So, you've got a character that you want to show is really dangerous. You could give him/her the normal two arms or legs, but that's just not enough. Maybe you could replace one of those arms with a really big gun, or a sword, or have it transform into something else.
If that doesn't work, you can always give a character extra arms... because four arms good, two arms bad, right?
For obvious reasons, normal humans don't get this treatment, because it would look pretty awkward having to do bodily cleaning... and having four arms to go around would be a tailor's nightmare. If you're a mutant or an evil genius, you don't have to worry about this, because Freaky Is Cool.
Multi-Armed and Dangerous characters come in two flavors:
The extra arms are a regular part of the body.
They're made from prosthetics/synthetic materials that are usually attached to the person.
Vice Admiral Onigumo has a Spider Devil's Fruit, whose mastery of it allows use to manifest the extra arms he'd normally get in his hybrid form via his hair, allowing him to use eight swords at once.
During the Thriller Bark story arc, we get a brief glimpse at a zombie general who has four arms, each holding a pistol. Given the nature of the island's zombies, we can presume that these were grafted on by Dr. Hogback. Unfortunately, we never see this zombie again, and can only imagine the badassery that he could have dealt out.
Masashi Kishimoto likes to use this trope in Naruto:
Kidoumaru, one of the Sound Four ninjas has six arms.
Sasori has the Third Kazekage's puppet form equipped with this, ironically being one of the few examples in the series to be caused by a jutsu.
One of Pain's multiple bodies, the Asura Path, has six arms, and on top of that, THREE FACES. Like all the other Paths of Pain, this is actually a reference to Buddhism; the asuras are a type of diety which also have those features.
Hosts of a tailed beast are capable of making limbs out of chakra sprout from their body. Killer Bee makes Combat Tentacles while Naruto eventually learns to make them into many extra limbs that can each make their own Rasengan. This even includes making a pair of tiny hands coming from his finger that form their own tiny Rasenshuriken.
By far and away the most dangerous example of this trope is Madara Uchiha's Susanoo, especially its perfect form. Four arms, two strange blades, and capable of contributing to his techniques through also using hand signs. He cuts a mountain in half with it just to show off!
The above example is topped by, fittingly enough, his archenemy Hashirama Senju. To fight a Nine-Tails sheathed in the above-mentioned Perfect Susanoo, he creates a giant moving Kannon statue, complete with one thousand arms.
One of the one-off characters in Ranma ˝, Rouge, fell into "The Spring of Drowned Asura". Asura is a Hindu god (or demon) with three faces and six arms. Rouge and Pantyhose Taro manage to destroy the Tendō home in a fight over therapeutic magnets.
Tenshinhan used a technique that had him grow two additional arms to fight Goku in the original series. Goku countered by moving his arms so fast it at least looked like he had six.
Inverted in Dragon Ball Z with Caterpy, a giant Caterpillar warrior that "fights" Goku in Otherworld. He lives up to his Multi-Armed status with 10 arms to use for combat. His "Dangerous" side... Not so much.
Nnoitra Gilga, whose released form allows him multiple arms, as well as regeneration powers. Initially he has four arms, and four scythes to go with them. When one of his arms is promptly sliced off by his opponent, the regeneration kicks in and he also ups the arm count to six.
Wonderweiss's release form also lets him grow a bunch of extra arms coming from his shoulders.
In Franken Fran, Fran occasionally affixes as many as four extra arms to her body for particularly delicate procedures; Apparently, turning a mutilated human into a giant caterpillar with a human head is fussy work.
Asura Gundam from G Gundam is an intentional Hindu reference.
The O, personal mobile suit to Big Bad Paptimus Scirocco of Zeta Gundam has a pair of beam saber wielding sub arms in its skirt armor, thus turning the massive Mighty Glacier looking machine into a Lightning Bruiser melee combat monster as it can wield four beam sabers at once with perfect control thanks to its mentally controlled biocomputer. That's because The O was designed by none other than Mamoru Nagano, who is a great fan of this trope.
The Gaplant TR-5 from Advance of Zeta also has skirt-armor subarms, while Gundam Hazel can be equipped with, in addition to the aforementioned skirt-armor subarms, two giant wire-guided rocket arms developed from the Psyco Gundam on its shoulder and wire-guided arm-shield on its forearm.
The Xeku Zwei from Gundam Sentinel has two more sub arms for melee and shooting a giant beam bazooka.
The Neue Ziel from Gundam 0083 has six arms, each capable of generating gigantic beam sabers. UC, usually considered the most "realistic" of the various GundamAlternate Continuities by its devotees, ironically is even more guilty of overdoing with arms than even Gundam 00.
