Any FPS that forgets to assign a maximum fire rate to one or more semi-automatic weapons. None are more blatant than the original Red Faction's pistol. Killing another player from full health and full armor in 200ms flat with the very weapon you spawn with... yeah.
Halo's plasma pistol. In addition to firing a powerful, homing charge-up shot (see more info below), players with rapid-twitch reflexes could fire off regular shots at an extremely high rate, even faster than the Plasma Rifle, in a Death of a Thousand Cuts fashion. Was altered in subsequent games.
However, the "rapid-twitch" came back (sort of?) in Reach, and could be shot even faster. It was practically a sub-automatic weapon.
Otherwise entirely forgettable game Gore had the pistol working like this, which could make it preferable to the machine gun.
Any hitscan pistol with no accuracy error is effectively a Sniper Pistol.
A number of semi-automatic rifles in the Call of Duty series fall prey to this, with the weapons having no or so little recoil that console players could use "modded" controllers to press the trigger inhumanly fast and PC players could bind fire to their mouse wheel, instantly emptying the magazine and killing any player they're aiming at. Call of Duty: Black Ops fixed it especially sneakily by causing the rifles to jam if they fire too fast.
In Combat Arms, the Ninjato, the G36E, the L96A1, the Desert Eagle, and the Anaconda, just to name a few. The nut shot was considered this so much that the European version of the game voted to remove it from their version and it's been nerfed for the other versions.
Mei's mod MP7. The 3 shot stopping power of the AK-47, without any such silly thing as recoil, with high mobility and nearly as accurate as an assault rifle. Pray you have never had the misfortune of playing against someone with one of these beauties. Also, specialists in general are broken. Viper, in particular, is very fast, which, when combined with a small, buggy hitbox (and outright immunity to nutshots), that makes her very difficult to kill while bunnyhopping, which all of them inevitably do. Finally, the M32, which is exactly like the grenade launcher from Call of Duty, except with SIX rounds. The use of the latter two will get you kicked from roughly half the servers you play on.
Specialists are supposed to be "balanced" in that anyone of a certain rank can access them for in-game currency. Except that every piece of their gear (and the specialists themselves) are limited by ranks of increasing order (starting from Master Sargent to Lieutenant) and requires an insane amount of GP given the very limited amount of time you can use them. Or you can screw the rules and spend money, which allows you to bypass most if not all rank restrictions (they get much lower) on all the gear and characters, get increased amount of EXP (up to 40%), and even straight up buying GP (with a chance to win 1 million GP, which is more than any player will ever see in their Combat Arms career), getting at least the equivalent of 3-4 games worth in a fraction of the time. Also, the M32 is actually the least broken of the specialist gear.
The Accuracy International AWP in Counter-Strike. Almost all guns in CS take a certain amount of time to kill a target. The only weapons that can truly kill instantly with an unaimed shot are the pump action shotgun from very close ranges, and the knife when backstabbing. The AWP can kill instantly with an unaimed shot at any range whatsoever. There are other sniper rifles, but for those, only headshots are instantly fatal. It was considered to be a complete Game Breaker because of its sheer power, and as a result, the weapon was Nerfed countless times: the telescopic sight was given a black vignette to reduce the field of view, its power was reduced, its accuracy when standing still was also reduced, and people still think it's a Game Breaker...
In the Original mod, there was also the riot shield, a CT specific equipable that when activated, shielded the user from any and all fire coming toward them, the only weak spot was the users feet. Furthermore, while it was supposed to only be useable with a pistol, hacks made it possible to use larger weapons with it. Next to the AWP, it was the most banned item in the original Counter-Strike.
The automatic snipers used to be joke weapons - they were very expensive, heavy, inaccurate and lacked punch. However, an update greatly reduced their recoil and buffed their damage. Now, unless your opponent has lots of backup or is a crack shot with fast reflexes, they don't stand a chance. It is just as heavily banned as the AWP.
One of the limiting factors on all the sniper rifles - the lack of crosshairs , forcing you to use the scope for aimed shots - was also rather easily countered. Some players just marked the crosshairs when they were visible with anything they could think of (small bits of dampened paper, a snip of tape or sticker, making a small smudge, etc.), and they had an instant low-tech solution to the lack of crosshairs.
Half-Life had the crossbow, which essentially was a one-hit kill weapon. The Expansion PackOpposing Force featured a sniper rifle that was pretty much a replacement. While they were great in the single player campaign, they were also available in multiplayer matches (where crossbow was changed to hitscan).
A bigger Game Breaker is the MP5's grenade launcher from the first game. It can kill everything with one shot and, unlike the crossbow, you don't even have to shoot too accurately.
Crossbow isn't too bad in Half-Life 2. The bolt takes a while to get there, so anyone skilled at zigzagging and reversing directions quickly will render the crossbow almost completely ineffectual at medium to long range, barring a lucky shot. Also, it only does 100 points of damage, which means someone with full health and at least 1 armor point (fairly common on most maps) will easily survive a crossbow hit.
The real game breaker in HL2: Deathmatch is the magnum. You can fire 6 fairly rapid shots before reloading, as opposed to the crossbow's 1 shot. The hit is instantaneous, making long-range sniping vastly more effective. It deals 75 points of damage, which means against anyone with 1-50 suit its strength is effectively the exact same as the crossbow's. And to top it all off, while headshots with a crossbow are impossible, a headshot with a magnum will kill anyone, even if they have full health and 200+ suit. It's the most powerful—and probably most often used—weapon in Deathmatch, and for a number of very good reasons.
Also, just to make the magnum even more ludicrous, you can simulate the crossbow's scope via a trick utilizing the standard suit zoom available with any weapon.
The laser sight in Deus Ex can be seen as a bit of a game breaker. Attach it to your weapon and it basically eliminates inaccuracy, meaning the bullet will always hit directly in the centre of the crosshairs even when the target is so far away that the laser dot is practically invisible. Given that the starting pistol can achieve one hit kill headshots even with no training, attaching the laser sight to it makes the combat ridiculously easy. This problem was fixed with the Shifter mod, which made the laser account for your character's hand sway, meaning you could no longer assume the laser was in the centre of the crosshairs and had to be able to see the dot to be able to shoot accurately.
Speaking of Deus Ex: max out the Rifles skill and the shotgun loses the spread effect. All the power of a shotgun blast, all the range of a sniper rifle.
The Dragon Tooth Sword is effective even with no skill points in melee - it's silent, it kills in one hit, it's easily obtainable rather early in the game, since it glows it can be used as an impromptu flashlight rather than wasting bioelectric energy, and with some skill in melee weapons you can break doors with it instead of having to look for a key.
The tradition of game-breaking upgrades continues in Deus Ex: Human Revolution with the 10mm Pistol's armor-piercing modification. On its own, the pistol is a reliable, accurate sidearm with fair range and one-shot takedowns for lightly-armoured enemies. With the upgrade, Heavies are two-shot kills. At the most. And it can be obtained very early in the game, in a location you can't possibly avoid going to, with a code that's very easily obtained.
Likewise, the Typhoon augmentation turns almost every boss battle into cakewalks.
In Red Faction, aside from the pistol, its infamous rail driver is a sniper rifle with quite abundant ammo (it can hold eleven rounds and almost every group of mercenaries has someone with it), instantly kills whoever you hit (even the final boss if she's without her shield), and can both see and shoot through walls.
The GoldenEye engine has some weird quirks, of which the most broken is how explosions work. Seemingly, rather than just assign an AoE of flat damage, the explosions are a series of concentric damage rings; trouble is, they don't all happen at once. Instead, the explosion is a very protracted damage source which is vastly larger than the explosion effect itself. Add to this that walls in the engine don't obstruct splash damage, that explosions are one of the most powerful damage dealers, that explosions both stunlock the player and shove them backwards, and that they kill any normal enemy who touches the blast area at all, and you have a recipe for lots of exploits and / or swearing. Explosives are basically unplayable in Licence To Kill mode, since they can still be fatal even when the explosion has almost entirely vanished.
In addition, Perfect Dark's bots can't see any kind of trap, so they award the player large numbers of free kills by blundering into mines placed in plain sight. And the developers, having fixed none of the explosion mechanics, decided that the game really needed a rapid-fire semi-automatic grenade launcher with a fast reload.
