This is going on throughout the Whateley Universe story "Saks and Violence" but the final battle in the wrecking yard is Jadis (the protagonist) and her fellow Bad Seeds plus as many minions as she could hire on short notice vs. the Empire City Guard and the Cadet Crusaders vs. the armies of the Anti-Champion. Plus whatever Jobe is up to, and the general untrustworthiness of anyone whose last name is Wilkins.
Happens sometimes in Epic Rap Battles of History with third person dropping by to smack both contenstants. Abraham Lincoln interrupted Barack Obama's and Mitt Romney's battle this way. Extragerrated in Rasputin vs Stalin which was first interrupted by Lenin, then by Gorbaczow and then by Putin, each dissing out all previous constentants.
In "The Chase", Azula vs. Aang vs. Zuko. Then one by one the rest of the Gaang shows up, as does Iroh. Eventually collapses into everyone vs. Azula by silent agreement that they all hate her the most. She "surrenders" but gets away anyway.
Arguably, this is also present in the rest of the series as a sort of Right Hand Versus Left Hand between Zuko and the rest of the Fire Nation (especially Zhao) fighting over Aang, while Aang is trying to avoid capture.
An earlier episode had a three-way battle between the Gaang, the Fire Nation, and pirates.
Gang lords auction on a disc with the key to New York. This leads to a battle between Spidey, Hammerhead, Silver Sable, Rhino, and Roderick Kingsley, the guy who actually bought the disc. The winner of the fight? Norman Osborn, who sold Kingsley a fake disc knowing it would never survive the ensuing chaos, and now has all the money Kingsley gave him and the real disc.
Also, the brawl between Tombstone, Doc Ock and Silvermane in "Gangland" with Spidey watching from the side, only getting involved to prevent collateral damage. The villains form a (very) brief alliance to take him down, but Tombstone turns on then to maintain his image, as he couldn't be seen in public siding with the bad guys. The winner? Norman Osborn again as his main rivals were arrested, or in the case of Tombstone had their assets severely crippled.
After the Foot Clan got taken down a few notches in Teenage Mutant Ninja Turtles (2003), New York became a battleground between what was left of the Foot, the mob, and the Purple Dragons gang.
The second season of Transformers Animated is Autobots vs. the Decepticons still working with Megatron vs. Starscream and his clones, with lone enemies like Swindle, Blackarachnia, and Meltdown showing up occasionally.
In the episode "Flirting with Disasters", it was Danny vs. Valerie vs. Technus. Danny's prime target is Technus, though he has to shake Valerie off without hurting her. Valerie primary aims for Danny, though being a ghost hunter, she would eventually have aimed for Technus. Technus concentrated more on world dominating, but he would have warded off both of them as he attempted throughout the episode.
Also, briefly, Danny vs. Vlad vs. Valerie in "Reign Storm" before they all decided to team up against a bigger foe.
In one episode of Kim Possible, Shego, Monkeyfist and Duff Killigan all fight each other for possession of Ron's naked mole rat Rufus. Added awesomeness here as they fight on, in and around the Eiffel Tower, with Kim intervening to save Rufus from harm.
In the Teen Titans episode "Winner Take All", the final battle among friendly competitors is between Robin, Speedy, and Wildebeest. The competitors hold no grudges and are only playing to win the tournament. The fight becomes a one-on-one once Wildebeest loses.
In the Young Justice episode "Drop Zone", on the Team's first mission, they find themselves going up against Bane and the cult organization Kobra, who are also warring against each other.
The Yugoslav Wars were a three-way melee between the Serbs (Eastern Orthdox, backed by the Russians, Greeks and other East Europeans), the Croats (Catholic, backed by Western Europeans) and the Bosnians (mostly Muslim, backed by Arabs and other Muslims). Various alliances were formed and many backs were stabbed in the course of the four-year war.
