In Dynasty Warriors: Gundam, Wing Zero's beam attacks can pierce enemies without the Piercing Shot skill. Its SP attacks, once fully developed, are as follows: first level is firing the Twin Buster Rifle at full power directly ahead, level 2 has Zero hovering in mid air and firing the rifle down, and finally it splits the rifle in half and spins like a top, firing beam in either direction. If you use the SP attack in tandem with another named character, Zero will do another spin attack, angling side to side to hit enemies above or below. Coupled with the simple enemy AI, and the SP attacks being the easiest to aim, and it's likely that whatever survived that onslaught is just about dead.
In Dynasty Warriors Gundam 2, Wing Zero isn't quite the death machine as before, with tougher enemies and altered SP Attacks; Wing Zero's spin attack is its combination SP Attack. Nu Gundam though, has a charge attack that launches its Fin Funnels and have them form a barrier. When this field is being brought down, it can kill just about any Mobile Suit in one hit. Once you've cleared a field, the barrier can bring enemy mechs to near death by running into them. The best gamebreakers are some of the pilot skills. DG Cells lowers defense, but grants a fast-acting Healing Factor, and Overdrive enables the combination SP attack for one character. This makes Wing Zero, Zeta Gundam, and ∀ Gundam monsters in battle. Especially Turn A Gundam.
In the second game, the God Gundam's Overdrive skill causes it to split into three versions of itself if you use it when the SP gauge is completely full. Combine this with its God Slash Typhoon, which is the strongest Melee attack in the game, and you can render your opponent dead or very close to it in two moves. Some players call it "the blender."
One strategy for both the second and third games is play with just one character over and over. Since you'll play the same stages with the same enemies, you can level up the other Gundams and MS before using them with the other characters. This makes their stages much easier.
Unicorn Gundam in the third game is especially this. Like Master and God, Unicorn enters its own Super Mode when it uses its SP attack. Both of them can effectively deplete an enemy field's gauge in less than a minute with Lv 4 Plan with a large amount of upgrade slots. Its Beam Magnum, although having a slow fire rate, is absurdly powerful and its last Charge Attack could count for an SP Attack altogether and it can be aimed. With a lot of enemies around, you'll be spending an extended time in NT-D Mode from the ridiculously long and extended range combo chains.
00 Raiser is also this with the right plans and Upgrade Slots. Its maximum level SP attack practically lifts every single on-screen enemy in front of it into the air and will most assuredly kill them on the spot. Its special equipment also gives it extended time in Trans-AM which already gives an extended range similar to Unicorn with added effects to its Charge attacks
Some would consider Dynasty Warriors's Lu Bu a Game Breaker, since in all incarnations of the series he is playable. Mostly for his C3(Square-Square-Triangle) that covers 360 degree and have multiple hits coupled with powerful damage. In fact, the fourth game version of Lu Bu are not gamebreaking maily because said move are hit by a Nerf.
KOEI's Warriors Orochi 2 lets you use Orochi — the Big Bad of the first game, and you needed to unlock everyone else in the game before you got him — as a starting character. He's still as powerful as his playable equivalent in the first game. There may be other questionable starting character choices (such as MiyamotofreakinMusashi), and as a NPC Sun Wukong's moveset priority is annoying, but he stands out rather well as a playable character.
Sun Wukong + the 'Almighty' weapon ability makes any stage a breeze. Even on Chaos difficulty. (For that matter the 'Almighty' weapon ability is a win button for anyone on the roster, but Sun Wukong's movement speed make it even more of a win button).
There's also Cao Ren's C3-ex (Square-Square-R1) in the sequel which basically clears the screen againt anything, and he can spam thanks to his absurd Musou regeneration from said move. To make it worse, hes one of two Technique character with two enchanced special moves, and his second listed move(the C2-ex (Square-R1) have insane coverage, refills Musou gauge even more than the cost of the move, does massive damage. Oh, and his C-3 doesnt even need Flash to break guard because the AI never blocked that move. Even in the Z version of the game, hes still broken. Theres a reason why the second game's Cao Ren is widely considered to be one of the most broken character ever in Warriors game.
Diao Chan's Triangle/Y attack from the first Warriors Orochi combined with the right weapon destroyed hordes in no time.