GoldenEye also had Oddjob, who's just short enough that other players had to manually aim down or watch all their shots fly harmlessly straight over his head. Spiritual SuccessorTimeSplitters brought the idea back with The Monkey.... and then with character attributes, made it worse. Half-height character with normal HP and maximum speed? Good luck hitting that.
In addition, there was the RC-P90, based on the real-life FN Herstal P90, which was the most powerful submachine gun in the game. The RC-P90 had practically Bottomless Magazines, and split players over whether having one was cheating or not.
The Farsight XR-20 from Perfect Dark. It sports an X-Ray scope that can see through walls, fires rail beams with infinite penetration, and it tracks your enemies for you. Also: INSTANT DEATH! Oh, you have a shield? Fine, the first shot will just instantly destroy it. Hope you can get across the whole level before your opponent shoots again!
It's also possible to abuse the Poison Knife weapon by throwing it at a player's body before it vanishes. When they respawn, their vision will be horribly blurred, when normally the effect would vanish when they died.
The best part is that if the poison would normally be still in duration when a player dies, it'll be in effect when they respawn. That means you can have half of your life ripped off just for eating a knife when you were next to dead.
Another fun Game Breaker? N-bombs. They can be set to proximity detonation, so just get a couple of boxes of them and toss them all over the level. Your enemies will walk over them and if they don't die, they will be trapped in the blast radius for several seconds, drop their weapons and remain disoriented until the next turn.
A rare single player game breaker in the first level of The World Is Not Enough. Go to the safety deposit room and hit the alarm, which fails the mission. Grab the stuff in the box and run for the door. Mission complete in 15-20 seconds.
Before it was patched to be weaker, the fully upgraded dispersion pistol in Unreal, when used with the power amplifier, could kill any standard enemy in a single shot (including the rock-throwing Mini-Boss; the end boss required only a few more). Even without the power amplifier it was easily one of the most powerful weapons, though it was hard to land hits on rapidly moving targets. The Combat Assault Rifle in Return to Na Pali was similarly overpowered, being the only hitscan weapon without some sort of drawback and allowing the player to use both fire modes at the same time.
The fully upgraded dispersion pistol isn't the only one. Every weapon in Agepack3 and MentalPack1, and some weapons in the Uber2 and Uber4 mods, were HUGE Game Breakers. Mentalpack1's laser minigun shoots lasers and spits out explosive blue shells that will kill Skaarj warriors in one hit. The Flakrifle from the uber2 mod is the Flak Cannon and Shock Rifle crafted into this. It deals one shot kills on any standard enemy and can kill the rock-throwing Mini-Boss in a few hits. The assault rifle from the uber4 mod fires bullets inhumanly fast. The Agemag shoots weird things that will destroy Skaarj and Brutes in a few shots. The military minigun shoots out overpowered bullets and can fire out rockets at will. Even the final boss is a joke with these overpowered weapons.
When a Battlefield 2142 server turns friendly fire off, RDX explosives suddenly become extremely dangerous, since the user can now detonate them even at their feet and walk away with an effortless kill. "RDX hoppers" (because the gamebreakers also rely on bunnyhopping to avoid attacks) are reviled by the community, even by those who occasionally do it.
Much whined about also is the PK-74 rifle rocket attachment and its traditional partner, the Voss light assault rifle. The distinctive 'broop' sound of the rocket firing has lead to Voss / PK users being nicknamed 'broop troops,' and the rocket's large splash area, rapid fire and ability to consistently kill in two hits has caused even more complaining than RDX. The even more powerful triple mortar carried by the APC tends to cause similar amounts of complaints on infantry-heavy maps, as it instantly kills its victims.
And let's not forget the infamous Battlefield Vietnam M60 / LAW kit, which turned US players into Rambo clones with a sniper-accurate machine gun and a portable anti-tank missile. It was soon patched so the machine guns were less accurate and the M60 and LAW belonged to different kits.
Parachutes are unexpectedly effective against aircraft that attempt to roadkill its wearer. The offending aircraft typically explode against the invincible canopy, leaving the wearer only mildly disoriented. Same thing can happen during Titan escapes: an escapee who pulls their cords early will usually murder whoever falls onto him.
There's even more in Battlefield 2:
The US Abrams in Strike at Karkand is often described as unbalancing the map (since the MEC's tanks are at the exact opposite side of the map from where the shooting will invariably start), and the two Chinese jet fighters on Wake Island even more so, to the point that US teams sometimes never get off their carrier at all. Let's not even get started on the fact that the Chinese can drop artillery strikes on the carrier deck.
The air vehicles are near-invincible. Helicopters can take a direct hit from a tank shell, and the only thing that can take down a jet with a semi-competent pilot in it is another jet. The only 2 ground-based AA units are stationary Stinger Sites and AA vehicles. Only a small number of maps have AA vehicles in the first place, they require quite a bit of skill to use (arguably more skill than to fly a jet) and once sighted, they're viciously targeted until destroyed. Stinger Sites are a joke in general, as their range is short, and while you're in 'em, you're a stationary target for bombers. And if the jet is damaged/needs reloading, it can simply FLY OVER THE RUNWAY. It never has any downtime or need to land. Thus it's no surprise that many high-ranking players get their ranks simply because they fly jets constantly, untouchable by most players on the ground... Sadly, nothing has been done whatsoever to deal with this.
In addition, jets demolish the maps. Tanks are slow and have no defense against them, barring a lucky hit from the main cannon (only guaranteed if the pilot is dumb enough to fly directly at the tank from an angle its main gun can reach), so it's all too common to be driving along, and being hit with bombs (one salvo is a kill) before you even heard the jet over your tank's roar. APCs suffer the same problem, but without the one-hit-kill-if-lucky possibility. Mobile AA can kill a jet fast...but only if the jet is distracted, because, as mentioned above, they'll be targeted easily. Jeeps and FAV (Fast attack vehicles) can almost outrun a jet...if you're lucky. And if you're in a fully loaded transport copter, that's six easy kills for a pilot, because those are flying tanks without the armour. Basically, jets are way too overpowered, because they can blow away any vehicle in a single bomb salvo, and any copter, transport or attack, can easily be cut down.
With the way ammo packs work, a team with enough support members can allow their team to continuously throw grenades, forever. Infantry-only matches sometimes boil down to two entire teams throwing grenades at each other over a wall.
In the original release, Blackhawks were overpowered for a number of reasons: First, the minigun was absurdly accurate and could destroy anything that wasn't a tank; second, passengers inside the Blackhawk had access to their tools, so they could repair the Blackhawk while still inside it; and finally, extra people contribute to capturing flags, so a fully loaded chopper could fly in, clear a place out, and capture it within the space of a several seconds. The only thing that could really stop so-called "blackhawk squads" was a jet, and you had to get it on the first pass, otherwise, the engineers on board would just repair all damage, and the imbalance was most apparent on maps without jets. They were however, nerfed into uselessness and obscurity.
For anyone asking, the reason it was impossible to do this for the other helo was it was much slower, less armoured, a bigger target, its guns were crappy machine guns that could barely hurt an infantryman and only 1 player had a position to do in-flight repairs (compared to 2 for the Blackhawk).
The air transport in 2142 carried on this fine tradition.
Another example was the PKM, which, over the course of one patch, went from being a slow firing, but high damaging suppression weapon, to a fast firing sniper rifle with a lot of ammo, requiring another patch to undo the damage done.
There was the issue with AA missiles. Both Stingers and AA missiles on jets were quite inaccurate, then a patch upped the accuracy of missiles to extreme levels. Pilots complained and the stinger missiles were toned down, however jet AA missiles were left alone, turning dog fights from trying to ambush the unsuspecting with the Vulcan gun, into a long game of out turning your opponent (which the Chinese jet always won).
The Sniper class gets Claymores. They're basically anti-infantry landmines that have a sizable 180-degree blast radius. They're for covering your backside while you snipe. In theory. In reality, most Snipers just spawn with them, toss then in a well-traveled area, and proceed to run off and spam grenades. Couple in the fact that the ONLY WAY to get rid of claymores is to set them off and you can see why more snipers get their kills from Claymores and Hand Grenades than legitimate sniping...
