Einhänder has the Flash Weapon Pod, which shoots out a deadly pink laser that hurts A LOT but is very rare to find and has very little ammunition. Combine that with the Secret Character Astraea Mk II, who starts out each life with 9999 ammunition for each weapon, give it two Flash pods as its starting weapons, and you'll tear up pretty much everything in the game.
Fire Shark has the flamethrower weapon◊. At maximum level, it fires out SIX streams of deadly fire in a spread (initially). The 4 side flames then proceed to sweep the sides AND back of the player, decimating most mooks they touch via massive damage. Not only that, it's the only weapon to hit behind the player character (there WILL be enemies coming from behind at times). Small wonder why the game is called FIRE Shark...
The hidden Slave fighter in Raiden Fighters. It fires shots that spread out in front of it, which fire very fast and are capable of doing large amounts of damage, particularly at point blank. Moreover, it has a small hitbox, and if you choose the Judge Spear variation of the Slave, you not only can move absurdly fast, but you also have the Judge Spear's super-powerful bomb. The Slave is so hideously broken that all the other ships are simply not worth using; on the Raiden Fighters Aces compilation, the Slave dominates every single online leaderboard, save for ship-specific leaderboards.
Some consider the Judge Spear itself to be a Game Breaker. Fully power it up and give it a Slave formation that makes up for its lack of defensive spread, and you can easily tear through large enemies (and earn QUICK SHOT! bonuses that most other ships would find impossible to earn) and bring down bosses in very little time.
JustifiedGame Breaker of sorts: The Boundary Team in Touhou: Imperishable Night is by and far the easiest of the teams to beat the game with, with their homing attacks, smaller hitbox, and extremely long deathbomb timer (which was already quite long for a Touhou game to begin with). The characters that make up the team? The main character of the series, and the second Bonus Level Of Hell's boss from the previous game that can control boundaries (Read: Able to manipulate damn near anything she pleases, be it Dream and Reality, Motion and Stillness, Life and Death, or pretty much anything that could be conceived of as having a boundary whether or not it makes sense in real life.), is older than Gensokyo itself, and has a very capable shikigami to help with her attacks. Yes, the plot power there is as great as implied.
Also from Imperishable Night is the "Malice Cannon" glitch. When using the Magic Team, pressing the Shift button on and off every half second or so has the effect of both Marisa and Alice's shots staying on screen at the same time, resulting in the "Malice Cannon," which inflicts the most amount of damage on the opposition in the entire game. Despite this, the Magic Team is still the weakest team (or at least the hardest to use) due to being completely unable to attack anything that isn't directly in front.
Perfect Cherry Blossom brings in Sakuya as a playable character, and she is, by and large, one of the easier characters to clear the game with; her normal shot covers the screen, while her focused shot locks in on enemies, and her bombs (depending on the shot type) have some of the longer invincibility times in the game. And she gets four per life, compared to Reimu's three and Marisa's paltry two.
There's an inversion because of the bombs, though; there are bosses on the extra stages who get invincibility frames during their Spell Cards as soon as you bomb. Declaring bombs actually stalls the card, making it harder than it should be, so it's actually better to reserve the bomb stock to activate your border of life and death counter. As game breaker as Sakuya can be in the normal game, it's harder to beat the extra stages with her than with Reimu, whose shots home at sharper angles, has a smaller hitbox and gets a longer time frame to activate her counter-death move.
Phantasmagoria of Flower View: Medicine Melancholy's "Sweet Poison" card is an immovable poison cloud that can slow down opponents; when pitted against the computer, the AI is programmed to duck around enemy shots, so throwing out several of these shots in their path will result in some... interesting situations.
Eiki Shiki's boss summon Spell Card also has some odd effects on the AI. The AI appears to not think ahead more than a split-second, while Eiki's summoned boss image regularly shoots a wide laser aimed directly at the opponent, leaving them about a second to get out of the way. Clearly, this is longer than the amount of time the AI tries to think ahead, since it will very often fail to move out of the way.
Similarly, Aya Shameimaru's meteors make the AI look like an idiot, since by the time the meteor enters the area the computer can "see", it's usually too late for it to dodge. See here for an example of this in action, and note that this is done on Lunatic difficulty, in which the AI can sometimes last over ten minutes against normal characters. Helping Aya's case even more is that this game's story mode lacks Mirror Matches, and Aya is That One Boss.