Kunoichi R1 which gives you complete invulnerability to anything for the duration. In the first game, it only lasted 10 seconds, but with proper set up(the right weapon, and only use her C2-1) you can kill an officer in a flash, refill her Musou gauge and use it again essentially creating an invincibility loop that is near impossible to break. In the second game, instead of nerfing it, for some reason Koei decided to extend the duration and make an enchancement that gives you faster musou regeneration while keeping her musou recovery intact. To put it simply, she is a Japanese character who plays so much like most high tier Chinese character(which mostly a Game Breaker in their own rights) in the first game and taken Up to Eleven.
Taigong Wang's musou. It has a rather weird range but it does MASSIVE damage, so much that it can One Shot anything. It can be blocked but his C1 break his opponent's guard and put them on Recoil stage. Obviously the Updated Re-releaseNerf it.
Huang Zhong in second game. His arrow spread C1 normally carries no element. But with R1, it does. It also self sustains the Musou Consumption with full absorb and dealt damage so massive that it can one shot anything in one shot, making him a Cao Ren-lite. Heavily nerfed in Z though.
In the first game, because of how the element system works with the Samurai Warriors roster, KOEI decided that that almost every multi hitting charge attack outside of C3 for the Dynasty Warriors roster carries elements on each hit and decided that the C1 and C2 that didn't have elements from the get-go would activate elements as well. This turned out to be a very bad idea. C1 attack that involve charging to enemies ranks become an I-Win-Button, C2 become a really fast, reliable way to juggle and activate element, therefore dealing quick massive damage, and multi hitting charge become insane damage dealer. This is the whole reason why some of Dynasty Character is very effective and why some characters notably Guan Ping(whose C4 does 3 ELEMENTAL hits), Cao Ren(whose arguably the best C1 Stomp user thanks to his versatility on setting up the Stomp loop), Diao Chan(very spammable C1 and dual elemental C4), and Zhang Liao(Essentialy, Diao Chan without her C3 and weaker C1 that have even better crowd clearing as a compensation) is very broken(to the point that Diao Chan is considered as the best character in the game) This is nerfed in second game by having C1, and C2 no longer carry element and nerf some charge attacks.
In a game where Musou bar is very important due to the existence of some broken Musou related moves, characters that can abuse musou are pretty notable. Sun Jian's Directional R1's effect allows the team to have 10 second full musou refill in exchange for some Life. Combine this with character with abusable R1 move(ex. Mitsunari Ishida), and Technique Characters that have Special and enchanced Charge attack that consume Musou to abuse this Up to Eleven. The downside of this is the fact that it consumes Life, which is easily handled by giving Sun Jian Weapon with level 10 Drain(and the fact that Sun Jian is affected by elemental C1 issue mentioned above)
The second game tried to Nerf him by nerfing other characters' Musou related moves, and the general nerfing on DW character seems to be enough to put an end to his Musou spam days. However, other than the fact that some Musou dependent attack still murders with Sun Jian's enchancements, the Triple Musou system is introduced. Normally, a Triple musou need you to be at red health to be used, but with Teamwork enchancements, it can be used anytime. With Sun Jian's D-R1, there's enough time to do 2 Triple Musou, enough to kill the majority of enemy in the game. Combine this with the fact that his D-R1 now cost less Life, and he has Special Triple Musou with Cao Cao and Liu Bei which can be activated up to 4 time for each D-R1, 3 with some set up before usage, and you get a character that can safely kills anything
The third game removed most of the above strategies due to Technique characters losing most of their additional R1 attacks or changing them to something weaker (the most blantant example being Kunoichi losing her invincibility move in exchange for an useless kunai toss attack), but also introduced many other equally broken characters and tricks: for example, Xu Huang can spam his Ex attack all day which makes him take Scratch Damage from everything even on Chaos difficulty while everyone else goes down in 5-6 hits, Xiahou Ba's special attack turns him into Lightning Bruiser without equal and can easily gain back the musou it costs to use while it's active and using a team of 3 characters with the officer skill Thrift with one of them being a Samurai Warriors character easily allows them to stay invincible for minutes at a time and can replenish that time limit with little effort.
