Naruto takes this trope to new heights. Not only do minions and other extras actively exhibit the trope, but Naruto himself possesses the ability to make a good 1000+ clones of himself. To that point, if he creates 1-5, they're usually the key to his victory, but almost any time he goes over 10 or so (which turns out to be his most common strategy), they turn into cannon fodder, as their main weakness is that they usually go poof with just one hit.
The "Uzumaki Barrage" attack used against Gaara seems to avoid this trope since it relies more on the simple physical weight of the clones rather than their martial arts skill. It still fails more often than not, though. (Also because the theme song was playing at the time so it was to be expected that he was about to kick a lot of ass.)
There are two instances where the Law of Conservation of Ninjutsu fails to apply to Naruto. His "Shuriken from A Thousand Directions" technique utilizes mass numbers of clones to bombard a single target with shuriken. Also, in the beginning of the anime, his assault of Mizuki is conducted with hundreds of clones, which end up beating up the supposedly more skilled opponent into a pile of mush.
Post-Time Skip, after his Character Development frees him from being an Idiot Hero (to a certain extent), this blind multi-clone rush becomes a viable strategy, as Naruto realizes that he learns everything his clones learn. So, he charges an enemy with five or so clones, learns their strategies, and formulates his own plan.
This is played spectacularly when (in the fight between Kakashi, Naruto and Sakura) Kakashi takes down the aforementioned 1000+ Naruto clones using only tai-jutsu.
Ironically, the Shadow Clone jutsu itself seems to be a skill possessed by only a few, extremely badass ninja (everyone else uses non-physical clones or element based clones). Thus, the most effective way to personally apply the Law of Ninjitsu Conservation is itself conserved.
Shadow Clones are all over the board on this one. Officially, the user has to divide his power evenly between each clone, so all the clones are collectively as powerful as the user. Naruto bypasses this by having massive amounts of chakra, so he can make clones that are every bit as capable as he is. But most of the time they get taken out casually by a single opponent.
The show makes note of this trope: The standard squad is made up of four ninja. Kakashi says that any more and the team starts getting slow, clunky, and disorganized. A bigger team is worse at completing missions than a smaller one. Plus, any ninja that stands alone is pretty much Bad Ass enough to beat an entire squad.
Akatsuki has apparently gotten wise to this; in a nice show of Genre Savvy, they only workin two man teams. To give you an idea of how effective this is, each team is usually on equal standing with an ARMY.
During the fight of Sakura and Chiyo vs. Sasori, Sasori summons about a hundred puppets at once, most of were taken apart easily by Sakura and Chiyo's Ten Puppet of Collection Chikamatsu. Later in the fight, the ten puppets quickly lose advantage as Chiyo pointed out that Sasori controlled his puppets better as their numbers dwindled.
Averted during Madara's fight with the Bijuu, in which despite his strength and prowess, gets handily owned by the teamwork of the tailed beasts albeit he has no eyes. Then played horribly straight when he gets just one of his eyes back and becomes virtually unstoppable.
Ninja Scroll: Jubei eliminates ninja after ninja flunky with prototypical displays of gushing High-Pressure Blood. Only the Eight Devils of Kimon can give him a challenge; all others die with pathetic ease.
Played with in Ninin Ga Shinobuden, where Shinobu's fellow ninjas are faceless mooks who can't do anything right. Miyabi can defeat the whole clan easily, and she's about twelve.
Dragon Ball is a frequent offender, especially in plots involving the Red Ribbon Army or Frieza's men, but the most blatant usage is in the Bardock TV Special. As he races to attack Frieza in the climax, he has to fly through an army of mooks, which cause him so little trouble that, in some cases, they look like they're splattering on his face.
Anyone in Dragon Ball who possessed the ability to duplicate themselves usually followed a similar rule, because the person using the technique actually does divide his power up evenly amongst his clones. So a fighter with a power level of 2400 becomes two fighters with power levels of 1200 or three fighters with power levels of 800 and so on. The creator of the Division technique actually gets criticized by his rival for creating a move with such a debilitating flaw.
But subverted by Metal Cooler in one of the movies. After one copy is defeated, hundreds more show up... each of whom are just as strong as the original.
The movies in general are better about this. Sansho, Ginger, and Nicky manage to take down Piccolo with a Combined Energy Attack, despite being individually weaker than him, Bido, Zangya, and Bujin are able to take down the powerful Super Saiyan Gohan with teamwork, and in the above Metal Cooler example, Goku and Vegeta managed to defeat the original Metal Cooler by combining their energies. Generic mooks also manage to take down Gohan and Krillin in the Lord Slug and Metal Cooler movies, again by ganging up on them, despite sustaining heavy losses.