That is mainly because the A.I. in this game works better with faster characters. You will see the difference if you do a little test and see how long can Yuuka last in comparison to Aya.
The 'Marisa Bugged/Broken' glitch from Mountain of Faith. Put simply, due to a mishap in the game programming Marisa B does absurd damage firing unfocused between 3 and 4 power. By absurd damage, I mean killing bosses before their bullets even approach Marisa. If you can get through the stages with a decent amount of power this makes clearing the game an absolute joke. The reason this is going here is that if it's an accidental glitch you would expect a patch - the game's been out for over three years now, and no fix.
Mountain of Faith in general is broken by its bomb system. Because your bombs are tied to your power level, and because there is an extra level of power (5.00 power is functionally the same thing as 4.00 power, except that power items stop appearing, making it basically a free bomb), as long as you never hit max there will be more than enough power items to make it through virtually anything. The bombs are very large, very powerful, and grant both autocollection and invincibility throughout without any real downsides besides the power drop. To prove the point, there is an infamous replay in which the player bombs every attack and still beats the game without continues.
MarisaA in Lotus Land Story epitomizes this. Apart from the Good Bad Bugs listed above (and in the case of the "Malice Cannon", even then), MarisaA in Lotus Land Story is considered to be the most overpowered shot type to exist in any Touhou game, purely by virtue of how absurdly powerful her lasers are. It is not an exaggeration to say that she ends boss attacks 60% faster than the next most powerful shot type. On top of that, her lasers pierce enemies, are the only shot in the game that does, and there will be enemies hiding behind other enemies regularly throughout the game. Considering this, it's no wonder ZUN has been so reluctant to give Marisa's laser shot types in later games any amount of stand-out power.
There's also MarisaB from Double Dealing Character. The game has a system where when you autocollect point or power items (whether by bombing or by using the auto-collect point at the top of the screen), it rewards you based on how many items you collected - 60+ items guarantees you a life piece, 3 of which make an extra life. This normally works fine, since you won't see 60+ items in one place very often. But MarisaB's bomb converts any bullets it hits into power items, which add to the collection total and make it ridiculously easy to gain lives by simply throwing the bomb into dense areas - and remember, just bombing causes an autocollect by itself, triggering another bonus. See here for this in action. It helps that even apart from this sort of abuse, MarisaB has the highest raw power of any shot type in the game - and because of the power items spawned from the bombs, she will basically always be at full power.
Even Touhou's best fangames are not immune to this, as ReimuA in the popular Touhou fangame Marine Benefit shows us. At first glance, she appears to be a basic forward-focus needles shot with a rather bad bomb to make up for the power of her shot - the bomb doesn't even hit the boss at all, only clearing the area directly around Reimu when the bomb button is pressed, and not moving to where Reimu moves during its duration. But this ignores one important thing about how the game works: in Marine Benefit, grazing increases the oxygen counter, which is what gives the player extra lives. Instead of the bomb being ReimuA's weakness, it's actually a godsend. Every time the player bombs, rushing up to the boss and grazing everything they shoot during the invincibility period can give the player a ridiculous amount of resources. For some idea of just how bad this can get, see here, where a player ends an attack with double the resources they came in with...despite dying six times, and making multiple mistakes. Or here, in which that same player demonstrates that it's a constant issue throughout the game, instead of just being the fault of that one attack.
Tyrian has the Plasma Storm, a "sidekick" weapon that has limited ammo (although it regenerates slowly) but does massive damage and has a very fast fire rate - you can empty it's ten shots in about a second, which will easily wipe out anything that's not invulnerable. Oh, and it's available before the first level. You can only afford one of two, but that's enough. It was toned down slightly in Tyrian 2000, but still retains most of its original awesomeness.
Also, the Zica Flamethrower, a "sidekick" that fires a stream of flame that passes through enemies, allows one to "affect" an enemy that has a collision box, and then ram their ship into said enemy and One-Hit Kill them. This also includes almost any boss that is not invulnerable at the time. (This Game Breaker applies to any weapon with a penetration effect.)
Not a weapon-type Game Breaker, but something of note is that during Episode I, in Savara V, during the boss fight, you can stay in a spot away from the boss and intercept its shots for money. The best part? The bosses never have a time limit, so you can do this for as long as you like for bottomless amounts of money.
The Spread Gun in Contra. Since it fires five shots at a time, you can destroy quite a few bosses with ease just by firing point-blank. And most other enemies only need one shot anyway. If you're a component platform player, the jig is up once you have this weapon.