The Medic class in general. It can heal itself, revive dead allies, and with unlock weapons, gets one of the highest-damaging, most-accurate guns in the game, the G36E. Compared to the Assault Class, which gets an equally good gun but no heal/revive skills, Medic clearly comes out as the superior class. Battlefield 3 took this to the logical extreme by merging the Assault and Medic classes.
Battlefield 3 has the M16A3/M16A4 (M16A3 being the starting American assault rifle and the last normal Russian assault rifle unlock, the M16A4 is a three-round burst version available to both teams at the same time), which... it's one thing for them to be be the best AR in reload speed, it's another thing when they're basically second best at everything else as well.
The title really goes to the USAS-12, and later the Mk3A1. With frag rounds, it essentially turns the weapon into a handheld IFV cannon with splash damage. Expect users to be called out U Suck At Shooting 12 year-old kid. Eventually this was patched.
Another overpowered shotgun, this time due to a bug, was the underbarrel M26 combined with dart rounds and a heavy barrel on its parent rifle - as of the 1.04 patch, this combination would make each of the twelve flechettes fired by the M26 deal the same damage as a bullet fired from said rifle. Combine with the unlocked-through-coop G3A3, which does more damage than any assault rifle unlocked through actually playing multiplayer, and you dealt enough damage in a single shot to kill someone four times over. In an inversion, the same bug made the above combination with slug rounds nearly unusable except for Cherry Tapping, due to slugs only firing one projectile; the next patch fixed the former but has done nothing for the latter.
Battlefield Play 4 Free has the scout helicopter in Dragon Valley. In theory, its purpose was to harass infantry and quickly deliver small fireteams. Instead, the team who captures B first ends up with a second attack helicopter. Scout helis are the fastest and most maneuverable aircraft in the game, and pack twin miniguns. This allows them to fly over to a firezone and utterly destroy any infantry that gets caught in its crosshairs, all while moving so fast that it makes it damn near impossible to tag it, let alone shoot it down! After the infantry is wiped out, it takes but a few seconds of concentrated fire to eliminate light vehicles, and if you're in a tank the only way to survive is to not be noticed, because there is no way in hell your sluggish crosshairs are catching it while it whittles away at your health.
This video shows how to turn a gunship into an omnidirectional full-auto sniper rifle with almost no recoil, devastating damage and infinite ammo.
Then there is THIS video that teaches players how to convert Blackhawk miniguns into a cheese weapon with "no bullet drop, very limited deviation, unlimited ammunition, and enough stopping power to kill someone more than 350 yards away without sweating." Oh, and it doesn't help that it does spread damage.
A common FPS game breaker well-known in the earlier entries of the aforementioned Battlefield series is Dolphin Diving, a game-exploiting version of the traditional bunnyhopping tactic. This consists of jumping and then hitting the prone key; while the game shows an animation, in reality the player's hitboxes often flatten instantly, making them very difficult to shoot since an opponent must aim for an invisible, lying-down opponent, not what's actually there. Moreover, this often grants the accuracy bonus for being prone, leading to the ridiculous sight of realistic-looking soldiers bouncing around while laid on their chests, firing off perfectly accurate shots. Efforts to destroy this stupidity have met with much resistance from its practitioners, who claim it requires skill, but most modern online FPS games include mechanisms designed to prevent it like sights taking time to 'settle' after changing stance rather than an instant accuracy bonus, or disallowing the player from changing stance while airborne.
Battlefield 2, as mentioned above, is one of the more egregious examples of this. Not only does the hitbox instantly change you to "Prone" while you're in midair, but it also INSTANTLY changes your accuracy to "Prone" while you're in midair. If you were in a dead run and hit the prone key, your accuracy immediately becomes the same as if you'd been prone and aiming for several seconds. Add in the fact that the Support weapons, heavy machine guns that are only accurate from a prone position, are hugely damaging from even long ranges, and you have a serious problem. Users of the PKM, the most powerful and accurate Support weapon, can simply run along until they see an enemy, then immediately tap the prone key and blast away. They're almost more effective than snipers!
The pistol in Halo: Combat Evolved allows for instant-kill headshots. Many players learned to eschew the other weapons (which otherwise are more damaging) in favor of leet pistol skillz. Also, the pistol can take out Hunters in one hit as well, plus, the pistol has a zoom. It was basically a designated marksman's rifle disguised as a handgun.
In addition to the human pistol, the plasma pistol is the best second weapon. The pistol can take down any shield, and the pistol can take out unshielded elites in one hit (headshot). Oh and charged plasma shots are homing.
Leading to the n00b combo. Take out an enemy's shield with the plasma pistol, whip out the regular pistol and Boom, Headshot.
In the PC port, they added the Banshee for multiplayer, complete with a Fuel Rod Gun that flips vehicles and kills infantry with ease. There's also a handheld Fuel Rod Gun that, unlike in later games, was treated as an energy weapon (despite obviously using discrete fuel rods), meaning no lengthy reload times (the only thing balancing the human Rocket Launcher out from the other weapons)!
It did have a lengthy overheat time, but that was generally easy to avoid.
Sarge: We've also redesigned the weapons, like the pistol. Grif: Sweet! Is it more powerful? Sarge: We prefer the term "balanced". Grif: Balanced doesn't sound anything like powerful. Does it still kill in three shots? Sarge: Of course! As long as those three shots are preceded by four other shots. Simmons: What the hell did we do to these "Bungo" guys?!
In Halo 2, the Plasma Pistol was still the essential part of the "Noob Combo"; a fully charged pistol shot, followed by the BR, would kill an opponent, and the plasma pistol's homing was considered excessive. Bungie remedied this in Halo 3 by lowering the homing and making it so that the pistol would steadily consume ammo while charged, making it impossible to keep it primed for firing at all times.
The plasma pistol got back most of its homing in Halo: Reach, making the n00b combo practical again (though only for about 3 or 4 kills before the pistol runs out of energy). The homing also makes the pistol much more viable for disabling vehicles with its EMP effect (which was added in Halo 3 to offset how nerfed it was otherwise).
Halo 2 also has the infinite energy sword glitch, and the infinite invisibility glitch, which Master Chief can also use (if you get the Envy skull).
The sword glitch doesn't really do that much. On the levels where you really need them they're in generous supply anyway.
Halo 2 had jackal snipers in the campaign, which were one-hit-kill at all ranges on Legendary. It essentially made getting past parts of the level with snipers a lottery, since no matter how well you can aim, you'll have to rely on the computer deciding not to randomly kill you.
Halo 2 had some other issues that became more apparent in large scale objective based gametypes: the first was the rocket launcher's lock-on ability which effectively made all vehicles death traps, the banshee could avoid the rocket by rolling but only if the pilot knew he was being fired at, knew from which direction, was facing the right direction and timed the roll totally perfectly. The sniper rifle was also a complete beast, even if you didn't make the headshot its rate of fire was so high you could easily do double body shots. Teams spent entire matches just fighting for possession of these weapons simply because once a team had them all the outcome of the game was usually a foregone conclusion since the other team could no longer use vehicles nor walk anywhere and invariably got bottled up and slaughtered and the issue was only compounded by the utter worthlessness of the smg spawning weapon at any range greater than ten feet. Notice how the rocket lock on never returned in the later games, and how Bungie went out of their was to make maps hilly and filled with gullies in Halo 3 onward to break up sniper sight lines. Then when that wasn't enough they gave the sniper significant recoil in Reach.
They also made the Reach sniper into an anti-tank rifle. Before, the only way to disable a tank was to snipe out its driver (if the canopy was open). Now? Just shoot it twice anywhere. It's overpowered to the point that getting into a tank is basically asking to to be near-instantly killed.
The rocket lock-on came back in Reach, but very briefly. Very briefly. Near the end of Sword Base, you're supposed to kill a couple of...well, they say Banshees, but it's actually a Phantom and a Banshee. And trying to do that without lock-on would just be ridiculous. A Mercy Moment from Bungie, if you will.