In the History of Trunks, it is implied that Gohan is about as strong as one of the androids. Too bad 17 and 18 attack as a team, completely overwhelming Gohan.
Hellsing does use this. The Hellsing Organisation's operatives mop the floor with masses of enemy ghouls but find more trouble in dealing with lone strong vampires. However, there is also a lot of subversion. Seras assisted Alucard against the lone Tubalcain Alhambra and helped her side win instead of making the odds worse, as the Inverse Ninja Law would have. Similarly, when Alexander makes his one-man charge towards Alucard and a newly-summoned army of familiars in a later part of the story, he finds that the numbers actually are to Alucard's advantage and it takes reinforcements to save him.
Made more explicit in OVA 8, where a count of how many members of each warring faction remain by the time Alucard, Anderson and the Captain meet is done before the climax. Guess which side gets wiped out first and who comes out victorious:
Army of the Roman Catholic Church's 9th Crusade: 2875 men.
Members of the Last Nazi Battalion "Millennium": 527 vampires.
English Protestant Knights "Hellsing": 2 vampires and 1 human..
Like so many other times in this franchise, however, this is almost immediately subverted after the count is made as Alucard quickly summoned millions of familiars to completely overwhelm the other two forces with a very literal tidal wave of fresh troops.
Played with a lot in Digimon. Digimon Adventure, 02, and Tamers subvert it (divide and conquer is a common and effective strategy on heroes and villains alike, anyone can be overwhelmed by enough numbers, etc). Digimon X-Evolution both plays it straight (the original is vastly superior to the copy) and subverts this, by the Digimon defending their lives being worn down gradually to their destruction. Surprising, for a shonen (or is it kids? ) anime.
Digimon The Movie plays this very straight for both the heroes and Diaboromon, whoever has greater numbers tends to be on the losing side. Wargreymon and Metalgarurumon can barely get a hit in on Diaboromon in between all the asskicking that he's giving them, but when he multiplies into several thousand copies and they becomeOmnimon, the army is mowed down within seconds. When he gets to the last Diaboramon, the fight is now one-on-one and is more evenly matched (if only because he's too fast to hit).
Two resident Obvious Ninjas, one plays this straight the other subverts it slightly. Inugami Kotaro can't create Shadow Clones of equal power to himself (and his cap was seven in the Tournament sub-arc). However Kaede with her Sixteen Shadow Clones CAN... but not at full count. When she has four shadow clones they are all equal to her alone. Proving with Training at least in Negima you can bypass this trope.
Later in the series the main lead's father Nagi and his team the Ala Rubra were fighting in The Very Definitely Final Dungeon against the absolute Big Bad. A single sneak attack from him was enough to wipe out the entire party. Then, after being healed, Nagi managed to single-handedly take out the Black Cloak wearing Ultimate Evil. Hammering the point home, each individual member of the Ala Rubra were more than capable on their own against their stylizedPsychoRanger opponents they'd faced previous.
A textbook example occurs in chapter 254. Negi takes down a small army of Governor Godel's elite "private bodyguards" in a matter of seconds, but when he fights Godel one-on-one, the Governor takes his legs out before he can react, then nails him with a barrier piercing attack whilst he was unable to dodge. Negi was on the floor before he knew what hit him.
An even more textbook example occurs in 314 and beyond. While Fate Averruncus is a massive threat capable of taking out Negi and characters beyond his level like Rakan, the three Averruncuses mentioned to be every bit his equal get laughably curb-stomped and one-shotted in back-to-back chapters the moment they try to go against the people at Negi's power level, complete with notes from Fate about how soft their attacks were.
In Berserk, Apostles were a major threat early in the series, with Guts needing to fight with everything he had to kill one, and Guts probably would have died fighting the Count if the Count's daughter hadn't conveniently burst into the room for Guts to use as a hostage. Now that all the Apostles in the world are serving Griffith, they've been demoted to Elite Mooks. Justified, since Guts has the Berserker's Armor, which makes him much stronger and brings out his Superpowered Evil Side.
Wylad and Zodd both nearly kill Guts, Zodd stops when he sees Griffith's Behelit and Wyald (after being stabbed through the face and neck) is only put down when Zodd shows up and tears him in two for his insubordination to the God Hand. When the eclipse happens Guts tears through dozens of Apostles, tearing off ones horn and using it as a spear. Sadly this trope doesn't extend to the other Hawks...
