Any FPS that forgets to assign a maximum fire rate to one or more semi-automatic weapons. Used with fast fingers if you want to put in the effort, or with an auto-clicking macro software (or assigning "Fire" to spinning the mouse wheel) if you don't, such weapons can turn out to be more powerful than the game's ultimate end-level guns.
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.
Another particularly egregious example of this trope can be found in a Minecraft mod, of all things. Flans Mod adds guns to the game, including semi-automatic rifles such as the G3 and M14. In the code, said rifles have a rate of fire of 1 - i.e. 1 shot every in-game tick (usually 1/20 of a second) - but are obviously limited by how fast you can click. However, tacking a Full-Auto Fire Upgrade to the gun removes this restriction, allowing you to fire rifle bullets at a staggering 1,200 rounds per minute... if you can handle the recoil. Have fun!
Halo: Combat Evolved's plasma pistol did this. 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. This was altered in subsequent Halo games. However, the "rapid-twitch" came back (sort of) in Halo: Reach, and could be shot even faster. It was practically a fully-automatic weapon.
Otherwise entirely forgettable game Gore had the pistol working like this as well, which could make it preferable to the machine gun.
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 semi-auto 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.
They put in an item that allows you to temporarily see your opponents through walls. During a time when rampant hacking was on the rise and the player base was getting increasingly irate. They put it in the cash shop, when most game hacks would allow you to do the same for free and with no time limit.
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 equippable 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 usable 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. They are just as heavily banned as the AWP, and simply getting a kill with one when they're not banned will immediately prompt the entirety of both teams to use them exclusively.
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. In response to this unscoped shots were made to no longer hit exactly where the crosshairs would be, instead randomly landing a few degrees off-center.
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.
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 game attempts to balance this by having your enemies equip it as well - and, in contrast to some other games that have penetrating weaponry, the bad guys will one-shot you through walls with it, causing many a frustrating death.
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 always at least somewhat larger than the explosion effect itself. Explosions in this game can last quite a long time, and any destructable object in the environment explodes, (barrels, crates, file cabinets...) and any explosion will cause any other exploding object to blow up 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, Spiritual SuccessorPerfect 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 immediately after respawning 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. Oh, and the final boss). 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.
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.
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.
There's even more in Battlefield:
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 an extremely 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 engine. 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, the passengers inside the Blackhawk had access to their tools, so they could repair the Blackhawk while still inside it; third, combined with the above, the Blackhawk had space for three passengers; 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 eventually, however, nerfed into uselessness and obscurity. For the curious, the reason it was impossible to do this for the MEC or Chinese helos was that they were much slower, less armoured, bigger targets, and their guns were crappy machine guns that could barely hurt an infantryman.
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 from legitimate sniping.
The Medic class in general. It can heal itself, revive dead allies, and can unlock the G36E, one of the highest-damaging, most-accurate guns in the game. 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, ironically the one that fixed the USAS-12, 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 (or a shortcut pack) 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 Play4Free had the scout helicopter in Dragon Valley. In theory, its purpose was to harass infantry and quickly deliver small fireteams. Instead, the team who captured B first ended up with a second attack helicopter. Scout helis are the fastest and most maneuverable aircraft in the game, and pack twin miniguns. This allowed them to fly over to a firezone and utterly destroy any infantry that were caught in its crosshairs, all while moving so fast that it was damn near impossible to tag it, let alone shoot it down. After the infantry are 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 that 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!
Halo: Combat Evolved's pistol allows for instant-kill headshots against unshielded enemies, and can break player shields in two hits anywhere. 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. All this leads 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. The only things which could reliable take it on with a chance of winning were Scorpion tanks, other Banshees, and turtling players. 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 a burst from the Battle Rifle, 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. However, 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).
The infinite energy sword glitch, and the infinite invisibility glitch for the Arbiter, which Master Chief can also use (if you get the Envy skull). That said, the sword glitch doesn't really do that much; on the levels where you really need them they're in generous supply anyway.
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 changed in later games to only work on highly evasive flying vehicles.
Bungie tried to rectify some of these issues in subsequent games; in Halo 3, the lock-on function was given to the nearly useless support weapon, the Missile Pod, which was almost useless against Banshees (the only aerial vehicle on all but one map). They went out of their way 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 Halo: Reach.
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.
Levels in Halo 3 can become 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.