The not-so-well-known Scarab Gun, which looks exactly like a Plasma Rifle (save a few small physical traits) but fires fucking death lasers. Slow death lasers, but death lasers nonetheless. It's so named because it fires the same shot the Scarab uses and, like the site says, the damage the Scarab Gun hits per is insanely high. It's only available for one level though, and ridiculously hard to get to (it is an Easter Egg, after all). But, nonetheless, death lasers.
A level in Halo 3 becomes idiotically easy if you hand the Fuel Rod Gun to a Marine. Remember, these guys have good aim and limitless ammo. "Crazy Rod" would go nuts on the Covenant with that weapon—even causing an event to be averted by taking out a troop ship before it landed.
Halo 3's battle rifle essentially obsoletes most other weaponry save for power weapons.
So far, Halo Reach has roughly balanced everything out, save for one thing - the Scorpion. In previous games, the Scorpion was gradually nerfed so that it could only kill small vehicles in one shot from its cannon. In this game Scorpions can take out anything,even other Scorpions, in one shot. Tank beats everything has never been truer. The bitching got so bad that Bungie removed them from Hemorrhage (a remake of Blood Gulch/Coagulation with a bit of Valhalla thrown in) in matchmaking in favor of the more balanced Wraiths from Coagulation.
The stupid thing was that the wraith was designed to be a low damage, high health tank in comparison to the scorpion. They also tilted scorpion stats the other way... To the point where the scorpion's powerful attack negates the wraith's higher health and kills it in one hit anyway, and vice versa with the wraith. Of course, the wraith's projectile doesn't travel nearly as fast.
Halo 4 also has the game-breaking ability to spawn with a Plasma Pistol and Plasma Grenades. It's safe to say that most people now have an anti-vehicle class read for when anyone uses a vehicle.
The Boltshot should also be noted, charging it will instantly kill anyone within ten feet.
Another Bungie game, Marathon, has it so the rocket launcher is one of the few weapons you can easily get kills with.
The Conduit: In addition to the SPAS-12 + punch instant kill combo, there's also the SMAW rocket launcher. Area of effect instant death, and you can two-hit KO with a melee attack if you miss. Camp near an ammo box and you can do all of the above AND spam normal grenades. The there's the radiation grenades...
In multiplayer mode of Serious Sam 2, if ammo was set to unlimited and someone picked up a serious bomb, then it was possible to use it over and over and over again. Since serious bomb clears the screen from all enemies except bosses, it is a REAL game breaker.
It had its limits, though. You couldn't move from where you picked it up, as it'd disappear from your inventory if you did.
Any technical truck with a Mk. 19 on it in Far Cry 2. It is among the hardest hitting weapons in the game, can start lethal fires, and has unlimited ammo. It also has great range, especially from a high position.
The MGL-40 Scoped Grenade Launcher could count too. It kills everyone including all vehicles except for your buddies at the end of the game
Metroid Prime 3 had one with its Hyper Mode. Going into such a state makes Samus invincible for several seconds. However, being in this state for too long makes her corrupt and unable to exit Hyper Mode manually and letting the meter rise will cause terminal corruption. Shooting your weapons during this dangerous state lowers the meter, so one could just play a game of balance the meter and never be harmed by enemy attacks for 30 seconds (at which point the mode ends). Sure, it costs a whole energy tank in the process, but since energy is easy to find, it can make even hyper difficulty pretty easy.
You could also just use Hypermode purely as a shield. Engage it and quickly run through dangerous territory without attacking anything, making sure to disengage it before the 10 second mark (the point where you enter corruption mode). Since corruption mode didn't occur, your (full) Hypermode energy gets returned to your energy supply, resulting in no energy lost. If 10 seconds isn't enough, just quickly disengage it before the 10 second mark and engage it again to avoid corruption. It's also ideal for certain boss fights when the boss is unleashing a particularly nasty or hard-to-avoid attack.
There are a few balances for Hypermode in the game. It's timed, especially when you get into corrupted hypermode where you need to discharge very fast or lose the game. That's the obvious one. Also, it's not truly invincibility as damage you take can contribute to your corruption (Especially on the last planet of the game.), it's also basically an ammo system even for things you'd normally get unlimited in normal mode. It also costs health to fire your weapons in Hypermode, which you'll find you have to do at many points in the game. The leviathan seed bosses REQUIRE liberal use of Hypermode weaponry to damage them, but also a LOT of pre-seed objectives require liberal usage of the same Hypermode tactics to succeed: On Bryyo you have to enter hypermode to keep respawning flying enemies at bay while you pull switches to allow you to take out anti-aircraft weapons blocking your ship from shooting out shield generators. On Elysia, you have a fullscale escort mission of abomb where you have to take out pirate transports quickly lest the pod you're on gets destroyed. On the Pirate Homeworld you have to protect Marines from Berserker Knights and other heavily armed and armored space pirates. Oh, and those marines you have to protect have weak weaponry and often get KILLED in one hit. One could abuse hypermode to get through stickysituations without taking too much damage, but Hypermode has too many disadvantages. Also, you'll find yourself on the receiving end of hypermode from a lot of enemies, including the three bounty hunters, the seed guardians are effectively in constant hypermode while you fight them, and a lot of mooks, especially in the Pirate Homeworld, are able to engage Hypermode as well.
Metroid Prime (the first one) has the Plasma Beam. Rapid fire, high power, high speed, and fire elemental. Its only weakness is its low range—which doesn't mean much because the game is a shooter to begin with so Instant Death Radius is a minor problem at most. (All beams have infinite ammo in Metroid Prime.) Its fire elemental nature would have been a weakness if not for the fact that it was so powerful it could kill enemies in Magmoor Caverns faster than the Ice Beam anyway. Of course, it is available for only the last quarter of the game (short of Sequence Breaking), so at least only that is broken apart.
The Wavebuster. While it easily eats up your missile reserves, it sends a rope-like beam at the enemy and effectively drains their health in seconds. It's useful in boss fights since it can attach to the boss's weak point, and it can easily bring down Meta Ridley if you have enough missiles. Utilizing so-called "Secret Worlds" (areas outside the standard game world) you can even use the Wavebuster to kill Puzzle Boss Flaahgra. It was toned down significantly for the PAL release and later editions.
Metroid Prime 2: Echoes has the Annihilator Beam and Light Suit. The Annihilator Beam will supercharge light beacons and crystals, causing darklings to literally just walk in and kill themselves. The Light Suit makes you invulnerable to all environmental damage in the Dark World. You only get them at the very end, but when you do, Dark Aether actually becomes less hostile than Aether.
The game Second Sight has the improved version of telekinesis. Just hold your near-invincible Psychic Trooper enemy still for a bit and grab him. Then knock him out. Oh, and this takes very little power.
Star Wars Battlefront 2 gave us the Engineer class who is equipped with a shotgun which is extremely effective at close-to medium range, a fusion cutter, with which they can disable mines, an ''immunity' to said mines, detonation packs which they can explode at any time they please, which can incidentally be detonated the moment one is thrown out and to top it off, they have health and ammo packs which are meant to be given out to other troops, but can be used to restore the player's personal health and ammo. A decent player using this class will be nigh unstoppable.
The Engineer class in the original Battlefront probably counts too, with his medpacs and semi-automatic grenade launcher, which is the second-most powerful weapon in the game. If you can get used to the launcher's erratic firing arc, you will dominate most of the other classes in the game.
In Space battles, both the Droid Tri-fighter and the Rebel A-Wing were unbalanced due to the mechanics of the missiles they fired. The Tri-fighter fired blue seeking missiles which had better turn rates and pursued a target for far longer (and many times in circles) than the other missiles. The A-Wing fires all its missiles in one burst, meaning getting hit is a one hit kill.
And then there was Mos Eisley in assault mode, unique for featuring nothing but hero units (which were almost always turned off for regular gameplay), was poorly balanced. First there was a glitch where the lightsaber animation played twice, doing double damage and stun locking the target. On the heroes side, there was Force Pull, which had ridiculously long range and stunned the target momentarily, leaving them helpless to the the Jedi waiting at the other end, ready to slice them up. And on the villain side, there was Force Choke, which also had incredible range (not as much as Force Pull, but greater than Force Push), and was unblockable. And finally, shooting characters were worthless to begin with.