KOEI again, but this time in Dynasty Warriors 6: Empires. Sun Quan's card, 'Unseen Rules', means the player will never get invaded. Ever. Played with the rest of the Sun Clan's cards, the player can dominate China in relatively few turns with ease.
Dynasty Warriors 7 allows in-battle weapon switching, for any character to just about any other moveset (with varying degrees of efficiency and effectiveness). One particular moveset, Twin Axes, has a four-hit charge attack that puts a single target into stunlock at the end of it. Now consider the "Attack Up" and "Officer Assassin" skill seals, which increase power in general and against officers in particular, respectively. The Twin Axes then become so comically overpowered that they can kill even a supercharged Lu Bu in a matter of minutes, to say nothing of other player characters or lesser generic officers.
Lu Bu himself is a gamebreaker, as he's the only character in the game who can stack Synergyx3, giving him truly immense attack power. And since his Halberd moveset is still very dominating due to having both pinpoint unblockable attacks (his C3-EX and his C5 both cannot be blocked, and the C3 is a crowd clearer on completion to boot and makes him invincible once he's grabbed an opponent), he tends to stand out even though anyone can use his weapon.
Thanks to the medal system in DW 7, Extreme Legends; the best combination to have is a high-level wind weapon and a high level slash-elemental weapon. Many characters gain health back with every hit from a speed weapon (the sword), making it impossible to go into a crowd and come out almost no worse for wear (each combo is likely to gain everybody's health back for each use).
In Dynasty Warriors 8, Zhong Hui and Wang Yuanji's 5th weapons are simply made of this. Zhong Hui's 5th weapon has lv.10 Cyclone skill, which causes huge damage even when enemies are guarding and Yuanji's 5th weapon has lv.10 Jubilation, which restores your life for each enemy ko'ed. Having those two is a good replacement for those without time and patience to create a strong weapon in ambition mode.
The ambition mode's temper. Sure, it's a boring and time-consuming proccess of grinding weapon materials, getting gold and choosing the weapons you want to beef up. But with some patience, you can have Jubilation, Induction (AKA thunderbolts in every attack), Cyclone and velocity, thus creating weapons that can even surpass the DL Cs in terms of power.
Daqiao, Zhong Hui and Zhou Tai have broken weapons also in terms of something else: If you keep cancelling certain attacks with jump (Namely Daqiao's pugil sticks Jumping C1) you can travel across any battlefield easily.
Partially justified for being the Big Bad, but Fist of the North Star: Ken's Rage 2 has Kaioh. All of his moves have huge range and power, and pretty fast recovery. On top of that, by having him use a 5 Aura Scroll Nexus he can use his final Signature Move for a measly two Aura stocks. Said signature move covers a huge area and it lasts for a while. Go to the middle of a crowd, press circle, and bam, instant 50 enemies killed and guaranteed A Rank base overtake.
Toki on a minor scale for his C4. He sends two waves that kill any mooks in their way and deal decent damage to bosses. In fact, while it is not the best strategy for speed runs, Toki can pretty much stay in the other side of the stage sending his waves agains the boss (wich will actually fill the player's Aura gauge) and occasionally steeping in to deliver a Signature Move.
Saint Seiya: Sanctuary Battle has Phoenix Ikki, who is available right off the bat. While he's already very powerful for a Bronze Saint, he really shines once the player spend some Cosmo Points to upgrade his Phoenix Wing to Lv. 10. Once that's done, he's able to kill waves of enemies and even bosses without ever needing to get close to them, much less using a single punch - Phoenix Wing is the best projectile in the entire game, it comes out instantly, doesn't fade by hitting walls or ground (and its range is IMMENSE), juggles the enemies dealing multiple hits (more than enough to kill mooks and deal huge damage to bosses), and at Lv. 10, it is extremely powerful and cost a measly 400 Cosmo a pop (wich it often recovers by itself due to hitting many enemies each one a lot of times). Watch as he kills 20 mooks by pressing circle once and laugh as Gold Saints fall before even finishing their introductory quotes.
Wolf in the multiplayer mode of Star Fox Assault has insanely high health and speed stats, and the only balance on him is that he has a smaller targeting reticule when riding an Arwing or Landmaster. He is the only character who can survive a Demon Sniper shot, and he's very fast.