Seravee Gundam from Gundam 00 has four BFGs, two on its shoulders and two in its knees. These all are capable of sprouting hands equipped with beam sabers in addition to the Seravee's normal pair, allowing Seravee to simultaneously fight with six beam sabers at one time. One can see that they really went out of their way to keep Seravee from suffering from its predecessor Gundam Virtue's weakness in close-range combat. That's right: Seravee is a BFG-toting long-range artillery mobile suit with multiple arms wielding multiple beam sabers as back-up weaponry.
The Orphan in the sixth episode of Mai-HiME has, surprise surprise, six arms.
Justice from Afro Samurai has three arms, one of which is kept hidden.
Mamoru Nagano is probably the king of this trope, because if he designs mecha the chances are that they will be multiarmed. In his own series, The Five Star Stories, the biggest, nastiest and most heavily armed mecha of all times, the Jagd Mirage, had not just two like The O, but four deployable sub-arms, which, together with its two additional sub-legs, drove the limb count to ten. These sub-arms could be used to wield swords of guns, but generally were used to manipulate shields (called veils there) to cover the mecha and brace it against the immense recoil of the two truly titanical cannons it carried as its main armament.
One of the teams in The Law of Ueki, which has a military theme, has a guy whose special ability is growing extra arms. To carry more guns. The upgraded form of this ability is even more arms. To shoot even more guns.
In Ultimate Teacher those with invertebrate genes can grow extra arms, depending what genes they were mixed with.
Rengoku in Ninja Scroll: The Series is a shinobi that bears four arms. Additionally, as she's proficient with self-surgery, she has a penchant for removing her own arms and attaching other beings' limbs (animals included) onto her own body to suit her current needs.
Puella Magi Madoka Magica takes this trope to its logical extreme with Patricia: A Witch that's literally just a bundle of 6 arms in a sailor fuku, that forms something like a rudimentary "spider". Look!◊
The orochi-bito from Magic: The Gathering's Kamigawa setting. The Vedalken, a more widespread species, also demonstrate two more arms than other humanoids, at least in some forms - the mutated vedalken of Mirrodin sport four, while Ravnica's and Alara's mostly only have two, with the exception of Vigean Graftmage who at least has the excuse of being a mutant.
Super Munchkin has the "Four-Armed and Forewarned" power, which gives your character two extra Hand Slots for items.
The X-Men villain Spiral has six arms (two of which are cybernetic, presumably replacing real ones lost from injury in a battle that happened before her first appearance); she's also both a sorceress and can fight with a sword in each hand.
In Marvel vs. Capcom 2, the trope title is a nickname for the team of Spiral, Omega Red, and Shuma Gorath.
Furthermore there's henchman types Barbarus and Forearm, who are practically indistinguishable from one another. The former probably directly inspired the latter, though. Marvel likes this trope.
The X-Men 2099 once fought a twisted version of the original five X-Men. The Beast parallel had three arms, two on the right side and one on the left.
In the Earth X trilogy, Hawkeye's mutation from when everyone on Earth gained superpowers was four arms. We only see them in flashback, but he probably gained some ability to Dual Wield bows.
The Spider Doppelganger had multiple, clawed arms.
And let's not forget the venerable Dr. Octopus. And derivatives from his mold like Lady Octopus and the Squid. Though the Squid would probably be upset at the suggestion that he's somehow based on ol' Doc.
In Earth X, there is a woman with six arms that goes by the name of Black Widow (no relation to Natasha Romanoff). She had sporadic appearances within the comic, appearing either in long shots or as part of the background, as well as having no spoken dialogue. An early concept sketch for Venom also showed her with six arms, generated by the symbiote.
Coat Of Arms only has two naturally but her coat gives her two more.
Ai Apaec of the Dark Avengers has about eight limbs, and he could be joined by any other deities from mythology who were examples should Marvel decide to use them.
Stryker from Image Comics' Cyberforce was a mutant born with four arms... three on one side. After an accident resulted in the loss of all three right arms, he was fixed up with cybernetics, once again, for all three. Not only is he a pretty normal guy aside from a slight temper problem, he gleefully uses his three right arms to tripe wield pistols in combat.
Rip Roar, a bad guy from Young Justice. In fact, the original YJ baddie. A wrestler from Apokolips, ol' Rip has four arms and more hair than the floor at Supercuts.
Frank Miller's Ronin features a humanoid four-armed rat ninja that threatens the title character at one point. He loses one arm to the samurai almost instantly, but still puts up a good fight with the remaining three.
A one-shot comic that goes by the name of Chase Variant features a female lead that sports four arms.
General Grievous has arms that can both split in two. He's a cyborg, so it kind of makes sense. In Star Wars: Clone Wars he could hold lightsabers with his feet, too. So theoretically he could use 5 lightsabers at once (one foot would still be needed to stand on).