The Fire Gun in Contra III constantly does high damage to anything in the fire. Most bosses die in seconds if you aim it at their weak spots. Also the Laser Gun, which fires at a slow rate but also pierces through many enemies and kills bosses faster.
The upgraded version of the Machine Gun in Super Contra (the arcade version, not the NES game Super C) has a ridiculously fast firing rate allows you to wipe out most bosses in a matter of seconds
Browny in Hard Corps. He is very small, is the only character with a double jump and his Super-Electromagnetic Yo-Yo weapon can destroy bosses very quickly. He has the worst slide but that's a very minor drawback compared to his other advantages.
Brad Fang is also very overpowered. His A-type weapon, the Beast Shot, has a wider range than the other characters' A-type weapons, and his Explosive Punch and Psycho Blaster can wipe out bosses in seconds. His only drawback is that his tall stature makes his an easier target than the other characters, and the latter two weapons can only be fired horizontally.
Weapon Set F in Neo Contra has the GV Laser (from Gradius V nonetheless, hence the name), which fires a constant laser beam with a ridiculously long range. Its the best weapon to use if you want an easy S-rank in no time.
The troper writing this would like to point out weapon set D. The main weapon is a Lightning Gun that can One-Hit Kill many enemies, the secondary is a hard hitting bazooka that does massive damage against bosses and stationary objects, and the lock-on weapon is the Heaven'sLaser, which is absurdly strong, never misses, and reloads stupidly fast, making things that need a lock-on utter push-overs. Oh, and it's unlocked early on at Stage 5, compared to Weapon Set F's Stage 7 requirement.
Gunstar Heroes has one of two game-breakers depending on your movement choice at the beginning of the game. If you chose "free shot" (i.e., move while firing), your best option is the Lightning/Chaser combo, which fires a large homing laser that stays onscreen and seeks out any targets as long as you hold the fire button. It makes many situations much easier, in that you can focus entirely on dodging enemy attacks while letting it do its thing. It's kinda stupid, though, in that it's nigh-impossible to force the weapon to attack a particular target, and it may just end up trying to destroy something that's indestructible; its damage output is also rather lacking. On the opposite end of the spectrum, if you chose "fixed shot" controls (i.e., holding the fire button makes your character unable to run, which has the side-effect of aiming diagonally much easier), use Lightning/Fire instead. It's essentially a short-range beam of energy that's extremely powerful and can even destroy most enemy bullets. Which one ends up breaking your game largely depends on your playing style, but most vets will conclude that Lightning/Fire is superior despite its terrible range that often puts the player right in the face of danger (contending, of course, that the high damage and bullet-killing properties made close-range encounters end in a snap).
In Thunder Force VI, every ship is broken in some way. The starting ship, the Phoenix, starts with all of its weapons and both Craws, and never loses them on dying like ships from past games. The Rynex-R, unlocked upon completing the game once, doesn't have this luxury, but more than makes up for it with the incredibly broken Twin Shot Over Weapon, pictured above. The caption is not hyperbole; a boss that takes 30-60 seconds to defeat can easily go down in under 10 seconds. It also has the Free Way weapon, which will target and slam an enemy that comes within proximity of your ship, making it idea for crowded parts of the game. Finally, the Syrinx, the last unlockable ship, is similar to the Phoenix, but with a new Wave Shot that, instead of firing a three-way spread of crescent wave bursts, fires a microwave-style laser that incinerates everything in its path and makes waves of "popcorn" enemies all but trivial.
Thunder Force III / Thunder Force AC / Thunder Spirits: Grab a Saber powerup. Use it on a boss. Instant win.
Thunder Force V: Grab a Free Range powerup. Get up close to a boss and spam its Over Weapon. Instant win and x16 point multiplier. Heck, the Free Range in general. It projects a wireframe cone in a direction of the player's choosing, and anything that gets inside is fried by a powerful 100% accurate laser, even more if the player has CRAWs.
In the case of Thunder Force V, for owners of the Playstation version, they had access to the RVR-01HiS via a secret method. This version of the RVR-01 was significantly faster and boasted slightly improved firepower. The only downside is reduced CRAW regeneration, but when they appear as random item drops, who needs to worry about CRAW recharge rate?