Also, Slippy, of all people, is incredibly broken in every situation outside the Arwing. On the ground, because of his high jumping ability, you can basically just keep jumping around in front of your opponent and completely dodge whatever they're doing while taking potshots at them. Combined with his above average health and his dominance in the Land Master, he's easily broken on maps where ground combat is an option. His only downfall is in the Arwing, where he's rather weak compared to most other characters. And he doesn't need to be unlocked, unlike Wolf. Peppy is arguably even more broken than Slippy using the same tactics.
In the unreleased Star Fox 2, there were three different ships in the game—Fox and Falco were the fastest, Peppy and Slippy were the toughest, and Miyu and Fay were the strongest. The problem lies in the definition of "strongest." Miyu and Fay start out with level 2 weapons and have half the charge time of the other ships. This makes boss battles much quicker. They only downside is that their ships are made of cardboard, but the shortened battle time more than makes up for it.
Star Fox Command has the Black Rose, a ship exclusive to Panther Caruso. At first glance, it seems to be a horrible ship - it's made of cardboard, has no lock-on, and its bomb capacity maxes out at 1. However, its basic laser attack is overpowered to an absurd degree. It can one-shot many of the endgame-level enemies, and those it can't are nearly always two-shotted. It can kill boss-level enemies in ten shots, and the final boss in around twenty. It also has a hitbox that is so much larger than its sprite, you would think it was a Wave Motion Gun; this means that aiming in something's general vicinity pretty much means you will hit it. Oh, and to make up for the aforementioned made-of-cardboardness of the Black Rose, it is tied with the Arwing II and Wolfen for the second best barrel roll in the game - in a game where the barrel roll nullifies ALL damage.
Star Fox Adventures gives us the Bafomdads, which revive you back to full health whenever you die. They are plentiful, but you can only carry one at a time...at least until you buy the Bafomdad Holder, which allows you to carry ten. You will never need to worry about dying ever again once you have this, and it is actually cheap enough to buy as soon as you get your first Scarab Bag (and you'll find more than enough scarabs within the store itself!)
Several players of Cave Story claim that the Level 2 Blade is one of these. At first glance, this seems confusing; it has less range than both its previous form and its following form, the game's lack of diagonal aiming makes the slight widening of range from Level 1 to Level 2 a negligible benefit, and the Blade as a whole is a single-shot weapon. It's the definition of the third aspect, though, that adds credibility to the claims — "single-shot" translates here as "the last shot can't be onscreen before you can fire the next shot." The Level 2 Blade at point-blank range does the most damage per second of any weapon in the game. Therefore, by getting dangerously close to bosses and mashing the fire button, it's possible to spam the Blade repeatedly and kill almost any enemy in the game in a matter of seconds.
On the other hand, the Spur doesn't require leveling, only charging, and does the most damage outside the level 2 Blade at point blank, and does it at any range. And you get it midway through the game, if you're willing to put up with keeping the dinky Polar Star despite several offers of trading it for better weapons.
The secondary effects of the Ring of Lightning in Little Big Adventure II can easily turn it into a Game Breaker. The item in question is, essentially, a spell that requires a full bar of Magic Points to be used. Its only plot-forced usage involves getting another item that can't be accessed without the spell. When cast in a random place, the Ring of Lightning still empties the Magic Points bar... effectively working as a "kill all enemies on screen" item, regardless of how many normal attacks you need to kill them. This extends to the tough huge enemies that normally require a lot of time and efforts to defeat them. If you get killed and lose an extra life (represented by a clover leaf), your magic is restored to full, allowing you to use the spell again. You can have up to ten clover leaves by the time of the final showdown (with extra leaves scattered all around the Big Bad's place), which provides a "cast spell - run - get killed - cast spell..." tactic instead of "run - avoid enemies - blow up teleporters to stop enemies from appearing - run...". The first tactic saves a lot of time, but this is just the beginning. The Big Bad is immune to your weapons except the Emperor's Sword, suggesting that you should have a sword fight with him, just like in the first game. He isn't immune to the Ring of Lightning. It kills him instantly. Way too easy for the final battle...
The Otana and the Missile Boat in the X-Wing/TIE Fighter series of games were easily the most powerful player-controlled craft in the game. Both of them allowed even intermediate players to slaughter capital ships singlehandedly, to say nothing of mauling squads of enemy fighters.
