Bleach's new filler arc consists of the Gotei 13 fighting against their clones, yes, it is just THAT awesome.
Due to its Fantasy Kitchen Sink nature, Mahou Sensei Negima! has had Ninja vs. Mage, Mage vs. Demon, Mage vs. Samurai, Mage vs. Vampire, Vampire vs. Samurai, Vampire vs. Martial Artist, Vampire vs. Demon, Mage vs. Swordsman... well, you get the idea. And then the time travel, teleportation, petrification, plant control, and summoning come into play...
The end of Seto no Hanayome features a massive brawl involving mermaid Yakuza, songs of mass destruction, gigantic eels, and the Terminator himself—in a Sailor Fuku—firing laser beams out of his eyes while flexing while stuff continues to explode in the background.
Grenadier: it opens with samurai vs. riflemen, and just the first episode also includes riflemen and machine guns against one six-shot revolver plus Improbable Aiming Skills. It goes from there: revolver vs. magical weapon, revolver vs. super-weapon, revolver vs. magical lance, ...
Kore wa Zombie desu ka? has Vampire Ninja vs Zombie, Magical Girl Uh guy/Zombie, Vampire Ninja and Necromancer vs Vampire Ninja Magical Girl Megalo person.
Marvel and DC often do this, especially with Dracula since there is no more copyright law applicable. Batman seems to be a regular feature of this sort of thing, fighting Judge Dredd, Aliens, and Predators semi regularly.
Not to mention Batman and Superman Vs. Vampires and Werewolves.
Superman and Batman vs Aliens and Predator.
Aliens have fought: Batman, Superman, Green Lantern, Judge Dredd, Wildcats. Predators have fought Batman, Superman, Magnus Robot Fighter, Judge Dredd, The JLA and Tarzan. That's not even counting two Witchblade, Darkness, Aliens and Predator 4-ways, one of which was better than the other.
There's a mini-arc of Gold Digger in which a princess and her spec ops team pilot an ersatzVoltron against a group of pirates and their Gaogaigar lookalike. The fight lasts three issues and includes triple-wielded katanas, evil twins, and a guitar riff that can stop time. Did I mention that all of the characters involved are leprechauns?
Batgirl: (While being strangled by Dracula) "Hopefully you won't hold this against me." Supergirl:That's what she said. Batgirl:You're funny. Supergirl:I try.
Deadpool's most recent comics have tended towards this, especially since he teamed up with his own zombie-universe severed head to fight dinosaurs, some of which become zombies, and then later are infected by the Venom symbiote. He also helped a superhero trucker fight alien raccoons, and helped Hercules solve a labyrinth created by Arcade, who was hired by a demon.
Marvel's various "Thor vs. Hercules" miniseries, one of which included the two of them disguised as one another.
The entirety of Nextwave can be described thus. Crazy AwesomeSupers and their even more crazy awesome robot-supremacist robot fighting Pantsless Kaiju, Samurai Robots, Cannibal Drop Bears, laser eyebeam-shooting Stephen Hawking clones and much much more!
The comic book Zombies vs. Robots and its sequel Zombies vs. Robots vs. Amazons.
Lucio Fulci's Zombi 2 features the ultimate underwater battle... zombie versus shark! The undeath-or-death duel ends in a draw: the zombie's missing an arm, but the wounded tiger shark swims away, where he presumably goes Up to Eleven by becoming an offscreen zombie shark.
Pathfinder: Native Americans vs. Vikings. Bonus points for having actually happened in Real Life — the Vikings reached America almost five hundred years before Columbus, and even tried to colonize Newfoundland, but were driven out by the natives.
A hundred points to wizard Harry Dresden, for riding out on the back of a zombie T-Rex to face off against necromancers and their zombie armies at the climax of Dead Beat.
Plus several million for riding out on said T-Rex to the jaunty tune of polka.
Plus additional points for using a loophole in the series' rules against using necromancy. The Fifth Law of Magic prohibits raising the dead, but as Harry points out (to two people who could legally cut off his head for breaking said Law): "That only applies to raising HUMAN dead."
Further points because the specific skeleton is, in fact, Sue, aka the most complete T-rex skeleton so far found.
And sixty-five million bonus points for exploiting how necromantic zombies' power increases in proportion to how long they've been dead.
Along with a zombie T-Rex, Dead Beat also features ninja ghoul versus valkyrie security consultant.
Sticks and stones may break your bones, but Chinese throwing stars get you a dozen stitches.
Changes has an epic battle of Cool Versus Awesome. Involves three vampires, The Fair Folk, a Knight of the Cross or three, dozens of wizards (including the new Winter Knight and the Blackstaff), a Chinese guardian spirit, an entire army of Japanese kenku ninja-spirits, and Odin versus the entire Red Court of vampires, including the Red King, armies of half-vampire acolytes, and the Lords of the Outer Night, more or less Mayincatec gods, and South American mercenaries.
In fact, this trope is arguably the entire reason for the series' existence, and Great Furies does it work out well.
You can take the page picture, replace the gladiator with a Roman legionary, and you've essentially summed the middle two books of the series.