And then there's the amusing choke/lightning combo the emperor can use, most often seen in the Mos Eisley assault mode. In short using choke on a target sticks them in midair unable to take any actions. So long as you don't release the 'choke' button you can immediately switch to force lighting and start shooting lightning at your target, negating choke's main weakness (taking a long time to kill). In other words you instantly pin any single target in midair then lighting them to death quickly.
Han Solo, useless in almost any other situation, can kill any computer controlled Jedi 100% of the time, by running away backwards, throwing his remote detonation explosives, and triggering it as the Jedi runs over the top of it.
In the first game in Mos Eisley, when playing in the Clone Wars era, the Separatists get an AAT (battle tank) and the Republic gets no vehicles or AT turrets. The crowded design of the map made it near-impossible to take it anywhere other than the hangar it spawned in, but it'd still be hell trying to take over that command post.
Just about every damn upgrade you could get in the game made things incredibly easy even on the hardest settings. That pistol every class bar specials gets? Get enough kills per life with it and it gets upgraded into a mini sniper rifle that can kill in one shot at any range. The soldier's rifle? Becomes incredibly accurate, and fires in short bursts capable of taking down anything but tanks in a few seconds. That shotgun engineers carry? Upgraded to a Flechette Shotgun capable of taking down even Wookiees in one shot at medium range. And the rocket launcher Heavy Troopers and Vanguards carry? Upgraded to a remote control missile launcher that can hit vehicles in their weak points from the other side of the map.
The Cloak mode in Crysis is 100% effective and works against all enemies. Proper usage of it can allow you to waltz through even the Harder Than Hard difficulty setting.
The flying tank VTO Ls in Crysis multiplayer, which can destroy enemy helicopter by ramming them. They also have homing missiles.
Pre-patch gave you the god-like AA Guns in multiplayer. Essentially the AA guns were the de-facto armor you would purchase. They only cost 350 points (ie: 1 or 2 kills and you can purchase it if you didn't purchase anything at the beginning), and were thus one of the first few vehicles thrown out there. What made them game breaking was the fact that the vehicle has dead-aim (100% accuracy for something that is supposed to only throw up 'flak' at air vehicles), and it could literally take down any vehicle in two shots. First bullet puts the vehicle into "bail out I'm gonna crash mode", and the second is to collect the points for the kill. You were also given 250 rounds for it out of the gate. Essentially, matches boiled down to: 1) get AA, 2) throw it on a hill or something that overlooks a vast majority of the map, 3) two-shot anything that comes into your line of sight. A patch drastically nerfed (or maybe fixed?) the AA guns, turning them into the ever-lovable flak-tossing useless against everything vehicle that nobody uses anymore.
The last 2 Jedi Knight games have one nasty tactic, a quick pulse of Force Grip (even at its first level) forces an opponent to disable his lightsaber, allowing you to tap grip, (optional) tap a force speed hot key, then maul over the enemy who is dead by the time they reactivate their saber.
Players in G 4 Tv's Multiplayer competition show Arena found an even quicker version in Jedi Academy: You hold, your buddy goes to town with his Lightsaber. The announcers referred to it as the "Force Pinata", and in the 2-on-2 games played in the show, it meant swift death to any team whose members got separated.
Prepare to never play these two games online again. Virtually every game server not an official Mod server will feature a pack of "leet" players who specialize ONLY in gamebreaking maneuvers, such as "gripkick" and practice for endless hours, such moves as a Force Grip at full level, and spinning themselves with such speed and accuracy, that it is quite literally impossible to break free. They add further humilitation to this by speedy moves involving jumping up, and slamming you to the ground for an instant-kill, regardless of your health level. "Gripkick" consists of Force Gripping, then dragging the person close enough to perform a nonstop series of back-flip kicks to them until they die. There's also a lightsaber move with the Heavy stance by which when swinging sideways, they twist their mouse in the direction of the swing, so the lightsaber stays in one place. This is an instant-kill if it sticks into someone.
Although the inherent idea of Jedi vs. the Trope Namers for Imperial Stormtrooper Marksmanship Academy is broken in a Rule of Funny way, there's a comical trick in singleplayer that can utterly destroy any non-Jedi opponents: Force Jump + Force Pull. You can make a graceful landing from a hundred feet in the air; stormtroopers cannot. Rinse and repeat until the room is empty.
In the first Jedi Knight (Dark Forces II), the Force Protection power you can get pretty much nulls all laser damage and seems to sometimes block lightsaber damage. Plus, it has no cooldown time. The game becomes pretty easy after that.
The system for leveling non-core powers in Jedi Academy can make anything a game breaker in short order; as soon as three levels into the game, you could have fully-leveled Heal (essentially giving you plot armor), Mind trick (anything without a lightsaber switches to your side), Lightning (anyone in front of you fried instantly), or Grip (combine with Bottomless Pits or long falls and everybody dies, lightsaber or not).
In Rainbow Six Vegas 2, the ending of the first mission involves the player character, Bishop, guarding a team member as he attempts to defuse a bomb. By using a simple trick (before your team member gets to the bomb, throw a grenade at the door the bomb is near), and hiding behind cover, you'll be able to see a terrorist manning a turret. As soon as you kill him, another one respawns from the pillar right beside the gun. Instantly. And with no delay. You can kill the terrorists ad infinitum (as long as you have ammo) to level up all the way to Elite Status in an hour. If you run out of bullets, die, then repeat the same procedure. The snafu was fixed, but if you have the original game, you can carry this out at will.
A still-unpatched glitch allows perfectly-accurate blind shots with sniper rifles. Press the aim button, place the blindfire crosshair over the enemy as normal, and take your shot; it'll hit them as if you were actually looking through the scope. Makes harvesting CQC points incredibly easy.
The Black Tarot in Painkiller can become a genuine Game Breaker with the right card loadout, even if some of the cards are earned at the very end of the game and through really difficult conditions. For example, try equipping Dexterity (weapons reload twice as fast), Rage (guns do quadruple damage) and Triple Haste (world moves as 1/8th speed) and go to town...or equip Forgiveness on top of that and do it three times per level.
The classic Call of Duty Game Breaker is the PPSh-41; in the original, it had a huge 71-round magazine along with very friendly and predictable recoil and an excellent iron sight. Almost every later game tried to Nerf it somehow. For that matter, submachine guns in general have always been overpowered in the World War 2 CoD games, and the only truly noticeable nerfing any of them got was the Thompson's slight magazine reduction from 2 onward.
CoD 1 also had the scoped Mosin-Nagant; while every other scoped rifle had to reload rounds one at a time, the Mosin-Nagant used a stripper clip whether scoped or not, giving Soviet snipers a huge advantage in multiplayer.
Apart from the other broken scoped rifle, of course. The FG42 in the original game was ridiculous; a selectable semi / full-auto high-damage weapon with an extremely accurate scope, it was a true do-everything gun with no meaningful weaknesses whatsoever.
Call of Duty 4: Modern Warfare has the grenade launcher: an attachment that can be used with any of the Assault Rifle-class weapons, is perfectly accurate, arcs over obstructions (which also handily lets it ignore the effects of cover,) requires about ten seconds of practice to master, is an instant kill if you're anywhere near the impact, and you spawn with two rounds. There is no downside to using the "Noob Tube," and you essentially get not one but two free kills after every spawn.
Due to an oversight, attaching the ACOG scope to the M40A3 sniper rifle increases its base damage from 70 to 75. While this may not sound like much, the damage multipliers on shots from sniper rifles are coded so that a player with the Stopping Power perk (which multiplies bullet damage by 1.4x) will deal 98 damage on a "bad" hit, like to a target's foot, barely letting them survive a single shot with the default 100 max health. As such, the M40A3 will literally be a 1-shot kill anywhere on the body unless your target has the Juggernaut perk to increase their max health, and even then a shot anywhere that's not a limb will be a kill.
Another oversight had the Skorpion's base damage unaffected by the suppressor attachment. This was especially noticeable in Hardcore mode, where said damage is higher than the maximum health players are given, combined with the gun having practically no recoil for ranges where a single bullet won't do the trick. The weapon was universally banned from competitive-league games for this reason, even after it was patched.