Obi-Wan's contact Dex had four arms, but this may just avert this trope as he didn't play any part in the main series other than an information source. Star Wars: The Clone Wars (not the same as the previously mentionedClone Wars) introduces another member of the species, Jedi Master Pong Krell, who "merely" dual-wielded double-sided lightsabers, but did do a four-way Force shove.
The Thisspiasians, who have four arms and no legs (they slither along on the ground instead). They, however, prefer to keep their two lower arms hidden in public.
Maybe not as dangerous, but used as a surprise: Zaphod tags Arthur with a surprise lower left (or is it centre?) in the movie version of The Hitchhiker's Guide to the Galaxy. According to the novel, Zaphod had the extra arm fitted to improve his ski-boxing.
The Golden Voyage of Sinbad. A statue of the Hindu goddess Kali is animated, "grows" a sword out of each palm of her six hands and fights Sinbad and his crew.
Six-Shooter in the Puppet Master movies is a cowboy puppet with six arms and as many little revolvers.
During the final chase sequence in Terminator 2, the T-1000 can briefly be seen operating the helicopter's controls with two arms while reloading and firing his submachinegun with another two.
One of the assassins in Ćon Flux (based on the animated show as well) has hands instead of feet.
The Kraken from Clash of the Titans. In the 1981 version it had four arms, in the 2010 version it had two arms and two tentacles.
Several Kaiju (Trespasser, Scunner, Knifehead) in Pacific Rim have four arms. The Chinese Jaeger Crimson Typhoon has three arms.
Men In Black 3 features a four-armed alien thug at a bowling alley who pulls four guns on Agent K. Subverted because K makes short work of him anyway.
Both MUTOs possess eight limbs total: the female has four forelegs, two hind legs, and a set of smaller arms, while the male MUTO has two forelegs, two hind legs, a pair of enormous wings, and a set of smaller arms.
The Teaser Trailer Monster has several arms with hooked claws.
Visser Three from Animorphs morphs into a vaguely-described creature like this in The Threat. All that's really known about it is that it is "dark and large and has more arms than it should".
Quadrus "Quad" Dominus from Duumvirate starts carrying a gun for each of his four hands after a brush with death. He's six at the time.
The "Moties" from Larry Niven and Jerry Pournelle's The Mote in God's Eye have asymmetric limbs — two small arms on the right, and one massive arm (the "gripping hand") on the left. (This is thought to be a result of having their genes cluttered with millions of years of mutations from the endless cycles of nuclear wars caused by their biological need for constant pregnancy. The latent genes for four limbs are still present, as the Warrior and Watchmaker castes still show.) Which allows arguing nerds to use the phrase "on the gripping hand" where normal people might say "but on the other hand", realize they want to go on to present a third option, and be at a loss for how to do it. Sweet.
The Drummer from Wild Cards. His multiple arms aren't exactly combat-specific, but he can use them that way quite effectively.
The green Barsoomians are four-armed killing machines fourteen feet tall. They love to quadruple-wield BFSes as well.
The White Apes of those stories also had four arms.
Technically speaking, both species have two arms, two legs, and two "intermediate limbs" that can be used as both.
The Wreed from Calculating God have arms in front and back as well as two on either side. They escape the "two eyes" problem by having a single optical strip that runs around their entire "head". They suffer from multiple cognitive deficits as a (dubious) result, though.
The Hitchhiker's Guide to the Galaxy: Zaphod Beeblebrox has three arms. He wasn't born that way; he got the third one added on to help with his "ski-boxing". And according to And Another Thing..., this may actually be so he has one hand for each of Eccentrica Gallumbits' breasts. Though it's not clear entirely.
The Shrike from Hyperion is a 3-meter tall, 4-armed, time-manipulating killing machine (literally) covered in spikes. Granted, having 4 arms instead of 2 doesn't make it much more dangerous than it would already be, as it can stop time and wipe out entire armies.
The Chaos creature Skarhaddoth from Hammer of Daemons has four arms. In his first appearance he wields two meat cleavers along with two shields, and in his second he uses four scimitars. There are other multi-armed Chaos beasties stalking Draakasi. Dark Adeptus has various Techpriests with mechadendrites running around.
In For the Emperor, there is a plot point related to this trope. A tau ambassador is assassinated in the middle of a party and no-one can see who the shooter was, especially when everyone draws weapons in the ensuing confusion. It turns out to be the person who seemed one of the least likely, Governor Grice, because he's secretly a tyranid mutant and his shapeless clothes hide not a flabby body but an extra arm easily capable of coming out to fire a gun and withdrawing back, leaving his other two hands innocently empty.
The indigenous aliens of Marduk, in David Weber's Prince Roger series, had four arms, which along with being huge, allowed them to carry BFGs that the humans had used on their now-defunct power armor.
The warrior drone cho-ja in Janny Wurt's Empire trilogy. Their multiple arms also end in blades.