Yu-Gi-Oh! GX sometimes shows a character (usually Manjoume/Chazz) defeat several duelists at once offscreen. In Manjoume's case, apparently it's his coattails of doom that makes him elite enough to do this.
And in the original series, Prescia Testarosssa took out a platoon of magical enforcers in a single attack, while Nanoha and crew ripped through her automatons with ease.
This trope is subverted with Ginga, who was defeated by three Combat Cyborgs despite being a better fighter than all of the Riot Force 6 recruits. Also by Teana, the weakest among the Riot Force 6 recruits in terms of magical power, but defeated the most number of Combat Cyborgs by outsmarting them.
One Piece: The Straw Hats are attacked by a horde of Captain-ranked Marines. Each one displays unique powers, fighting skills, or weapons. Each one a few chapters ago would have been a boss, or at least a major enemy. Now, they were dangerous only because of their sheer numbers.
Morgan was also a captain, and Luffy defeated him without taking a single hit. T-Bone was an Elite Mook, and while he presented a threat to the Rocketman, Zoro defeated him in one hit, so the strength of Captain-ranked Marines is not that significant at this point in the story.
Quasi-invoked by Tashigi during the Alabasta arc. While staring down Nico Robin with a veritable army of Marines, she realizes who Nico Robin is, notes that "numbers don't mean anything to Robin," and sends her army away to fight Robin one-on-one. She immediately loses. Perhaps you have to be a main character for this to work.
One Piece does this to the point of ridiculousness. During the Assault on Enies Lobby, Luffy single-handedly defeats an army of 2000 Marines without receiving even a scratch. Immediately afterwards, he fights one-on-one against Blueno, who gives him significantly more trouble. However, given that Blueno was an elite agent and the Marines were just foot soldiers, it's somewhat justified.
The Enies Lobby assault in general was a massive invocation of this trope. The Frankie Family and Straw Hats numbered about 60 and in total there were about 10,000 soldiers on the island. That's right—taking down one of the World Government's strongholds housing the CP9 and a garrison of 10,000 strong took only 60 people.
The start of the Whitebeard War seemed to be pretty even too, even though Whitebeard's men totaled only those on his four ships plus about 40 other crews from the New World. The Navy, on the other hand, had 100,000 soldiers. To be fair, most of those were still further down in the plaza, but it's still a pretty massive example.
An army of fishmen numbering 100,000 fights against the Straw Hats and Jimbe. The opening move in their battle consists of Luffy knocking 50,000 of the enemies unconscious simultaneously.
By STARING at them. Although it is kind of justified as this is an ability that you have to be born with and only a really small portion of the people in the world have it and is one of the most powerful abilities in the world. Also they were all Redshirts by this point in the story.
Afro Samurai is made of this trope. Afro will triumph over any number of foes attacking in numbers, but have trouble one-on-one.
Yakitate!! Japan! inverts this by having Kageto Kinoshita's only endearing trait be his ability to clone himself. He is full of so much suck that his power alone is zero anyway, so making clones can't hurt.
One of the manga of Ah! My Goddess, shows Urd demonstrating her copying ability, in an omake, and explaining, as she gets into the hundreds or so of copies, they start to become, well... jelly...
In the first episode, they face a single one of Talpa's samurai Mooks. It takes the entire episode and the Hero summoning his armor and using his Finishing Move to take him out. Any subsequent attacks by them can generally be handled without transforming, and in the second arc, two of the heroes can take on hundreds of them.
The first episode itself could be a subversion. That mook was using Anubis's weapon.
Watch an episode of Sailor Moon and you'll have the basic formula: Sailor Senshi weaken monster, Sailor Moon finishes it off. Now watch one of the movies, where there can be dozens to hundreds of monsters at once, and EVERYONE will be able to pick them off with an attack or two.
Somehow averted considering said Sailor Senshi don't have much trouble defeating the lone monster even though they outnumber it.
All throughout Claymore, Awakened Beings are shown to be extremely formidable, requiring several Claymores banding together to outnumber them in order to defeat them, and even then only barely and requiring multiple episodes dedicated to the fight. In the final arc of the anime when the Awakened Beings attack en masse, they don't take near as much effort to kill as previously. Though this is only as a result of the anime's Gecko Ending. In the manga, despite gathering half of the Organization's warriors, they only manage to kill eight Awakened Beings before being wiped out. The Awakened Ones' field commander actually notes that this was an exemplary result for the Warriors.