In Complete World Knowledge, details of the historic feud between submariners and zeppeliners are given. In a subversion, the author describes this as "the most pointless feud in human history".
Gandalf versus the Balrog in The Lord of the Rings, in what is literally a battle of two angels, one of whom is fallen.
Two of the books in the Skulduggery Pleasant series, Playing With Fire and The Faceless Ones, feature a detective skeleton wizard and his companions versus near immortal gods. The wizards win the first time. They at least manage to survive the attack (mostly) by the multiple fully powered gods in the next book.
Although they did skirt the obvious by having the pirate fight a knight and the ninja fight a Spartan, likely to avoid trolling.
The guy who programs the simulations actually said that they were avoiding it because no one would agree on the right way to test it, and no one on the losing side would accept the result anyway.
A similar concept was used a couple of times on the teen show, Dude, What Would Happen?, albeit with cheap prop duels rather than computer simulations. Once they even did "Vikings vs. Pirates", which is Did Not Do the Research, as "viking" was basically just Old Norse for "pirate".
Top Gear delights in pitting one Cool Car against another, but it has also featured Cool Car v. Cool Boat (Ferrari Daytona v. a brand new carbon-fiber superboat) and Cool Car v. Cool Plane (Bugatti Veyron v. RAF Eurofighter Typhoon.
The original Dungeon Master's Guide included rules for running crossover battles between D&D heroes and characters from other early TSR games, including Boot Hill (Wild West gunslingers) and Gamma World (post-apocalyptic mutants).
Feng Shui features this a lot, given its timehopping Secret War setting. Shaolin monks battle evil cyborg demons from the future, transformed animals fight evil sorcerers that can turn them back into their regular animal form, maverick cops and heroic triad gangsters fight intelligent cyborg apes and their minions who like to BLOW THINGS UP. And that's just for starters.
As one person said, "Exalted is robots versus dinosaurs!" More aptly, it's glorious golden demigods and keepers of the earth, shapeshifting social engineers, a magically-empowered martial dynastic empire and fate's ninjas versus the undead servants of oblivion, mad fairies from beyond reality, demon-kings who gain power from acting like B-movie villains, Communist cyborg soldiers from another dimension, and each other.
Upcoming AEG game Smash-Up is built on this trope. Players choose two "factions" from eight - including Pirates, Ninjas, Dinosaurs, Wizards, Robots, Zombies, Aliens, and Tricksters - to build a deck out of and go up against decks of two others.
Video Games
As a general rule, Fighting Games exist to allow all sorts of martial arts around the world to duke it out virtually.
The Command & Conquer series have lots and lots of this, particularly when you get tier 3 you can start to pump out really awesome stuff like dual barreled tanks with rocket launchers, alien tripods with EMP and triple lasers and stealth robots armed with dual lasers and flamethrowers.
The spin-off Red Alert series takes the Rule Of Cool and turns it Up to Eleven. Actual battlefield scenario: mortar-equipped hovercraft are launching parachute-equipped cyber-bears while getting shot at by dolphins whose sonar has been weaponized; the bears' mission is to take out a giant mecha factory before they get gunned down by a immensely-psychically-powerful Japanese schoolgirl who is being backed up by fellow young ladies in rocket packs. While on the other side of the map, amphibious destroyers are getting nailed by tesla coils and tanks the size of city blocks. Yes.
Plants Vs Zombies is about defending your house from zombies by planting cute plants. The awesomeness of the zombies rises as you progress through the game.
And for ultra awesomeness, the final boss battle is a freakin' huge robot piloted by a zombie scientist that only half of fits on the screen. On your ROOFTOP.
Scribblenauts allows you to pit nearly everything that's cool against nearly everything that's awesome.
Guilty Gear and BlazBlue. The former has pirates (in a raincoat or sailor-fuku), police (that're dressed in something like priest clothes), assassins, an American Ninja and a whole lot more. The latter has what is essentially the Joker as a Smooth Criminal, cat-people, cyborgs, vampires, a Mad Scientist and more.
Kongai, a superbly balanced online card game about battles involving Samurai, Ninja, Hot Amazons, Vampires, a Barbarian Tribe, Pirates, Knights, Robots and Witches.
Skyrim's plot basically boils down to Vikings vs. Romans vs. dragons. There's also a bit of Ancient Egypt in there in the form of the draugr. What's not to like?
The player can become a vampire or a werewolf too!
The draugr are actually Nordic zombies that were said to retain some intelligence and were almost invicible. Thanks history channel and specials about zombies.
Saints Row 2 has a minigame where you're a Cop on a reality TV show, and you have to stop randomly generated crimes. One of them is to "Stop the Fight of the Century," which when you arrive at the checkpoint, you find out is a gang of pirates fighting a gang of ninjas.
"Attention all cars, this is dispatch, we have Pirates vs Ninjas, repeat, Pirates vs Ninjas."
Related: "Chainsaws are standard issue for cops, right? Go "catch" that purse-snatcher!"
Now we have Ultimate Marvel Vs Capcom 3, with B.O.W.s and Lawyers oh my!
Street Fighter X Tekken is the latest installment so far which allows you play as fighters of the two series as well as an electric superhero, two anime cats, a robot, and Pac-Man with a wooden robot.