The Rifle Grenades in Call of Duty: World at War. They're pretty much accurate rocket launchers. If one uses them, they will be hated.
The MP40 was laughably overpowered as well. Coupled with dual mags, and using the Stopping Power and Steady Aim perks virtually guarantees you'll slaughter the enemy.
The Model 1887 shotgun in Modern Warfare 2, prior to patching. It almost always instantly kills the target (even without Stopping Power), and can still hit at a long range despite the typical uselessness of shotguns in this series. Here's the real kicker: they can be dual-wielded. Infinity Ward themselves acknowledged the problem and issued a patch to "balance" it, drastically lowering its effective range.. Unfortunately the first patch only applied to its akimbo version, meaning a single 1887 is just as bad (or good, depending on what side of the weapon you're on) as it always was. Furthermore, using the Bling perk for two weapon attachments - Full Metal Jacket and Akimbo - would effectively give you the pre-patched version of the dual 1887s, as well as the increased penetration of FMJ. A second patch reduced this problem.
Additionally, there's the M93 Raffica machine pistol, also known as the "Pocket M16." It can effectively deal one-hit kills, so long as the full burst hits. Also, the game treats it as a pistol, meaning it gets swapped to very rapidly and can be used in Last Stand. Unlike the one-burst-kill assault rifles, it can also be dual-wielded to great effect.
The UMP 45 is approaching this, unless a submachine gun is supposed to be able to kill a target in three bullets while silenced and still allow incredible mobility while running and aiming.
Can't leave out the Noob Tube/One Man Army/Danger Close combination. The Grenade Launcher (or "Noob Tube") is, as in Call of Duty 4, very powerful. However, you only get two grenades from spawning. The One Man Army perk allows the player to switch between classes on the fly, including to the class they are switching from. This allows an infinite stream of grenades to toss with only a short delay in switching between classes. Danger Close deals more explosive damage with a larger area of effect.
It should be noted that since the Grenade Launcher has reliable pinpoint accuracy, players can learn spots to stand in and where to aim in the sky so that they can infinitely spam explosives from across the map on contested points, like flag/bomb sites.
And the Scavenger perks allows you to refill your ammo from dead opponents, including grenades. Opponents you likely just killed with your grenade launcher.
Also notable is the G18 attached with Akimbo with the Steady Aim perk, allowing greater firing from the hip. Combined with Stopping Power, Scavenger, and the aforementioned Steady Aim the player is given a nearly unending bullet hose.
The combination of three perks: Marathon (lets you sprint infinitely), Commando (allows you to instantly lunge forward a ridiculous distance when using the knife), and Lightweight (increases movement speed). Combine with the Tactical Knife attachment (which increases the speed at which you can pull out your knife), and there will always be someone running at inhuman speed and stabbing people from across the room for one-hit kills every time. The worst part is these three perks are unlocked by default.
As overpowered as it, it isn't as broken as it used to be. Holding a Care Package marker (or a Sentry Gun/Emergency Airdrop marker, but everyone used Care Package because it's only four kills) would grant a speed increase that would stack with Lightweight. Effectively, you'd run at roughly 200% speed with the ability to slide ten to fifteen feet towards someone and instant kill with a knife; lunging also grants invincibility frames if your opponent doesn't shoot fast enough. To top it off, as you're running so damn fast, on everyone else's screen you'll be crouching while running so you're even harder to kill.
Add the above-mentioned UMP .45 to the 'knife class', and you get a class that can not only sprint indefinitely at higher than normal speeds and lunge across rooms for instant knife kills, but that is also a credible threat at range.
The chopper gunner can also be seen as quite overpowered as it lets you easily spawn trap opponents, leaving them easy prey in most maps (some maps with high cover, such as Skidrow and Karachi prevent this).
AC-130 can do this, too, but typically doesn't have equal killing potential because it has to reload. The trade-off is that the AC-130 is significantly harder to shoot down than a Chopper Gunner.
Prior to patching, the Javelin missile launcher had this reputation. Before the patch, the Javelin could be used to get revenge kills using a glitch causing the Javelin to launch into the ground immediately upon death, killing anyone within 20 yards.
Some of the more controversial gamebreakers are found in Call of Duty: Black Ops. The Famas and its expy, the AUG, are both hated and loved for their insane rate of fire (second only to the G11 within its bursts), powerful damage (second only to the Stoner63 as far as full-auto DPS is concerned), and high accuracy. The AK-74u with the Rapid Fire attachment also gets a lot of approval and disapproval. Although it gets some extra recoil (countered by the also common Grip attachment), its rate of fire is increased to a rate that competes with the Famas and AUG, essentially making it a lighter yet slightly weaker version of them. What makes the Famas, AUG, and AK-74u so controversial is the fact that they're unlocked early (14, 17, and 26), so higher level players generally don't have the upper hand just because they're at a higher level, which was considered to be one of the problems with the aforementioned Akimbo Model 1887s.
A fun experiment is to go into a game lobby and to examine the statistics of all of the players there, and to count the number of people who the two guns they've been killed the most with are the Famas and AK-74u. Hint: It'll probably be much easier to count the people who haven't been killed most by those two guns. The AUG and the Galil usually compete for the third spot.
Descent II's Gauss Cannon, an overpowered upgrade to the Vulcan Cannon that does tons more damage, has the same high firing rate, uses Vulcan ammo as well instead of energy, and most of all, is also Hit Scan in a game where most weapons have painfully slow projectiles. No wonder it was Nerfed into the Vauss Cannon in Descent 3. The first game's Fusion Cannon and Mega Missiles were quite overpowered, and thus were nerfed in the second.
One of the easiest ways to take down any Big Daddy is the so-called DoomCan method: find any sufficiently large object (usually a trash can, hence the name), stick lots and lots of proximity mines on it, pick it up with the Telekinesis plasmid, and toss it at a Big Daddy. Congratulations, you just turned the Boss in Mook Clothing into a corpse.
An even funnier way to kill the "Bouncer" type Big Daddy that use their drill arms to charge at you is to use the crossbow with trap bolts to place four or five electrified tripwires between him and you, then shoot him once and stand perfectly still. The Big Daddy will charge straight at you and get his shit completely ruined by the tripwires, sliding facefirst to a dead stop at your feet.
The Electric Gel for the Chemical Thrower is incredibly rare, and the vast majority of the time can only be obtained by crafting it in specialized vending machines using the junk lying around Rapture. However, not only does it do obscene amounts of damage to Big Daddies, but renders them completely immobile for as long as they're being hit. Combined with the upgrade that cuts the Chemical Thrower's ammunition consumption rate in half, it is entirely viable to stand in front of a Big Daddy, hold down the fire button and just watch it die (or if you want to conserve ammunition for later fights, simply reduce it to a more manageable level and finish it with other weapons).
Proximity bombs are great for a variety of things, like diffusing the game's more infamous "Splicer behind you" traps. Just plant a mine a few steps out from the trigger, and then approach. Event triggers, Splicer spawns on the mine, BOOM. Most boss battles wait for a specific action from you to start, so you can spare a moment before initiating the battle to drop a cluster of Proximity Mines right where the boss is going to enter (or run from) the fight.
There's a unique quirk of the Lot 192 MacGuffin that you come across in Olympus Heights/Apollo Square - when you take the first dose of Lot 192, your plasmid structure will start randomly changing. You won't be able to control what plasmid you have equipped and you can't use Gatherer's Gardens or Gene Banks, but every time your current plasmid randomly shifts, your entire EVE bar will be refilled. Every single time, until you receive the 2nd dose of Lot 192. Not to mention that you can randomly gain access to plasmids you don't ordinarily possess, like Hypnotize Big Daddy 2 if you're on an Evil playthrough.
Judicious use of the research camera dramatically increases damage to the researched target, as well as providing valuable tonics very early on (such as the below mentioned Natural Camouflage). The best part is that these damage bonuses stack with all the other damage bonuses you can pick up.