For those who haven't played: the Otana is the Player Character's personal transport, acivilian freighter, but between the massive shield banks, nigh-impenetrable armour and auto-targeting laser turrets with 360° coverage it went through the series' signature fighters like a mower through grass. The Millenium Falcon was even worse, having all that and a high top speed to boot, but we can kinda forgive that.
Star Wars: Rogue Squadron for the Nintendo 64 had the V-Wing airspeeder. It was fast and agile, possessed a unique rapid-fire feature for its blasters, and a speed booster as standard equipment. Its only initial downside is the secondary cluster missiles, which are dummy rockets that fire in a hexagonal pattern. However, these become a Game Breaker when you find the hidden power-up that makes each cluster rocket an individual seeker missile that can kill just about any TIE in a single hit. Armored targets fell quickly to these missiles as well, considering if all clusters hit a target the resulting damage made a proton torpedo look like a water balloon. Combine this powerful secondary weapon with the agility, speed, and firepower of the V-Wing and you have a very broken fighter.
Diablo's Sorcerer was ridiculously easy to break by using the MS No-Stun bug. The "stun" that occurs if your character (or a monster) gets hit strongly enough is a huge part of the gameplay. But, Mana Shield can potentially cancel that. The problem is that it works by first applying damage to your life (as usual) but then converting it to your mana. If the damage is greater than your life, you're considered DEAD (and not stunned) for milliseconds until Mana Shield does its work. If your life ends up below your level (which is the stun threshold) you can never be stunned when using Mana Shield. Since sorcerers rely on Mana Shield in the normal gameplay anyway, well... To make it even worse, there's an otherwise feared enemy "Black Death" that when hitting you removes 1 of your maximum life, which you could use.
The sequel is much, much worse when it comes to imbalance. A Paladin with the Blessed Hammer / Concentration combo can kill virtually everything in the entire game in seconds with no effort, and the beta 1.13 patch (likely to be the last) has done little to remedy this. It's even worse if they have the Teleport skill from the equally-overpowered Enigma Runeword.
The blood golem iron maiden combo was truly absurd, being a casual gamebreaker rather than requiring players to put 20 points into the same skills to use. The blood golem healed itself and you for some of the damage it dealt. The iron maiden curse caused enemies to damage themselves for a percentage (200% at rank one) of the damage they dealt. The game registered this as the blood golem dealing the damage to them, meaning after just a few ranks it would heal itself and you for much more damage than enemies were dealing. It only worked on physical damage at least, but against that you were both functionally invincible.
Unofficial Expansion PackHellfire's easter egg bard was breakable without any bugs because of dual-wield. Just equip a haste/peril weapon combo together with an undead crown or helm or spirits for life-steal. Because peril does 1x WEAPON damage to the user, but 3x CHARACTER damage to the monsters, and such big life-steal will almost always get your HP back, such a combo can potentially cause total havoc.
In Gotcha Force, the Barrier Girl functions like this against anything that doesn't have a Wave Motion Gun or that can get a decent drilling attack off. Except for drilling attacks (most of which are melee) or really powerful blasters, she can dodge around most shots, only taking a couple of chips to her barrier - by the time it's finally breached, she's probably recharged and can restore the barrier. Even if you have the aforementioned attacks, she's generally fast enough that hitting with those attacks is a pain.
Of course, it gets worse with the Beam Gunner. Fast, possessing a powerful regular ranged attack that recharges quickly, and with a boat of hit points, he can quickly Beam Spam nearly anything to oblivion. If that wasn't enough, he also has a Wave Motion Gun, giving it the ability to even solo against a Combining Mecha.
In Another Century's Episode 2, the Buster Ark possesses an attack called "Riot Shot", essentially a Death Blossom-style "spinningBeam Spam attack, best used when surrounded by enemies. However, due to a programming bug, any enemy that is physically touching the Buster Ark when it activates the move suffers insane damage, potentially allowing the player to one-shot just about everything in the game, even the SNK Bosses they throw at you in Boss Rush mode.
The programmers tried to combat this by making your shield useless while the Biggoron Sword is equipped, but you only need the shield in rare situations. One can equip the Master Sword when the shield is needed and immediately switch back when it isn't. Unlike The Great Fairy Sword, you can also acquire the Biggoron Sword fairly early in the game, as soon as you become an adult.