Ogre Battle has ninjas, vampires, werewolves, knights, amazons, valkyries, wizards, witches, so on and so on.
In Prototype, when the Badass NormalSpecialist Cross takes on Alex Mercer, the one responsible for killing entire platoons of Marines and capable of taking out Heavy Armor, man on man (Well, until Blackwatch send reinforcements in the form of SpecOps Soldiers). The end result is basically a tie (Mercer is incapacitated by Cross, but escapes when Cross turns away to use his radio to call for an Extraction Helicopter).
Touhou: Take your pick: Shrine Maiden versus Vampires, Ninja Maid versus half-ghost samurai gardener, vaguely-lesbian Witches versus Immortal Aliens, Dumbass Fairy versus The Judge of The Dead, Shrine Maiden versus Gods, Witch allied with Mad Scientist versus Nuclear-powered Raven from Hell, Paparazzi versus everyone... explained by Gensoukyou being the last refuge for fantasy.
Kid Icarus: Uprising has a short arc that is essentially Greek(ish) gods versus alien invaders.
Webcomics
The Adventures of Dr. McNinja has had, in no particular order, ninjas and a doctor ninja versus... robots, clowns, a flying bodybuilder, a giant Paul Bunyan who was really a child, evil ninjas, pirates, ghosts, Mexican banditos on dinosaurs, vampires, zombies, a unicorn motorcycle, a ghost wizard, someone pretending to be a robot, ninja zombies, more robots, zombie Benjamin Franklin, Dracula (Dracula also had a robot Dracula), a Danish 80s action movie hero and his ninjas, clone ninjas, ghost wizards, Mayincatec robot temple guards, future dinosaurs from space, a vengeful space ghost that explodes people, a samurai demon, sky pirates, a luchador doctor, and a king on a dirtbike. At any given point, those enemies may have fought each other as well.
Axe Cop has had the title character and his allies (including dinosaurs, people with unicorn horns, a vampire wizard ninja and his brother who's also a werewolf) vs. aliens, vampire half-babies, Humongous Mecha, flying books, Bad Santa...
The Dragon Doctors is about magical doctors of many different disciplines who have banded together, and they've fought against various equally unusual opponents. The docs themselves are a wizard (with healing and shapeshifting magic), a soldier/surgeon, a shaman/therapist, and a Magitek specialist. They've faced off against a horde of assassins, a serial killer who kills dreaming shamans, and Goro (the soldier/surgeon) is currently fending off an all-female Quirky Miniboss Squad consisting of a pistol-wielding shapeshifter, a mage in a ballcap, a female ogre and a lamia with a petrifying ray gun.
The "Ninjas vs. Pirates" wallpaper from the Dan and Mab's Furry Adventures download page is a uniquely Amberish take on the subject. There's actually a funny story behind it...
Saudia Arabia and Somalia's fight in Scandinavia and the World, considering that Somalia is a pirate, and Saudi Arabia is a 'ninja'.
QuestionableContent has Pintsize (the Anthro PC—a PC-bot) steal Faye's panties and pretend he's an Underwear Ninja. Faye responds by sticking a bra 'round her head like a pirate eyepatch, thus becoming, in Pintsize's words, "A Bra Pirate! The nemesis of all Underwear Ninja." Marten's response? To paraphrase, "WTF?"
There are some storylines in Teenage Mutant Ninja Turtles in which they fight alien dinosaurs. Robots and other mutants are also common foes.
An episode of Justice League Unlimited pitted Aquaman against Wonder Twinsexpies. This resulted in a battle in a Downpour-flooded office building, between the Prince of the Sea and Shifter as a swimming tyrannosaurus.
A recent LEGO line called Ninjago pits heroic ninjas (with cool tornado powers in tv spots) against armored skeletons that ride motorcycle-like vehicles.
Many of Samurai Jack's adventures invoke this trope: Samurai vs Viking Rock Monster, Samurai vs Blind Archers, Samurai vs Scotsman Barbarian, etc.
Real Life
Older Than Feudalism: The Battle of Zama. A climactic battle between two of the mightiest empires in history commanded by the two greatest generals of the Sword And Sandal era. On the Carthaginian side is the Magnetic Hero, Hannibal Barca. On the Roman side is the Cincinnatus type Scipio Africanus. Who will win? Rome. To put the Battle of Zama into perspective, you have Roman legions being led by an eccentric general who really should not have this position under normal circumstances versus the aforementioned Magnetic Hero leading a diverse mercenary army and War Elephants. By all accounts it was epic.
Waterloo, with the real-life (And significantly more Badass) Redcoat Army under the Iron Duke Arthur Wellesley up against the Grande Armee under Bona Fide Magnificent Bastard Napoleon Bonaparte (Who also happened to be l'Empereur) in the final battle of the 26-year long French Revolutionary wars.
Tennis rivalries - and sports rivalries in general - pretty much run on this trope. Federer vs. Nadal in the present and Sampras vs. Agassi in the past are examples. The 2007 and 2008 Wimbledon Men Singles Championship matches were noted for featuring two players in their prime fighting tooth and nail for every point.