R-Type Final has the Needle Force, which comes with the otherwise unspectacular Pod ships. It's not especially powerful when docked, but once it's loose a fully-powered Needle Force will fire a spray of bullets in all 32 directions possible for bullets to travel in a spinning pattern, one bullet per game tick. No other Force fires even close to this fast and no other force is capable of filling the screen so effectively with bullets. Park it next to a boss's Weak Point and said boss will go down in very little time. The space armada in level 5? No problem - just launch the Force into each ship as it arrives and wait for it to do its magic. They will hardly be able to get a single shot off before they are destroyed, one after the other.
Also the Mega Wave Cannon, the little brother of the intentionally broke Giga Wave Cannon. Why? Due to the way things work, the Mega is just as good at killing everything as the Giga regardless of how many loops. Note: this is a Wave Cannon that basically one shots anything that's not explicitly invincible AND goes through walls and obstacles.
The Lock-on Laser in Raiden II. They removed it in Raiden III, but restored it by popular demand in Raiden IV.
The Lock-on Laser is actually the weakest weapon in the game, most players go with the Spread Shot or the laser.
Falchion Beta in Gradius Gaiden, compared to the other three ships Lord British, Vic Viper, and Jade Knight. For its Double, Falchion Beta has Auto-Aim - Which auto-tracks and destroys any enemies above it. Auto-Aim renders any stage a cakewalk, even in higher loops. Its Laser, Gravity Bullet, causes such a high amount of concentrated damage that bosses die in mere seconds. Its missile weapon, Rolling Missile, will also pierce targets forward and back from where it drops.
From Gradius III, we have the Reduce shield, which reduces your ship's size and hitbox. In the arcade version, it provides no defense, but in the SNES port, it becomes a two-hit hitbox-reducing Force Field (though the first hit makes you grow slightly closer back to normal size), so not only do you become a smaller target, you also get reasonable defense to go with it. What propels it into game breaker territory outright is Full Barrier, a !-slot powerup that restores a partially-damaged shield back to full. So after activating Reduce, simply highlight the ! slot so if you take damage, you can keep your ship at minimum size without having to deplete your shield first.
The Thunder Claw and Binchou Laser in Twin Cobra II. The red and blue weapons needs ungodly Button Mashing to make them not piss-weak, whereas the Thunder Claw has an huge spread and doesn't need rapid fire to be powerful. The Binchou Laser doesn't need Button Mashing either and it kill things really fast.
The auto-bomb feature, which substitutes a life lost for a bomb fired (if any are left) if you get hit. Games that implement this become much easier, as your bombs are essentially extra lives and you don't need to concern yourself with deciding in a sticky situation whether to use up a bomb. Take Mushihime-sama Futari's Novice mode, which has auto-bomb, for instance. You start with 3 lives and 3 bombs, and every time you die you reset to 3 bombs. 3 lives × 3 automatically-fired bombs = what is essentially 9 lives, which you can get 1 more of by getting a bomb and 3 more of by getting a 1-Up. DoDonPachi Dai-Fukkatsu Ver. 1.5 also has (non-disableable) auto-bomb, which contributes to Dai-Fukkatsu being regarded as the easiest DonPachi game to complete one loop of.
Some games, however, are smart about this. Ketsui Death Label has auto-bomb, but when it is activated, you lose all of your bombs.
The X-Wing series is fond of these:
X-Wing gave us the B-wing.
TIE Fighter gave us the TIE Defender and Missile Boat. The former is better than any other ship available before it either game at everything besides carrying the most ordnance, which it was still good at. It was faster than the A-Wing and Tie Interceptor, better shields than the Y-Wing and B-Wing, four laser cannons, ion cannons, and could carry a good set of missiles. The latter was well shielded and fast, not as much as the TIE Defender, it could carry WAY more missiles than anything else and had the ability to use a temporary boost that doubled its speed, making it the fastest ship in the game, and it carried so many missiles it could just rely on them exclusively.
X-Wing vs. TIE Fighter gave us the rule that you could use any Rebel craft on any Rebel mission and any Imperial craft on any Imperial mission. And you could use the TIE Defender, B-wing, TIE Avenger (called TIE Advanced for some reason), and Assault Gunboat. Yeah.
Freighters like the YT-1300 have turrets, completely negating the maneuverability advantage of unshielded Imperial craft. A pair of these can wipe out dozens of Tie Fighters in a single battle.