The title character of Mikhail Akhmanov's Dick Simon novels was born in a human town on planet Tayahat whose gravity is 1.5 Earth norm. The planet is populated by a tribal race of four-armed humanoids. Their males live for combat, and boys are trained from young age to kill (as well as honor). Dick is brought to them as a boy by his father and is raised as one of them, before leaving to join the Academy, where he receives more modern training as an operative by a red-headed Texan.
In a bizarrely non-fantastic example, Flint Murtaugh from Robert McCammon's Gone South is a bounty hunter with three arms: his own, and the single undersized limb of his parasitic twin, Clint. Clint is near-mindless, blind, and embedded in Flint's torso, yet has been trained by his brother to point a small pistol as a hold-out surprise. Subverted in that Clint can't aim or fire it properly, but Flint's quarry seldom realizes this.
This is one of the key plot points in the Tipping Point Trilogy , by Alan Dean Foster. Bodily manipulation is as easy as getting new custom-fitted clothing, and is often used to add extra limbs. Note that these are not necessarily weapons, or designed explicitly to carry weapons; for instance, a waiter may get an extra set of arms to improve carrying capacity.
In the Vorkosigan Saga, the Quaddies are so named because they have four arms and no legs (they are genetically designed freefall dwellers.) Miles notes at one point how unfair it is that their troops can literally shoot and reload at the same time.
When Piper and Leo got possessed by a couple of Hindu gods in one episode of Charmed, Piper grew four more arms.
In the fourth season episode "The Way" of Xena: Warrior Princess, Xena and Gabrielle are confronted by a demonic sorcerer named Indrajit while in India. After Xena slices off one of Indrajit's arms, it grows back and is soon joined by four more. Now a six-armed warrior, Indrajit proceeds to prove his badassery by slicing both of Xena's arms off. But wait, there's more! Xena, literally disarmed at this point, calls upon the Hindu god Krishna to help her. He transforms her into an avatar of Kali Freaky Is Cool. Needless to say, if you thought Xena was wicked before, think about how dangerous she is once she becomes a four-armed goddess of death. Indrajit, surprise surprise, is no longer with us. When the battle is over, she is restored to normal.
Monty Python's Flying Circus. One of Terry Gilliam's animations had a mugger saying "Hands up!" to a victim. The victim puts his hands up — and then another pair of hands (and arms), and another... then slams all of his hands on the mugger's head.
Neil of The Young Ones was temporarily granted six pairs of hands by an unseen genie, but the genie was killed and the extra arms vanished before he could use his new appendages, or even show them to his housemates.
Although we never see them, the Venusians who invented the type of aikido practiced by some versions of Doctor Who are said to have five arms and five legs, which make its various maneuvers a lot more effective.
Myths & Religion
Almost all Hindu deities, but probably most notably Kali◊. Hindu deities are only depicted as having multiple limbs to show their divinity and ability to do multiple things at the same time. Depending on the intent of the depiction, you can find representations of the Hindu gods with the standard 2 arms and 2 legs, rather than the typically thought of 6 arms, 2 legs.
The Bodhisattva Avalokitesvara is often depicted with a thousand arms.
Older Than Feudalism: The three Hekatonkheir brothers in Hesiod's Theogony were massive giants (or perhaps deities) who embodied nautral disasters, born with a hundred arms and fifty heads each. Thankfully they were on the Greek God's side and greatly helped them in the battle against the Titans by throwing one hundred mountains a piece at once at the immortal enemies.
Norse Mythology: As told in The Saga of Hervor and Heidrek, the giant Starkad Aludreng (grandfather of the more famous Starkad the Old) had eight arms, and wielded four swords at once in combat. He was eventually killed by Thor for abducting princess Alfhild of Alfheim.
SCP Foundation, SCP-1788 ("The Adults"). Adult forms of SCP-1788 appear to be extremely obese human beings with two extra arms located below their main ones. Their bones are reinforced with heavy metals and their muscles have been interwoven with carbon nanotubes, giving them superhuman strength, speed and durability.
Sahuagin are a race of evil fishmen. The normal ones are dangerous enough, but some of them also sprout an extra set of arms.
Thri-Kreen ("mantis warriors") — badass race of social mantis-hoppers living in arid lands, abundant in (but not limited to) Athas, the Dark Sun setting. Has inheritance memory, poisonous bite, low water requirement, hard exoskeleton, derives construction material from saliva, jumps like grasshopper, throws big shurikens... and can wield small or medium weapons in each of four hands.
Dark Sun setting: B'rohg (tall humanoid giants with 4 arms that are formidable opponents), Feylaar (an ape-like Neutral Evil monster with four powerful arms).
Second and third edition have the Modrons, Outsiders and embodiments of Law and Order who had geometric shapes based on their caste, and a number of limbs equal to that caste. Tridrones, Quadrones and Pentadrones, the most intelligent of the "base" Modrons, have three, four and five arms respectively (as well as an equal number of legs).