The Great Fairy Sword in The Legend of Zelda: Majora's Mask is the same weapon in practice, but it comes so late in the game and it's such an unbelievable huge task to get a hold of that most players don't bother with it. Also, when you acquire all of the other masks, you receive the last mask, the Fierce Deity Mask which makes Link so powerful that even the last boss is a joke.
There's the Upgraded Spin Attack for starters. Oh sure, you have to find all 100 Malamais to get it, but it's so ridiculously powerful that it takes down nearly any enemy, boss or mini boss in two hits, has a range about as wide as half the screen and can rip whole hordes of monsters apart in seconds. The minute you get this, the Bonus Dungeon basically loses about half its difficulty, as does anything left in the quest.
The Nice Fire Rod. The upgraded version shoots out a huge pillar of fire with a massive range that can stun lock enemies and push them backwards while doing a ton of damage, and can even hit flying monsters. It can be gotten as early as the fourth dungeon in theory, since you only need to be able to buy it and find just 10 Malamais to upgrade it.
The Nice Ice Rod. Drops four large chunks of ice on enemies, with both a fairly decent range and the bonus of being able to hit things on higher ledges and in the air. Oh, and because it's ice based, enemies get frozen solid upon being hit (with a few exceptions), allowing you to one hit kill them afterwards with any melee or fire based weapon.
The Tornado Rod. It stuns whatever's around you, making it an extremely useful defense against any enemy that primarily attacks by touching you, which is nearly everything in the game. Then you have the Nice Tornado Rod, which increases its range even more.
Just about any Nice item to be honest would probably fit here if used well, since their effects let you just power straight through your enemies with stuff like spreadshots, very quick firing/reloading times and the ability to stun enemies.
Borador, the dwarf rogue from Baldurs Gate 2: Dark Alliance was perhaps the easiest character to solo the entire game with. One of his first skills was a multishot that produced an additional shot from a crossbow at the cost of a little mana. However, the game contained an item enchanting system that allowed you to put up to two special abilities on your weapon, one of which gave you back a fraction of your mana pool on a successful hit. Enchanting a crossbow with this effect, some other enchantment for more damage, and then sinking all other points and money into multishot, armor skills, and hit points netted you the ability to run up into an enemy's face and hold the multishot button and pour crossbow bolts into their carapace until they resembled a dead bloody hedgehog. This held true from everything from two-headed giants to slime creatures to the game's Final Boss; the only creatures it did not work against were those with resistances to piercing damage and trolls; then the answer was either dual-wielding morningstars, or a pinch of fire or acid, respectively.
The save system used in both Dark Alliance games was another Game Breaker: It was very simple and easy to abuse the "import character" options to essentially get unlimited funds and experience in just a few minutes.
Splinter Cell: Conviction has the Five-Seven, a silenced pistol made available to you very early on in the game. It has the biggest magazine size of any of the pistols, improved accuracy and (once you add only one upgrade) gives you the ability to execute four enemies at once with the "mark and execute" system (the highest you can perform at once). If you're a decent stealth player, there's little reason to use any other weapon besides it, as you can effectively take down a squad of enemies in seconds.
Once unlocked, you can also use it in any mission except the first, but if you somehow need a higher-capacity magazine, the pretty-much-best Alternate Weapon is the MP7A1 machine pistol — suppressed by default, able to be upgraded to have three marks (and hence to commit three executions), about 33% more damage (if you even have to fire normally), and have its magazine size doubled from 20 to 40 rounds. Moreover, since it's a machine pistol the user can wield it while holding a human shield or onto a pipe or ledge. Finally, due to alternate weapons' "three magazines' worth of spare ammo" accounting for Extended Magazine upgrades, that means that the MP7A1 with Extended Magazine goes from 20/60 (80 rounds total) to 40/120 (160 rounds total) — most of the assault rifles and submachine guns have only 30/90 (120 rounds total).