The Natural Camouflage tonic completely breaks many ambush sequences, where if you stand still long enough to trigger Camouflage before touching the object that triggers the ambush, the Splicers will menacingly jump out and...stand around confused, because their target has apparently disappeared. If you Camouflage yourself standing under a hacked security camera right before a scripted combat sequence starts (such as when Cohen flips out after putting the third picture into his display), you can literally put the controller down and let the friendly security drones clear out all of your enemies.
Any time there is more than one enemy present, the Enrage plasmid is your #1 weapon of choice. Not only does it cost less EVE than the Electro Bolt or the Incinerate, it saves you the ammo you'd spend on the incapacitated enemies yourself (or the time of having to switch weapons, for that matter), and gives you the added benefit of guaranteed Action Shot/Multiple Subject research photo bonuses, essentially doubling your power-up rate. Combine it with a Hypnotized Big Daddy and you're basically a walking wall of indestructibility.note As long as you don't Enrage the Big Daddy, since it undoes the Hypnosis.
Getting all the relevant Wrench tonics (Wrench Jockey, SportsBoost, Wrench Lurker etc.) gives the former Emergency Weapon one of the highest DPS in the game, and coupled with the aforementioned research camera bonuses means that everything in the game that isn't a Big Daddy or the Final Boss dies in a handful of hits. By this point the Electrobolt + Wrench combo (which does 4X damage) is a waste of time.
The Insect Swarm plasmid has all the strengths of other projectile-based Plasmids and none of their weaknesses. It disorientates enemies longer than Electro Bolt and Incinerate!, and also does continuous damage over time like Incinerate! but can also be used with Winter Blast. When upgraded, the insect swarms can attack multiple enemies at once, and when fully upgraded enemies killed by bees become large bee-proximity mines that when approached by enemies will cause bees to come out of the body and attack them, kill them, then infest their corpse and repeat the process over. On top of all that individual swarms last over a minute, there also doesn't appear to be any limit on the amount you can spawn, and the icing on the cake is that bees are not bound by physics and can easily fly through walls. This leads to ENTIRE ADJACENT ROOMS being completely cleared of enemies before you even walk though the door. And the bees actually have very tiny hit boxes, meaning they will always stop large fireball style attacks making Houdini splicers and Big Sisters a complete joke as long as they aren't close enough for them to punch you.
The Fountain of Youth tonic has your Eve restore when you're standing in running water. In Rapture. It's hard to find somewhere this can't be hideously abused, as the Eve system has a quirk where having any amount of Eve in your bar allows you one shot with a Plasmid. Since your Eve refills with Fountain during the firing animation of the Plasmid, you're free to fire off anything but the level 3 element stream attacks as often as their attack animation allows, without ever having to use an EVE hypo. Combine this with Decoy 2 and watch enemies kill themselves without you ever lifting a finger; with Decoy 3, any enemy that does attack you has to do more damage than the enemies attacking the Decoys, since they heal you for every hit. Fighting anything yourself becomes more or less optional since spamming Decoys or Insect Swarms costs you absolutely nothing and is ludicrously effective.
Security Command 3 (summon up to two powerful security bots) coupled with Hypnotize 3 (turn anything that isn't a Big Sister to fight on your side for up to five minutes, Big Daddies included) makes it more dangerous for you to fight yourself, as you risk getting caught in the crossfire. Every time you lose a bot you can just summon another in two seconds, and every time your ally dies you can Hypnotize another. While this has a massive EVE cost there are lots of tonics to mitigate that, including the aforementioned Fountain of Youth.
Left 4 Dead has corner camping/closet camping, which has the survivors all huddled up against a wall corner or in a tiny closet. This forces the infected to rush at the survivors from one or two directions, allowing the survivors to easily dispatch them. This made it very frustrating for the zombie players in VS since Hunters and Smokers that would rush in to attack could easily be shoved and Boomers were useless since being vomited on was just a time waster due to the camping. Valve addressed this issue in the sequel by allowing zombies to come in from more directions so that camping is not desirable and introducing new special infected to further discourage camping such as the Spitter and Charger. Most panic events now force players to keep moving instead of staying in one spot.
There was also a patch to address the problem of melee spamming in the first game. Players as survivors could keep shoving zombies away from them, which made it very hard for Smokers and Hunters to land a hit. Valve then put it a melee fatigue system where shoving too much too quickly will force a cool down, preventing you from shoving until the cool down has passed. This mechanic was applied in the sequel to all modes.
The remedy had worked a bit too well and created another problem, which is rushing. Since most of the crescendo events force players to run ahead to stop the event and the new special infected discouraging camping, survivor players in VS would just rush the level and rarely stop, making it extremely difficult for infected players to spawn in time and set up; by the time you get into position, the survivors are already a mile ahead of you. What makes it worse is if a survivor has a Bile Bomb, they can toss it to distract the common infected and run.
Another issue with melee was a bug in which, by alternating hitting melee and switching to a different weapon/item, you could punch people at Fist of the North Star-like rates, taking out an entire swarm of common Infected just by punching them and taking almost no damage in return.
The Tank is supposed to be a terrifying infected that has the potential to wipe the entire team. This was the case in the first game, but in the sequel, people discovered using melee weapons against the Tank killed it a lot faster than shooting it or setting it on fire. Every melee weapon hit (except the chainsaw) inflicted 10% damage to the Tank, which lead to the Tank being killed in literally 10 hits. If all four survivors start whacking the Tank with melee weapons, then the fight became anti climatic. This became a huge problem in VS mode where Tank players had to deal with survivor players that would smack them, then quickly back away before they could be punched. The damage to Tanks with melee weapons got nerfed in an update where now melee weapons only do 5% damage, or dies in 20 hits, making run and gun tactics more favorable. Of course, people will still try to smash Tanks with Frying Pans and such if given the chance.
In the original game, in "The Crane", the 2nd stage of "Dead Air", there is a Game Breaker right at the beginning of the level. Outside the safe room is a steel door that cannot be broken through by infected and cannot be opened by anyone except the Survivors. This allows the Survivors to stay protected from ALL infected, including Tanks and Witches. Another use is trapping Tanks inside of the room; If a Survivor manages to lead a Tank inside the room, get out, then shut the door, the Tank will be unable to get out. This exploit is only available in Campaign, and does not work in Versus mode.
Don't forget on a few levels, especially in the first game, Smokers were arguably one of the best infected to play. It could force survivors to backtrack, drag them off of ledges, especially for incaps and insta-kills, etc. One tactic would have you make a single swipe at a wooden door to create a small hole. Then shoot your tongue through the hole and grab a survivor. The door creates a makeshift barrier, and the survivor usually blocks the hole, causing massive friendly-fire and general time waster. You could hide behind walls of fire, then shoot your tongue and drag survivors through the fire for massive damage and high chance of flaming hunter pwnage. It also dragged campers out of their corners and even created an annoying fog cloud when you died. And if you had a survivor snagged in your tongue, and they get boomer'd, they can easily die if not tended to immediately. The smoker was not one to be messed with in the right hands.
It was originally possible to attack a Witch as an Infected and lead her to the survivors. Given that there is no Infected friendly fire at the time, this meant the witch could not wound the attacker, and would automatically switch to an survivor once one is in sight. This was later patched to hell as the witch will not attack at all, instead just be wounded till she died.
The 2nd map of The Parish has one for the Tank, similar to the Dead Air example. The CEDA decontamination trailer has two doors that cannot be destroyed, but the glass window in the ceiling can be destroyed only by a Tank. In theory, survivors that try to camp in the trailer could get killed by the Tank since it can drop from the ceiling and the survivors had trapped themselves. However, if the survivors are quick enough or are smart enough to lure a Tank player into the trailer, the survivors can close the door on the Tank and trap it inside the trailer with no way for the Tank to escape.
For awhile, the Spitter was one of the most dangerous special infected, being able to wipe a whole team by herself if the right conditions were met. One map in Dead Center and Hard Rain have an elevator the survivors had to use. If a Spitter player was quick enough, they could spit acid into the elevator as the doors closed, trapping the survivors in a big pool of acid with no means of escape. This tactic was nerfed, making any acid patch shot into an elevator fizzle out quickly.