Additional 1st Edition modrons with multiple limbs: septon (7 arms), hexton (2 arms and 4 tentacles) and quinton (5 arms).
Dungeon Master's Guide 2 for 3.5e had the Abberant-Limbed trait, which allowed one to gain either an extra pair of arms, or an extra pair of legs. Either way, it added a couple of level adjustments. Other options included the Insectile Creature Template from Savage Species , Arachnoid Creature Template from Underdark (didn't apply to Humanoids, but see Template stacking...) and a web enhancement for customising the Half-Fiend Template.
The Known World setting of Basic D&D (and the Mystara setting of AD&D) have the Bone (Skeletal) Golem. It has four arms, all capable of wielding weapons.
The Greyhawk setting deity Hextor has six arms, with two hands holding shields and four holding weapons.
Module S1 Tomb of Horrors had a mutated four armed gargoyle that attacked anyone entering its room.
The White Wolf supplement Creature Collection III: Savage Bestiary had the multi-armed template, which could be applied to... well, anything, so long as it has arms. This includes your character.
There were enough of these in 3.5 that they had their own feats: Multiattack (allowing a monster to use all of his arms with less of a penalty) and Multi-Weapon Fighting (like Two-Weapon Fighting, but for more than two weapons).
3rd Edition Creature Collection supplement. The Narleth was a half-human/half-spider monster with four arms ending in strong, clawed hands.
A number of deities and related creatures in the 1E AD&D Deities & Demigods Cyclopedia had multiple arms.
Babylonian mythos: Druaga (8 arms)
Chinese mythos: Lu Yueh (6 arms), Ma Yuan (8 arms), No Cha (8 arms), Tou Mu (16 arms)
Egyptian mythos: Anhur will sometimes take forms with more than 2 arms.
Greek mythos: Hecatoncheire (100 arms)
Hindu mythos: Agni (7 arms), Kali (4 arms), Karttikeya (12 arms), Surya (4 arms), Vishnu (4 arms).
Melnibonean mythos: Mist Giant (4 arms).
Additional deity-related creatures in the OD&D Supplement IV Gods, Demi-Gods & Heroes
Hyborian mythos (Conan): The Kraken (8 arms), Yama (8 arms)
Indian mythos: Devi (10 arms), Shiva (4 arms)
Norse mythos: Sterkodder (6 arms)
Dragon magazine #93 article "Nine Hells Revisited". The greater devil Kochbiel has 4 arms and wields 4 weapons.
From 1st Edition: derghodaemon (5 arms), squealer (3 arms), xaren (3 arms) and xorn (3 arms).
In the Forgotten Realms setting Garagos is the six-armed god of savage bloodlust.
2nd Edition The Nightmare Lands supplement. The greater dream-spawn called Ennui have four arms that each do 1-6 Hit Points of damage.
Adeptus Mechanicus Techpriests from have "mechadendrites" attached to them, but they normally are not very Badass. Although that depends entirely what part of the Adeptus you meet. There's your garden variety cog-head and then there's the Mechanicus Secutor who tends to be a walking tank with several gun mechadendrites modified to not carry holdout laspistols but flamethrowers...
Techno-magos Darioq was a perfect example. He weighed four tons, had four heavy weapons (two heavy bolters and 2 plasma cannons), multiple heavy melee weapons, and around 10 mechadendrites. In the course of the novel Dark Apostle, he rips off a Chaos Terminator's arms and cuts him in half. After being bathed in flames for several seconds.
The multi-limbed Badasses are Techmarines and higher Tyranid organisms. Also, to some extent, Warp Spider Exarchs with their armour-mounted, independently fired weapons.
And then there's Sulphus, the techmarine from Warrior Coven who has three mechanical arms and one organic one. These arms allow him to fly a speeder and use the turret at the same time as well as firing his bolter, something that would normally require three people. At one point, he uses two of his arms to hold on to a spinning Talos and the other two to rip an armour plate off. He then jumps inside, blows it up and does a walking out through the flames sequence like in the first Terminator.
Greater Daemons of Slaanesh (Keepers of Secrets, as they're known) have two regular arms (and often carry large swords or whips) and two arms with huge pincers. The Masque of Slaanesh is a Daemonette special character with three arms (one normal, one small pincer arm and one large pincer arm). Some of the parts in the current Chaos Spawn kit have things like arms splitting into several limbs or big spiky tentacles coming off the back. But then, this is Chaos, of course there is.
Every Tyranid has six limbs. Some have two pairs of legs, some have six limbs that aren't much use for more than moving. The rest have two (or six) pairs of arms. And both pairs are either blades designed to rip you apart or holding guns made to shoot small organisms at you (which proceed to rip you apart).mber of limbs. Their creators, the Haemonculi, like to do this to themselves too. To a lesser extent, Dark Eldar Scourges are particularly brave/stupid individuals who have paid a Haemonculus to make them capable of flight via surgical modifications to hollow wings and add wings and flight muscles.