There were many alliances forged, however. You see, Italians weren't really happy with NDH (they didn't even allow NDH forces to cross to south part of the state), partisans were fighting against any occupators for communist, and Chetniks for royalist Yugoslavia, while Germans simply wanted resources from NDH. So Italians often protected Chetniks and Partisans from NDH, and fought them at other times; Chetniks made alliances with Axis forces against Partisans as well with Partisans against Axis; Germans and Ustashi fought Partisans constantly, but sometimes allied with Chetniks against them...
The Crusades: Roman Catholics vs. Orthodox Christians vs. Muslims.
And members of all three sides taking the opportunity to attack rivals within their own faction — occasionally with the help of members of another faction.
It got more complicated with the Ninth Crusade (1271-1272). Abaqa Khan, the monarch of the Ilkhanate, allied with the Crusaders against the Mamluks. He was a Buddhist. On the other hand, the Northern Crusades (or Baltic Crusades) featured various Catholic factions at war with the last remaining Pagan tribes of Northern Europe. Said Catholic factions rivaled each other and did not hesitate to go into open war. For example the long conflict between Poland and the Teutonic Order. Add a number of Orthodox states, mainly Novgorod, getting involved and you have even more complexity than the Middle Eastern Crusades.
The Haitian Revolution: one group wanted to remain loyal to the French Revolution (mostly free blacks, supported by France), one group wanted independence so they could keep things as they were under the monarchy (mostly whites, supported by Britain), and one group wanted independence for a black nation (mostly slaves, supported by Spain). The free blacks won, but when the French Expeditionary Force arrived and started acting like dicks, the free blacks teamed up with the slaves and established an independent Haiti.
In many governments, the power is often divided up into three branches, with the idea being that no one branch can get all of the power because it has to compete with two other branches. Apart from America, many Commonwealth countries like United Kingdom and New Zealand have separation of power where the government is split into 3 branches (parliament, judiciary and executive). Many Commonwealth countries countries in general also have several parties jockeying for position. As just one example, Canada has had everything from Melees A Trois to Melees A Cinq. The Liberal, Conservative and New Democratic Parties have been competing for decades, with various other parties (Social Credit, Reform, Bloc Quebecois, etc.) being elected to Parliament at any given time.
In the old Soviet Union, the Communist Party, the military, and the KGB tended to function as competing political power blocs.
Many smaller countries went into the war nominally allied with one side but with the full intention of seizing land or other perks from the weakened victor, even if that victor was ostensibly an ally.
Several countries backed efforts to establish a southern Slavic state (Yugoslavia) purely because it would weaken the Austro-Hungarian Empire or allow a pretext for war.
The "Young Turks" allied with Germany, bringing the Ottoman Empire with them. They then participated in a covert plan to travel the Middle East, fermenting various nations to call for a 'jihad' against the British Empire. To the Germans, this was a tactical plan to force Britian to either expend troops quelling uprisings, or lose India, the crown jewel of it's empire. The Turks, however, intended to use the holy warcry to found an all-Turk empire of the Middle East. The plan failed on it's very first mission to Afghanistan due to a wide array of tactical and diplomatic blunders, as well as the British keeping hefty bribes flowing to Afghanistan.
It didn't help that the German agents decided to brew schnapps and get drunk in a country where alcohol was unheard of. Intoxicated European provaceteurs flaunting disregard for local religious laws rarely help under-the-table diplomacy.
World War II was arguably one of these, as two separate wars (Japan vs. China in 1937, Germany vs. Poland in 1939) broke out on opposite sides of the globe and eventually merged into a single massive conflict.
Indeed, the Chinese conflict was a straight example. The Japanese came and took over the major cities in the eastern area. In theory, this caused the Communists and the Kuomintang to work together to fight a guerilla war against the Japanese. In practice, the Japanese tried to keep control over the area, while the rebels tried to gain popular support, with all three sides taking pot shots at each other trying to remove the competition.
Ukrainian Resistance fought in the same time against Polish Resistance, German Army and Russian Army.
The vicious nature of the bureaucratic system in Nazi Germany also often resulted in this, especially in the early days of Nazi rule. There was a time when a shooting war between some combination of the S.A, S.S and the Wehrmacht could have been a real possibility, and was a major motivation for the S.S to viciously consolidate power in the late 1930's.