In Noir, any time the two assassin protagonists are badly outnumbered, every bullet of theirs seems to kill two enemies, while every enemy bullet misses its mark. When they face Chloe however, they meet their match.
Any nameless mook in Utawarerumono is canon fodder and will die in the dozens per sword slash from a general or important character. The large scale battles are really battles between named characters. The mooks on either side are just window dressing and will not get any kills in.
Hibari taking on an entire army of Millefiore soldiers and coming out fine only to get beaten when he goes one on one against Genkishi.
Most recently with Hibari again during his match with Adelheid. In their one-on-one before they were about even, but now it seems that 500 Ice Clones of Adelheid, who have her same strength by her measure, can't even scratch Hibari.
And Hibari goes for a hat-trick, taking out three of the Varia in a single hit. It seems like his entire strategy in this arc revolves around this, as his entire team consists of nobody but himself.
Gundam SEED Destiny plays this to high levels, with highly possible (but unconfirmed) Justification. A single Destroy Gundam helps the Earth Alliance to stomp over much of Europe, takes multiple episodes to go down and the repercussions of its destruction linger for several episodes afterward. When the EA field three, they go down in the same episode without too much trouble. When they field five at the same time, it's almost a non-event. The Justification is: 1. Stellar, a Tyke Bomb piloting it, while these mass-produced unit are issued to Mooks, also 2. the one she rides is shown having MORE feature than the mass-deployed (although STILL unconfirmed), in short, Super Prototype.
In the first series of Full Metal Panic!, most major arcs end with a showdown between the protagonist Sousuke who fights the Big Bad Gauron, who fights using an Arm Slave equipped with a Lambda Driver, which makes it nigh invincible for all intents and purposes. In each encounter, Sousuke is pushed to the brink of his physical limits just trying to take down one of these things. At the end of Full Metal Panic: The Second Raid, he has an encounter with five enemies who are using the same invincibility device he struggled against in season one, and dispatches all five of them with relative ease.
Somewhat justified in that in the fights with Gauron, Sousuke either had trouble with or failed to use his own Lamda Driver. In the fight at the end of TSR, his Driver is functioning perfectly, allowing him to fight on an even level as his enemies and beat them with his skill and their reliance on their Lamda Drivers saving them.
Saito from Zero no Tsukaima took on about a couple thousand soldiers alone at the end of the second season and took down most of them before falling and being revived by a wood elf?
Significantly subverted in that the light novel tells us that he managed to take down only about 250 of them before falling, which isn't a large amount - numerically - given that he was fighting against 70,000 of them. Admittedly, he did manage to stop them from pursuing Tristain's fleeing army, though, so it still certainly serves as an example of the trope.
The 250 were high ranking officers he deliberately targeted to cause confusion, he didn't kill any of them. Also worth noting his sole purpose was to slow the army down until his allies could escape, which he succeeded.
Averted in Holyland. Yuu can win one-on-one duels, but usually does poorly in a target-rich environment.
Generally, the main characters only ever struggle against very powerful single opponents. Being outnumbered has never caused them problems (especially for Inner Moka). She and Tsukune alone manage to wreak havoc on the athletics festival.
Highly present in Rurouni Kenshin - somewhat justified in that Kenshin's Hiten Mitsurugi style is specifically mentioned as an exceptionally rare and deadly style (no more than two people are masters of it at any given time, and Kenshin chooses to let it die with him) that specializes in combat against multiple opponents.
Inukami!: Sendan's group, even as a whole, is less powerful than Youko is by herself. Subverting the trope, they're even worse off when fighting individually.
The Mazinkaiser OVA bounces around with this. The Mazinger Team goes off to fight Dr. Hell's Mechanical Monsters and lose badly, only for the monsters to get trounced when the titular Super Robot finally appears. It's played much more straighter at the end when Great Mazinger takes on all of Hell's monsters and wins.
Getter Robo Armageddon. On one end, an entire army of Getter Robo G, the second of the Getter Robo line. On the other, a singular classic Getter Robo, piloted by Ryouma Nagare. Ryouma owns them easily.
Conversely, in Shin Getter Robo vs. Neo Getter Robo, Shou and Gai are overwhelmed in the Neo Getter Robo when dozens of prototype Getters piloted by members of the Dinosaur Empire attack them. In this case, though, it's not a matter of Conservation of Ninjutsu, but the fact that, despite being prototypes, the dozens of Getters were using Getter Energy, thus are much stronger than the plasma energy-using Neo Getter and it doesn't help that Getter had only 2/3 pilots.