Dark Eldar Wracks and Grotesques (hideous Frankstenian monsters, except they're made when the various parts are still alive and conscious)tend to have any number of limbs, some with incorporated weapons.
In Warhammer Fantasy Battles Slaanesh is fond of this (if Power Perversion Potential can be applied to it, rest assured there's a champion of Slaanesh who has it). His Greater daemons have this and his heralds can be given it.
Four Burning Fists and the Shiva Squadron from the "Glimpse of the Abyss" supplement have multiple arms, the former having four arms and the latter having eight arms like their Hindu god namesake. In addition, anyone who has the Creature schtick "Multiple Arms" can be Multi-Armed and Dangerous as well.
Plus there's "Three Pistol" Sammy Chung from a Feng Shui fansite, who's a demon with three arms (the third one in the center) that, as his nickname implies, specializes in a rather freaky form of three-gun Guns Akimbo.
The game Werewolf: The Apocalypse has the Ananasi werespiders, whose hybrid form has either six arms, six legs, or four of each (the player picks one at character creation). However, it takes a fairly high-level spell to be proficient at multitasking. It's also worth noting that the Bagheera wereleopards/panthers' most powerful spell is the Juddho form: a 12-foot, six-armed monstrosity in a state of frenzy for the spell's duration and wielding a flaming sword in each hand. Um yeah, one of multiple reasons why Vampires were never strong in India.
In the Promethean: The Created setting, Pandoran transmutations are capable of granting extra limbs. There is also a Sourcebook which provides a multi-armed fighting style. The title of the Prometheans who work to cause decay, the Centimani, means "Hundred-Handed". Most Centimani are usually content with a few extra pairs of limbs, tentacles and maybe some redundant organs, but there isn't much that stops a truly ancient, powerful and horrific Centimanus from adopting a hundred arms and fifty heads like Hecatonchires, their namesake monster.
Two examples from Vampire: The Masquerade. First and foremost are the Tzimisce, whose clan specialty, Vicissitude, allows them to mold living beings — higher levels and sufficient skill could allow them to grant extra limbs to whatever they desire. And their clan-exclusive Path of Enlightenment encourages experimentation. One such experiment was the bloodline called the Blood Brothers, who were created in packs and had an ability that, at higher levels, could allow them to "borrow" body parts (frequently limbs for attacking) from others in their pack.
Sol Invictus (the Unconquered Sun), the most powerful of the gods. He's invulnerable, cannot lose at anything, and sports a pair of extra arms.
Further, some Lunars and Fair Folk can obtain a second pair of arms as a mutation. Even some mortals might end up afflicted with it, if they're unlucky enough to stay in the Wyld for prolonged periods (ie, more than 5 seconds).
Alchemicals and Infernals can also get in on this action. Alchemicals can install Manifold Transhuman Implants to access mutations, while Infernals can manifest them with By Rage Recast or just bless themselves with Verdant Emptiness Endowment enhanced by Scoured Perfection of Form. Both allow multiple limbs among the mutations they can grant.
In the RuneQuest default world of Glorantha, the giant Grotarons (a.k.a. Trimanes and Maidstone Archers) have a third arm where their head would be (and eyes on the backs of their hands and a mouth in their solar plexus...) They use massive bows, held in their left and right arms and drawn with their top arms.
The Thieves of Fortress Badabaskor. The would-be deity Angall of the Perpetual Void had four arms. He normally fought with two +1 swords in his right hands and two +1 maces in his left hands, doing up to 72 Hit Points of damage per round with all four weapons combined.
The Treasure Vaults of Lindoran. In one room the PCs can fight a four-armed bear that's as strong as a giant.
Dark Tower. The Lesser Sons of Set and Chosen Sons of Set can have multiple arms. Manahath the Chosen, a Chosen Son of Set the PCs will encounter at the end of the module, has two pairs of arms.
One NPC villain in Enemies II (1982) was Grond, a 12 foot tall green humanoid with four arms and greater strength than most superheroes.
Adventurers' Club magazine #2, adventure "What Rough Beast''. The PC heroes must defeat a gigantic mutated bear with four arms and lethal claw attacks.
The Circle and M.E.T.E.. Two of the guest aliens at M.E.T.E. - T't'shlr (four arms and a lethal hand to hand attack) and Case 39 after it hatches (14 arms and superhuman strength). Case 39's mother has the same number of arms as its child and even greater strength.
The Hero System Bestiary had the Giant Squid (10 tentacles) and Giant Octopi (8 arms), both of which were quite dangerous to humans.
Orlens are humanoids with four arms. They all have the telepathy and telekinesis mutations, and some of them have additional mutations such as poison claws and devolution.