Explosive Ammo in Left 4 Dead 2 was pretty powerful. While survivors could only get one mag of the ammo for their weapons, explosive ammo pretty much made you a walking powerhouse since it would stumble any special infected that got shot with it, including the Charger and the Witch, but not the Tank. For VS, this made killing Witches easy and stopped any attack by the special infected instantly, which caused players to hoard explosive ammo until the need for it came up. A patched removed explosive ammo from VS entirely.
Some maps have objects that can be punched around by a Tank, including cars. Punched cars are programmed to vanish after some time so survivors can't be blocked from advancing. However, other objects like light posts and dumpsters don't have the same programming, so a Tank player in VS could punch those objects in the path that the survivors needed to go, effectively blocking them indefinitely. Patches were later put in place to make the objects static so they can't be moved.
The AK-47 plus Laser Sight. In normal gameplay, the AK-47 is the strongest of the three assault rifles, balanced by a slower firing rate and horrid accuracy. Find a Laser Sight and you're just left with the lower fire rate - accurate enough to snipe Special Infected before they have a chance to do anything, with power on-par with the scoped weapons alongside a higher capacity, faster reload, and full-auto fire rate. The second map of Dead Center can be very painful to play in Versus for the Infected team, since getting both an AK and laser sights is guaranteed at the gun shop.
Shogo: Mobile Armor Division has the Red Riot, while normally only available at the end of the game on one route, it is also peppered throughout multiplayer MCA maps (Though, usually difficult to get to without the tractor beam function enabled). The weapon, which actually has a track named after it in the game, has a massive range and blast radius, and is strong enough to instantly vaporize even a predator (the toughest and most heavily armored of the four Humongous Mecha available to the players) if it even so much as touches the edge of the blast. While each pick-up only gives one shot, they are hard enough to reach that if you're feeling brave and don't mind the other players getting right pissed at you, you can simply sit ontop of the drop point and get a full stock of 10. Heck, the aforementioned tractor beam in a way is a bit of a game breaker as it lets you cling to the sky box, well out of sight or reach of enemy weapons, while you could simply pepper the ground below with red riot blasts.
The Silver Talon and Heavy Machine Gun in the original Soldier of Fortune. The latter has a built-in white phosphorus grenade launcher that inexplicably uses the same ammo as the main trigger, and it's pretty much the only weapon you'll need for most of the rest of the game. The second game's M4 assault rifle also has a secondary grenade launcher.
Similar to the Modern Warfare example above, GoldenEye Wii has an assault rifle weapon that also has a grenade launcher as a secondary trigger. It was one of the weapons you can start with in the a preset layout by the game online, meaning every time you died, you'd start out with the weapon layout you chose, thus, spamming grenades to your heart's content. If another player online happened to be using the same gun and he was killed, you could pick it up and refill your grenades! It was far too easy to launch a grenade at someone for an instant kill the minute they were in your sights.
Masterton auto shotgun is even more lethal, since you can actually miss w/ the "noobtube/propipe" In the Black Box mode, if someone on the MI-6 team has it, game over!
The MI-6 Team in Black Box in general is this (since they can wreak havok w/ the grenade launcher Basic Loadout), as well as in Heroes to a lesser extent since Bond gets 3 motion-sensing "Proxy" Mines
In most arenas, the MI-6 team has clothing that blends in better with their surroundings, this is most egregious in the dimly lit Industrial, where the MI-6 team is in dark blue/black & the Russians are in bright tan/white. This is reversed in Jungle where the Janus team is in all black, while 2 of the MI-6 guys are bald caucasians... instant headshot!
Singularity has the Statis field, a large bubble in which time is effectively stopped. You can launch it, then stand in it and take your time sending the appropriate amount of hot lead to anything visible. When it collapses, everything you've shot will instantly hit the intended targets. It's also fairly energy-cheap, so easily abused.
In the CO-OP on Syndicate after a couple of games you can have a sniper rifle that is deadly in every part of the body except the chest, fires with full damage through every surface, has an 8 round magazine, and if your not a fan of the zoom, can get an red dot attachment. The full effect comes from when you go into the overlay, showing the position of every enemy on your hud, and killing each said enemy keeps the overlay up longer.
Tom Clancy's Splinter Cell: Chaos Theory introduced an Uzi and Shotgun to the Mercenary team in the Multiplayer Versus mode. These were quickly labelled as gamebreakers because the Uzi's rate of fire was through the roof and, more often than not, caused stupid amounts of lag on the server when fired (as if its potential to kill enemy Spies in less than 2 seconds wasn't bad enough). The Shotgun could kill Spies in a single shot at point-blank to short range.
You should probably just consider that whole mod game-broken on principle. You collect health powerups and HP upgrades faster than enemies can possibly damage you, barring one of them randomly getting a reflect damage shield. To say nothing of the dozens of damage upgrades you find...
In Darkest of Days, extended mags and the fast reload upgrade work this way, especially for pistols. You can behave like you are wielding full-auto weapons, while everyone else seems to have muskets or bolt-action rifles.
The BFG in multiplayer, due to the aforementioned ability to fire off a shot in one room, run over to another player, and then hitscan frag them without them even knowing. They could even kill you first, and still get nailed by the hitscan!
In single player, it isn't any less powerful. Its attack covers an extremely large area & deals massive amounts of damage per hit.
The Soul Cube is pretty damn broken, too. It homes in on the enemy with the most HP and heals you as it slices, dices and makes julienne demon slaw.
In a more retro tone, when a source port is used, the now-ubiquitous keyboard + mouse combo turns the original games' Nightmare! difficulty playable even by a relatively unskilled player, while Ultra-Violence becomes a walk in the park. The monsters were never coded to deal with a player as agile as they are with this combination, even when auto-aim is disabled, and are little more threatening than glorified zombies that can fire projectiles, especially when it comes to open areas. The Cyberdemon is a particularly egregious victim due to the ease of circlestrafing. Most custom maps take note of this, and scale the difficulty accordingly.
The Leviathan super-tank in Unreal Tournament 2004. It has ridiculously high health, moves fast enough to avert Mighty Glacier, fires a continuous stream of homing missiles, and can carry 4 passengers, each of which can spew rapid-fire plasma bolts at anything nearby. It can also transform into a stationary land-based Kill Sat to nuke the pants off of whole battalions of opponents. It's in only one official map, and the whole point of the level is to try to get the Leviathan first so you can steamroll your opponents with it.
Far Cry 3: Blood Dragon has the aerial takedown. Why is it a game breaker? It can be performed just by jumping. That's right, you can perform a Goomba Stomp on enemies. It grants very high cp every time you kill an enemy with it, and you automatically loot the killed opponent once your level is high enough. The only enemies that are immune are heavily armored opponents and non-humans. Everything else dies in one attack. Until you get the Killstar, this is THE best way to take out 75% of the enemies in the game.
Quake has many weapons that could be considered a Game Breaker, but the Thunder Bolt stands out somewhat. Its quick firing rate & high damage made even Shamblers fall to it in a matter of seconds. Unfortanetly, it has limited range, ammo for it is scarce & using it underwater will discharge all of its ammunition & kill you, along with every enemy who also happened to be in that body of water. Collecting a Pentagram of Protection, however, makes you immune to the damage while killing everybody else in the pool of water, even though it still discharges all of your ammo and hilariously reports that you killed yourself despite the fact you survived.
The laser cannon in Scourge of Armagon does away with most of the Lightning Gun's cons in exchange for a slower firing speed.
The BFG10K from Quake II, which is a cousin to the original BFG from Doom.
The Railgun is Quake 2's version of a sniper rifle. Its base damage is 150, enough to kill most enemies in one shot.
The Nailgun in Quake 3/Q3 Team Arena. It fires 9-inch spikes in a shotgun-like formation. Anyone that's not holding a Guard powerup is going to die in one shot if a decent amount of the nails land. Even if it does survive, it gets pushed back with an even stronger push than the Railgun, and in Space Levels, it is almost a guaranteed Insta-Kill. If they don't die from the nails, they'll get pushed into the Void and die anyways.
''Vietcong has the M60. More Dakka? Check. Having lots of ammo? Check. Balanced recoil? Check! It's so broken that it pretty much turns any of its user into John Rambo.