Biggest gamebreaker though are the multipliers. The first one is usually quite expensive (half a million or more, and usually you need to have beaten most of the story before you can actually buy it), and merely doubles your income. This alone however makes getting True Jedi/Pirate/Archeologist/Wizard/Whatever in any level a doddle. But then the next one costs double the price, but with a x2 multiplier it's just a case of collecting the same amount again. The thing is, with these multipliers, is that they stack. x2 and x4 becomes x8. You can get x2, x4, x6, x8 and x10, or a multiplier of 3,840, making the lowest possible stud worth 38,400. By the time you've got the first two, you'll earn enough for the third without even trying, even though it costs ridiculous money. Get them all, and maxing out the money count can happen in minutes, giving you enough money to buy anything else.
Streets of Rage 2 has Axel's Grand Upper special. A brief introduction; all four player characters have three main special moves; standing-A, a power attack that slightly reduces your health if it hits, forward-A, a strong attack that decreases your health regardless of whether it hits or not, and forward-forward-B, a special that doesn't harm you. The problem? Axel's Grand Upper is his forward-forward-B, and is more powerful than his or anyone else's forward-A move. Axel is invincible for the entire animation (it can be used to slide straight through projectiles and attack bikers without jumping over their bikes), it scores a hit on every single frame, hits anyone who touches Axel's sprite from any direction at any time, and slides forward until Axel hits something if he does it away from someone. About the only enemies who can deal with it are those with long counter-moves that can wait it out (so that'd be the bosses Abadede, R. Bear, and absolutely nobody else), Shiva (who had roughly the same attack with the slide run out to most of the screen) and Mr. X.
Scarface: The World is Yours. The Bodog jeep with the machine gun on top? Makes the required 'Tony versus a crowd of mooks' fights terrifically easy. Especially if one is in an out of the way spot; the cops have trouble finding those.
From Battlestations Midway we have Torpedo Bombers and Torpedoes themselves. They can sink an enemy ship faster than Dive Bombers and even full on barrages of main guns from Destroyers, Cruisers, and even Battleships.
In the arcade version of Double Dragon, almost all of the enemies can be easily defeated by having the player turn his back and use the elbow attack (punch and jump simultaneously) on them. This is because enemy characters are normally hesitant to approach the player upfront, but are more than willing to attack from behind. The elbow attack has a wide range and knocks an enemy in one hit, the same effect as doing an uppercut or roundhouse kick, yet it's easier to perform and no matter how much the player abuses this technique, the enemy's A.I. doesn't bother to change its pattern. The elbow punch was considerably nerfed in most of the sequels and home versions, if not outright removed.
In the Flash game Great Dungeon in the Sky, you can basically sweep the whole game with any character with the Summon Creature ability. Because enemies don't notice you unless you're on the same level as them, if you find a nice place to stand, you can just keep dropping monsters on them until they're dead. And one of the starting classes has it. For added amusement, unlock the Wind or Platinum Dragon: no need for a place to stand now, just hover in the air and summon baby dragons/skeletons until everything else in the room is dead.
Said starting class, the Necromance, is also a Game Breaker in its own right thanks to having a fast ranged attack and a fast healing spell.
Metal Gear Solid: The Twin Snakes was the updated version of the original MGS for the GameCube, graphically enhancing the maps and adding the new game-play additions from MGS 2. The problem is that it has carried the narrow layout stages and limited number of enemies from the limitations of the PlayStation original. The new game-play features like first person mode allow you to pick off from a distance guards and security cameras once you have the silence pistol which has no range. Making the game a walkover.
In Metal Gear Solid 3: Snake Eater3D, the Photo Camo feature, which lets you create camouflage from pictures taken with the 3DS' cameras, can generate camouflages that grant a 100% Camo Index, normally only obtainable with the Stealth Camouflage item only available in a New Game+, or the Moss Camo, obtained by holding up The End.
Metal Gear Solid 4 has the M14EBR. In gameplay terms, it's essentially a cross between an assault rifle and a sniper rifle, with none of the drawbacks of either (it can be switched between an accurate semi-auto mode and a fast full-auto mode at will). It's also upgradeable, almost eliminating any disadvantages of using it at close range or in third-person mode. You can get this weapon very early in the game, before any setpiece battles, and with a fairly easy and short sidequest, you can get it for free.