Any mutant can have the Additional Body Parts mutation, which can be 1-10 additional arms. One example is the menarl, a giant water snake with 1-10 arms and tremendous strength.
Call of Cthulhu has a number of deities and monsters that have multiple arms/tentacles and can kill a human being quickly. Azathoth (up to 6 tentacles), Being from Xiclotl (6 tentacles), Cthugha (up to 4 tentacles), Dark Young of Shub-Niggurath (4 tentacles), Flying Polyps (up to 12 tentacles), Gugs (2 arms, 4 forearms), Old Ones (5 tentacles), Servitor of the Outer Gods (up to 6 tentacles), Shub-Niggurath (dozens of tentacles), Giant Squid (8 tentacles).
The Chaosium supplement All the Worlds' Monsters had the following creatures: Air Squid (12 arms), Snake Ape (4 arms), Daughter of Kali (regular = 4 arms, Elder = 6 arms), Gnarled Gremlin (3 arms) and Telk (4 arms).
Earthdawn. The Horror named Hate had twelve arms and could make three attacks per combat round.
Rifts (and also Palladium Fantasy Roleplaying Game) have Rahu-Men, four armed giants who can wield giant-sized weapons in each hand.
Asura, an optional boss in Final Fantasy IV, had six arms and three heads. She's queen of the Feymarch / Land of Summons, and if you can defeat her (which is impossible if you don't know the trick) she'll allow Rydia to use her as a summoned monster.
And Gilgamesh returns for the prequel, morphing into his eight-armed form for his Super Mode (each of which wielding a random weapon from his repertoire, making his attacks more reliable than they were).
In Final Fantasy XIII-2, Jet Bahamut and his two fellow Bahamut helpers all have four arms, though they're mostly there so they can fight you while maintaining a Badass Armfold, using only two arms for their attacks the majority of the time.
Another Hindu-inspired demon is the Shivarra from World of Warcraft. Despite the name, they appear to be based off of the goddess Kali (or perhaps her much less evil but not much less scary aspect Durga).
Warcraft games have the above-mentioned Shivarra demons, aswell as female Nagas (male Nagas have only 2 arms). Undead abominations have a small extra arm sticking from their shoulder (they're created by patching together a bunch of corpses).
Subversion: Star Overlord Valvoga from Makai Kingdom certainly looks like it could be completely menacing, if not for the fact that multi-armed Micky is a complete pushover and is always bullied around by his other parts, the mad dragon-head Dryzen and the temptress Ophelia.
Her teammate, Screaming Mantis, also has powered armour that gives extra limbs: six, in Mantis's case, four of which are as unused as her actual arms, while the top mechanical ones are used for manipulating her Psycho Mantis and The Sorrow dolls.
Lord Recluse, who has four extra giant spider-like claw-arms affixed to his back. According to the book of the game, those are part of his body.
The mutated Arachnoids have the same claw-arms. The extra arms of the Crab Spider Soldiers are purely mechanical, though, although they are surgically attached and connected to the soldier's nervous system.
And the Meat Doctors of the Freakshow, who have limbs with rotary cutting blades grafted to them.
Mehrunes Dagon, Daedric Prince (read: god) of destruction of The Elder Scrolls, is always shown with four arms, each holding a different weapon. Judging from his mythologies, he's apparently another Shiva-inspired example.
Kazdan Paratus of The Force Unleashed built himself four mechanical limbs to crawl around Raxus Prime like a mad bug.
Planescape: Torment has Nordom, a Rogue Modron (see the Dungeons & Dragons example above) of the Quadrone caste, who uses his secondary set of arms to allow him to use two crossbows simultaneously. This makes him unique in the game, as all of the other Quadrones seen are "Messenger" variants, who have chosen to replace their second set of arms with wings that let them fly instead.
Subverted in Unreal: the locals of Na Pali (the Nali) have four arms and two legs, but are Non Action Guys. It's odd considering various critters (cow and rabbit equivalents)have only two limbs total, both legs. They also have floating 'gasbags' which consist of a wide head and two arms.
Asura, who can grow four Extra Arms. His final form plays this straight and averts this): he grows ONE THOUSAND ARMS, which then fuse together into two arms to create Mantra Asura.
Apart from Asura, there's also Vlitra's core and Chakravartin. When fighting the latter, he breaks all of Asura's extra arms and the armor over his last two arms, forcing him to fight — literally — barehanded.
Peacock: I've heard of armed and dangerous, but this is ridiculous!
In Phantasy Star Online 2, Dark Falz Elder initially has eight arms and grows two additional ones once he's been damaged sufficiently. He generally uses three of them at a time for direct attacks and launches lasers and meteors with the remaining ones. It's possible to destroy all but two of them, which both severely limits his attacking options and grants you extra rewards once he's defeated.