DeathSmiles Mega Black Label has Sakura. All the other characters in the game have a single familiar, which fires alongside them and absorbs suicide bullets. Sakura has two familiars, grouped together closely enough that the space between them registers as the hitbox for absorbing suicide bullets. This makes dealing with suicide bullets much easier as Sakura effectively has a single giant familiar.
This is sort of justified, as fighting Bloody Jitterbug requires completing every level on the hardest difficulty without getting hit once. She needs that extra protection.
DoDonPachi DaiFukkatsu has Strong Style, which is essentially a beefed up version of Bomb Style. Compared to Strong Style, Bomb Style is utterly useless. Hence why in DaiFukkatsu BLACK LABEL, selecting Strong Style will sharply increase enemy difficulty, essentially turning Strong Style into the rough equivalent of Mushihime-sama's Ultra Mode.
Strikers 1945 II brings the world the F5-U Flying Pancake and the Hayate. The F5-U isn't strong but the main gun spreads a little, has homing lasers, and it's quick enough to evade many attacks in the game. Also, its charge shot consists of a laser that can kill many enemies in little to no time. The Hayate isn't as fast, but compensates for its lethality via attack drones that home in and whittle enemies down to nothing.
Then there's the P-55 Ascender, unlocked via cheat code. Again, not the fastest, but compensats for it with its decent strength and ludicrous special attack. It homes in on enemies, charges quickly and can hold the maximum nine specials—when other planes have at the most five specials.
Time Crisis: Crisis Zone has the Laser Rifle. While exclusive to the console port, it is the most broken weapon in the game. Instantaneous hit rate, obscene rate of fire, very damaging, and it takes no effort to kill anything. The only issue is that it has to be unlocked, but it is well worth it. The weapon in question can be seen here.
In the mobile game Gun Bros. by Glu, there is the obscenely powerful heavy gun called the Kraken. When shot, it shoots loads of homing missiles. As you shoot, the gun appears to quickly overheat. All is lost until...wait...it shoots a gigantic laser beam that vaporizes anything it touches. The gun does not stop firing missiles even WHILE firing the laser. However, there is a price to pay. Quite literally. Originally when the gun was released it was 1400 War Bucks. (currency you spend real cash on.) The maximum package currently offered is 710 War Bucks for $99.99. Which means this thing was initially a little over $200. If you thought that was bad, they've updated it to cost a staggering 3499 War Bucks. Do the math...yeah. Holy shit indeed.
Bullet Heaven has Anna, unlockable by getting S-ranks on five levels. All the other player characters have subweapons that are, well, weapons; a wider-range, more powerful attack that can only be used occasionally. Anna's subweapon, however, is a Super Mode that gives her triple firepower until the subweapon meter runs down. Upgrade the subweapon recharge speed to max, and you can pretty much keep it on permanently.
FreeSpace 2 has the Trebuchet, presented in-game as an anti-bomber missile with an effective range of 5000 meters. However, it does extremeSub System Damage, more even than the Stiletto II (which is actually designed to take out subsystems, much slower than the Trebuchet, and vulnerable to being shot down), and no anti-fighter capship weapons can reach even close to five kilometers. This basically allows you to disarm capital ships with impunity with no chance of the target ship retaliating or destroying your incoming warheads.
The "Field" ship, the sixth unlockable ship, has a circle that it uses to target enemies; anything that enters the circle will be zapped with lasers until they leave the circle or die. Said circle gets wider the more you power it up, until its diameter becomes the size of the whole screen. At this point, anything that dies in one shot will not be able to touch you. Bosses still take some time to be killed, but if you shrink your circle by half the attack will do extra damage.
The "Variable" ship, which uses four Attack Drones to wield laser swords that inflict immense damage, and can be swung by moving up and down. By powering up the weapon and moving the swords such that they all intersect, you can easily eat bosses' health for breakfast. The Variable ship is also great as a defensive weapon; you can move the swords to cover the area right in front of you; certain enemy shots as well as most enemies will be destroyed trying to get to you.
In the Adobe FlashWeb GameEnigmata 2: Genu's Revenge, the Stop Time skill is this. It stops time, allowing you to wail on a boss without much problem, and you can activate it again as long as you have energy remaining. It has a high energy cost... which can by solved by upgrading it so that it uses less energy.
The "INFINITE Bonus" equipment. Normally, when you get a bonus weapon, it only lasts for a short time before reverting back to your regular weapon. This powerup makes your bonuses last infinitely. Combine with the "Bonus Lock" skill to prevent Power Up Letdown, and you have a monster ship on your hands.