The term "battle royal" refers to a fight in which three or more combatants fight until only one is left standing.
The term was first coined by the Romans to describe gladiatorial fights involving three or more combatants who would fight until one remained standing or alive. Such battles were considered brutal even by Roman standards, such that early Christians such as Clement of Rome and Ignatius actively campaigned against it to no success.
The battle royal was revived in the arena of boxing in 19th century America, appearing on the undercard of boxing matches. Before the abolition of slavery, such matches featured five or six black slaves who fought blindfolded and bare-knuckled until either one was left standing or until two fighters remained, at which point the blindfolds were taken off and the fight continued as a normal bout. The practice of the battle royal continued long after the abolition into the early 20th century, with the fighters being allowed to keep their winnings.
China has the "Romance of the Three Kingdoms" period that was pretty much this trope.
Korea had a similar time period which saw three dynasties battling it out, which were also called The Three Kingdoms.
Basically every war on the North American continent before the 1840s involved Native American tribes that could lead to... complicated allegiances and events.
The French Revolution which saw the French against more or less everyone at some point, even the US (undeclared naval war). The best example would be the Jacobin Republic, which fought against the British, Austrians and Prussians, while fighting their own civil war against both the moderate Federalists/Girondins in the south and the reactionary Vendeans in the west. The Federalists might have been tolerable to the British, the Vendeans were absolutists like the Austrians, and had they ever met they would have shot each other.
The Iraq War was arguably a clash between the US-led coalition, the Shia insurgents, and the Sunni insurgents.
And before that, ABC, NBC, and CBS competed for the attention of the entire nation.
The British Civil War of the 1640s often had the Royalists, Parliamentarians and 'Club Men'. The latter were locals who just thought the other two factions should go and fight over the fate of the country somewhere else.
Even better was the contemporaneous wars in Ireland. It was already complicated — with Catholic Irish (who wanted to be ruled by the Pope), Less Catholic Irish (who wanted the king to treat them better), Nationalist Irish (who wanted independence) and English and Scottish settlers (who trusted each other as little as they trusted the natives). When the civil war broke out in Britain most factions then split along King or Parliament lines as well.
The conflict in Mali has alliances changing at the drop of a hat. Broadly speaking, there are three major factions: the military junta in Bamako who want to rule the country, the secularist Tuareg MNLA, who want an independent secular Tuareg republic in the Azawad, and a collection of allied Islamist groups (most notably Ansar Dine, the flagship Tuareg Islamist movement, Al-Qaeda in the Islamic Maghreb, and an AQIM splinter group called the Movement for Oneness and Jihad in West Africa) who broadly agree on the goal of an Islamic government in the region but differ on technical points and objectives. In early 2012, after the junta took power in Bamako, the MNLA formed an alliance with the Islamists, and the victorious alliance created the Islamic Republic of Azawad in the northeastern half of the country. However, since then the alliance has crumbled, and after the French and ECOWAS began to deploy forces to support the junta and bring down Ansar Dine in January 2013, the MNLA agreed to work with the French to throw the Islamists out.
In the Middle East, there is a cold war currently going on between Saudi Arabia, Iran, and Israel.
The situation in Syria: there's the Assad regime backed by Russia and Iran, the "Free" Syrian Army backed by the Western countries, and then there are the mujahidin aligned with Al Qaeda. While Assad is slowly weakening and the FSA is fraying, the mujahidin has been gaining ground.
The Russian Civil War: While it's often presented as a straight-up Reds vs. Whites, there were actually many other factions, such as the Blacks (anarchists), Greens (local peasant militias, sometimes backed by the Social-Revolutionary party), foreign intervention forces and many local warlords who shifted their allegiance as it suited them.
In early days of First Indochina War, there were not only fights between French army and Viet Minh, but also skirmish between French and Chinese. To make the whole thing even more complicate, the whole thing, early during the First Indochina War, French were helped by Japaneseremnants.
The Jidai Geki period. There was a reason why the era is often referred to as "The Age of the Country At War". At some point, every major power in Japan had a battle with someone else and alliances were very shaky indeed.