The Bleu Ringahda is another example of this, being a bird/centaur hybrid with an extra pair of arms. It wields a pair of lances with the lower pair, and initially just keeps the top pair crossed in a Badass Armfold, but when it gets serious, it'll start using them wield the pair of katanas sheathed on its sides.
Subverted when it's pointed out that a four-armed alien has the same type of eyes as a human, and as a result, even if he can handle four guns at a time, he can still only aim at one target, same as everyone else.
Grontar in the webcomic Zap!!: a huge four-armed mechanic.
In The Order of the Stick, this is one of Durkon's (as well as all the other dwarves thus far appearing in the strip) fears concerning trees: they have so many "arms" that they'd be able to attack you dozens of times per turn. That trees don't actually move doesn't dissuade his fears. They're just waiting for the right moment to overthrow us all.
Another show by the same creative team of Ben 10 that features a multi-armed character is Generator Rex, where the character Breach, a psychotic-emo girl dressed in a sailor suit uniform with her hair draping over her face who underwent mutation with the activation of nanites that resided within her body, has a another set of arms protruding below her original set of arms (while the forearms of her original set has grown monstrously huge!). Strangely, she doesn't really seem to use her additional limbs all that much even while in combat. They usually just like to hang around while her upper limbs get the job done. Occasionally, she has been seen using those extra arms of hers... to only mimic and move in concert with the gestures her upper arms perform. To be fair, her overly humongous upper arms kinda blocks the use of her lower pair of arms for anything but making gestures. And besides, she also has the ability to generate and create numerous portals on a whim.
The Third Arm Sash in Xiaolin Showdown acts as, well, a third arm for grabbing onto things. However, it is only used for its secondary ability to extend out to an arbitrarily long distance, so the characters can grab things out of reach. The only times it gets used in addition to both other arms is when the Monks use it to do chores.
Mecha-Shiva from The Venture Bros., at least according to the eponymous characters' court testimony against The Monarch.
Gadget Boy & Heather introduces a villainess with six arms and uses a spider theme. Unsurprisingly, she goes by the name of Spydra.
In the cancelled series Stripperella, a supervillainess going by the name of Pushy Galore has two (hidden) extra sets of arms due to, in her words, the fringe benefits of being a genetic physicist. After revealing her six-armed frame, she even tells Stripperella to call her Octo-Pushy. Sadly, she only gets screen time in one episode, though the slight perk is that she actually uses her six arms to do a multitude of actions that are lacking in many other animations featuring multi-armed characters (such as piloting and controlling a blimp with all six of her arms).
Several characters on Jimmy Two-Shoes. Molotov's unnamed wife has four arms, as do every Gnomans and the Racing Bugs.
In the Ćon Flux animated series, there was a very very brief shot of Trevor with a four-armed assassin. However, she was beset by bees almost immediately upon her introduction and was killed shortly (due to an allergic reaction to bee stings). Talk about one-shot.
In an episode of Danny Phantom, we are introduced to Pandora, a ghostly version of her Greek counterpart, but with an additional pair of arms.
In the episode "The Crawler" of the Extreme Ghostbusters, secretary Janine gets abducted by an insectoid king and was transformed into a moth-like creature with four arms. She later leads the king into thinking that she's truly transformed, and unleashes a ghost trap right in front of him by hiding it with her second pair of arms and wings that she acquired through said transformation. She gets better.
Regular Show features two four-armed characters, a wrestler going by the name of Four-Armageddon, and Death's Wife.
Mordecai and Rigby also become merged into a two-headed, four-armed form during "Video Game Wizards."
Ninjago: Masters of Spinjitsu. Big Bad Lord Garmadon and the Samukai both have (or had) four arms.
In Teenage Mutant Ninja Turtles (1987), the turtles get attacked by an alien four-armed female assassin in the episode "Divide and Conquer." Living up to this trope's name, she quickly mops the floor with them.
In the new turtles the mutant Spiderbites has several spider arms ontop of his head, which proves quite effective for fighting the turtles.
In the Megas XLR episode "DMV - Department of Megas Violations", Darklos the bounty hunter has an army of what seem to be humongous four-armed rhinoceri.
Zigzagged with the Elzar, the four-armed Neptunian cooking show host in Futurama. It was revealed in one episode that during the 3007 economic depression, he made something called "Human Broth" to feed impoverished citizens. (It doesn't take a genius to figure out what it was made of.) Of course, whether that makes him dangerous to humans personally isn't known, and he probably doesn't do that anymore. (Well, probably. Stranger things happen on this show.)
In the superhero-themed Buttons and Mindy episode "Super Buttons" from Animaniacs, Buttons battles a carnivorous spider person (the mayor's own words) atop City Hall, an anthro spider supervillainess with four arms. She puts all four hands to use operating a giant fly swatter to put Buttons out of commission.