Two legendary Gundam scenes are made up of this trope. In the original Mobile Suit Gundam, Amuro's awakening Newtype powers are revealed when he pushes the RX-78 Gundam to take out 12 Rick Doms, then Zeon's newest and strongest Mook unit, in three minutes. 20-some years later, Kira uses the Strike Freedom Gundam to defeat 12 GOUFs in 2 minutes in Gundam SEED Destiny.
This is a pretty common trope in Gundam media, 1 ace pilot will take out dozens of mooks on either side of the war regardless of whether they're fighting for or against the good guys without taking a scratch, only when it's ace vs ace do they end up losing. Possibly justified as the aces are not only the best pilots on their side, they usually in some of the best mobile suits their side has to offer.
Subverted in at least once instance when Heero ended up fighting in one of the the mass produced Leo mooks he was quickly curbstombed along with his similarly equipped allies by the much better Taurus mobile dolls.
This trope is played with in Mobile Suit Gundam 00. At the start of the first series, the Super Prototype Gundams steamroller all non-GN-powered suits... Until one episode, where the world's 3 main superpowers team-up to defeat them, and it almost works, if not for The Cavalry showing up. Then, when Mook tech levels catch up, the Gundams are on the back foot again... Until the second series, where it zig-zags it. The movie, on the other hand, averts this trope nicely. The ELS, which number in the TRILLIONS, trounce the mere hundreds of thousands of Earth forces, Gundams included, with barely any effort, and would easily win, if not for Setsuna.
Akane of Ranma ½ vs half the guys in the school. Multiple times in multiple episodes, and presumably tens of times offscreen. Sounds like a fair fight...Justified in that she practices martial arts extensively, whereas most of her opponents train fighting as a hobby if at all. However, some few of her opponents are judoists and a very noticeable sumo wrestler...
An episode of HeartCatch Pretty Cure! had Cobraja create an army of Desertians through children's unwillingness to do their homework over summer break. For the most part, these tiny Monster of the Week are just annoyances. It's when they become a full-fledged monster that the girls are given trouble.
Also happens in Pretty Cure All Stars DX 3. Two of the teams of Cures (the leader group of Cures Black, Bloom, Dream, Peach, Blossom and Melody and the bright colored group of Shiny Luminous, Milky Rose, and Cures Rouge, Lemonade, Pine, Passion, Sunshine and Moonlight) deal with groups of Monsters of the Week with ease, but the remaining team (soft colored group comprised of Cures White, Egret, Aqua, Mint, Berry, Marine and Rhythm) are put through the ringer with only a small group of monsters.
Yoko's gun is hard pressed to take down a single gunman, but in the battle with Die-Gunzan, she takes down many with ease.
Later, in that same battle, their team gets nearly destroyed by a comparably equal force, but when attacking the Spiral King's stronghold, the same team plus a few additions take down clouds of Gunmen almost comically, surviving with ease.
It is sort of averted after the time skip when almost everyone dies, but even then, they seem to be powerful against many of the same type of enemy, of which only one gave them trouble mere minutes before.
Fairy Tail, to the point that you can predict the outcome of any given battle. Every time the heroes team up against their enemies, they're going to lose, but when they fight those same enemies by themselves later, even 1v2 or more, they win.
Actually averted against King Faust, but to be fair he was in a giant mecha at the time.
Also averted against Master Hades of Grimoire Heart. However, Natsu got the main credits.
Played straight with every dragon they fight. A dragon is strong enough to defeat several guilds.
In Puella Magi Madoka Magica, individual witches are unique, have names, and are highly dangerous. Some are capable of defeating multiple Magical Girls singlehandedly. In the last scene, Homura is shown fighting "distortions" (the replacement for the erased witches), which are more numerous than witches and apparently much weaker, since she takes on several simultaneously and nonchalantly.
Fate/Zero's Assassin invokes this trope; his body-splitting ability divides his stats among the split bodies, making each one very weak. But the trope is ultimately subverted when all the Assassins are trounced by Rider's army, which greatly outnumbers them. And then it's played straight when Archer effortlessly defeats Rider and his entire army, thanks to his ludicrously overpowered universe-destroying Noble Phantasm.
Noticeable in the first part of JoJo's Bizarre Adventure. Dio kills a sizable amount of Supernatural Martial Artists despite (presumably) not possessing any abilities not inimical to vampires; however, the same team of martial artists has no difficulty in taking down large mobs of the same vampires.
Averted/subverted in the next part, as Joseph and Lisa Lisa recognize the threat of being surrounded by (literally) a thousand vampires, and choose to retreat instead of facing them head-on.