The Game Boy AdvanceShaman King Master of Spirits has Black Raven, Michael, and Golem. To put it simply, Black Raven increase Spirit regeneration which allowed you to use more Spirit attacks which is essential on the game to deal higher damage. Michael and Golem are, in a simple term a splitted version of Amidamaru's Antiquity upgrade, which unleash a BFS that cuts 235 deegree and can hit walls, instead, Michael is a fast middle range projectlie that can goes through wall. Golem fires full screen a fast Laser beam that hits 180 deegree of the screen, but did not past the wall. Both of these atack consumes way less energy than Amidamaru's Antiquity upgrade, and deals respectable damage on its own right that match the likes of said upgrade and Matamune. The use of Golem and Michael renders the final level a total joke(that is if you can beat Golem) and made both the Big Bad and the Final Boss of the first game a joke. While still broken in the second game, the Final Boss restricts you to only use Amidamaru as your spirit in the final battle.
There are three Spirits(one of them being combinations) that made the whole game easier to manage :
The first you can obtain is a Combination Attack of 5 passive Status Buff spirits. If you equipped all of them, when you dies, you are taken back to the World Map and gain all of your health unless your fighting a Boss. This allows you to save your money to buy healing items, which you can dedicate to Boss fights and Mid Way of the levels by purposefully killing yourself after each level and started in a Top condition which makes a lot of difference(note that you dont get a health recovery unless you finished a level in this game, and you dont even recover all of your health).
Jen is acquired mid game, and it has an awesome passive effect. For every 50 kills you got, you get a chance to acquire a little bit of money, or an item. The trick is to kill 50 enemy, which you can do by switching screens or going to easy level, and get an item, which you can sell for appropriate item or use them for getting through the level. In other words, by the time you acquired Jen, you would be stocked with money and items that made it easier to win the game.
Last but not least, is the Grand Tao Dragon. simply put, the Grand Tao Dragon allowed you to use it on a finished level, and skip it. While it sounds simple, the ability to skip troublesome levels is ridiculously useful for travelling around for several purposes.
The game Psychic World for the Sega Master System and Game Gear gives you an Invincibility skill that costs a moderate amount of energy to use. It also gives you a move that turns HP into energy at a very favorable exchange rate. By using them together, you can be invulnerable to damage for the entire duration of the game.
In Castle Crashers, the Red Knight (lightning) is this for much of the game. Here's why: his basic magical ability is a sustained lightning bolt. While the bolt is going, any enemy caught in it is paralyzed and continues to take damage. Each point of damage is considered a "hit" and exp is calculated by hit, not by kill. Therefore, using the red knight's magic paralyzes enemies and causes exp to rise faster than any other character in the game, and paralyzes any humanoid type enemy. It is also devastatingly effective against bosses. Until the final level, where the basic enemies are magic proof, this is THE most effective spell available, bar none. Until you reach insane mode, this power is nearly unstoppable.
Dust: An Elysian Tail has Dust's aerial spin combined with Fidget's projectiles. Very few enemies can attack him while he is doing this, the projectiles put enemies into hit stun and knock them into the air (allowing Dust to later attack them to regain magic), and in the endgame it is possible to boost your Fidget stat to ten times its base level, turning it from "killing enemies while not being able to be hurt" to "very quickly killing enemies while not being able to be hurt." Worse still, the few enemies who can knock you out of it are STILL best dealt with by projectile spam, to put them in hitstun so they can't attack you. The only enemy in the game who cannot be killed in this way is an enemy you must counter the attack of to damage, and they are rare and almost always encountered on their own, and easily bypassed anyway. Oh, and the aerial spin tracks enemies too, and can boost you very high into the air, allowing for Sequence Skipping at times as well.
The beat 'em up River City Ransom has the books "Stone Hands", "Dragon Feet", and "Grand Slam". Once you accumulate enough money to buy at least one, the game becomes stupidly easy, as these books make your fist, kick, or weapon attacks three times faster. This allows you to easily beat any enemy with no chance of them retaliating. Especially with the "Grand Slam" (affects weapon attacks), since some weapons have a quite long range, so you can beat anyone without them even getting close to you.
Zombies Ate My Neighbors has the fire extingushier, which can freeze enemies in place. On paper, it stinks, but if you keep squirting an enemy with it, it can freeze them in place for long enough for you to cycle to the watergun and kill them.