The battle rifle essentially obsoletes most other weaponry save for power weapons, thanks to almost all the guns in the game being fairly short range, and BRs being frequently massively abundant if not just starting equipment. While the gun wasn't hitscan, and had a spread with the damage being coded to only count the damage counted from the bullets in the burst which hit the target (rather than counting the whole burst as hitting if a single bullet made impact), its 4-shot kill capability made up for it.
The Spartan Laser could instant kill anything with one shot from any distance on account of being almost hitscan.
Halo: Reach 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, while the Wraith's damage is so low by comparison that the Scorpion, even with its low health, can still just tank the hit and kill the Wraith before it can get another shot. Of course, the Wraith's projectile doesn't travel nearly as fast, so even that first hit isn't certain.
The grenade launcher can be this to those who really know how to use it, doubly so in firefight mode. It can do decent damage over a wide radius, and with skill you can control exactly where you want it to detonate and EMP vehicles. In firefight you are given resupply crates, alleviating the weapon's normally high consumption rate, and it becomes perfect for blasting through waves of grunts and taking down elites.
The sniper was turned 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 and going on the attack is basically asking to be near-instantly killed if you did not coordinate with a team who could be trusted to keep control over the power weapons and watch your back.
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, as 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. Then 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.
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 sticky situations 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: high power (so powerful that a charged shot will vaporize all but maybe one or two non-boss enemies in the entire game that aren't immune to the Plasma Beam), 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 and might only be an issue in the final boss battle. 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 eighth 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 has high power, automatically homes in on enemies without locking onto them, high fire rate, and 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 and allows easy and fast transport between Energy Controllers. You only get them at the very end, but when you do, Dark Aether actually becomes less hostile than Aether (as Aether has no health-regenerating pockets like Dark Aether), save for the more common Phazon spots, as the Light Suit doesn't protect against it at all.
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.
The Engineer class in 2 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. That fusion cutter can also be used to repair destroyed ammo and medical droids, fix damaged vehicles, and even bring your flagships' shields back online in space battles if you're patient and/or get enough of them working together. It can also hack enemy vehicles, booting out the occupants and letting you take their tank for your side (and unlike destroying them outright, stolen tanks don't respawn). 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. The balancing act here is that both are glass cannons to the point that a single hit from the enemy capital ship's defenses will instantly kill them, though that just means they're great for defending their own capital ships.
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), which 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 above 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 VTOLs in Crysis multiplayer, which can destroy enemy helicopters 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 game-breaking 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 humiliation 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 opposite 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.
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 also 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.
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 face-first 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 defusing 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 default drill is a melee weapon which deals only moderate damage and burns through fuel like a mofo, making it less than ideal for dealing with the large numbers of fairly tough, and often gun-toting, splicers. The fully upgraded drill has greatly increased damage, consumes fuel at only a trickle, projects a shield when spun which can send bullets back at shooters, and can perform a lunge almost quick enough to count as a Flash Step with a ridiculously long range and damage high enough to kill the great majority of enemies in a single hit. It can break up crowds. The drilling standard attack stunlocks enemies.The bash attack costs absolutely no resources to use. And then there is a tonic which restricts you to only being able to use the drill and plasmids, but makes the drill even more powerful.
The Fountain of Youth tonic has your Eve restore when you're standing in running water. For those unfamiliar with the BioShock series, this game takes place in a ruined underwater city. 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 2 (summon up to two security bots) coupled with Hypnotize 2 (turn a splicer to fight on your side) often 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. Upgrade to level 3 and the bots are nigh-indestructible, especially with dedicated tonics, and you can Hypnotize anything that isn't a Big Sister. While this has a massive EVE cost there are lots of tonics to mitigate that, including the aforementioned Fountain of Youth.
Lots of Gear items are deliciously exploitable, like Head Master (+50% critical damage, which includes headshots, enemies stunned by certain Vigors, and the Handyman's heart), Rising Bloodlust (damage is increased after each successful kill, up to 5, for ten seconds), Sheltered Life (ten seconds invulnerability after using a health item), and Winter Shield (brief invulnerability after going on or off a Skyline, which are in most major battles), but the best results come from focusing all of them into one specific combo. For example, using a fully upgraded Charge Vigor with Burning Halo (70% chance that a melee target is set on fire), Brittle-Skinned (melee target takes 2x damage for 5 seconds), Executioner (25% extra melee damage) and Overkill (killing with excessive damage stuns nearby enemies) turns Booker into a zooming melee juggernaut that can wipe out whole groups of regular enemies in seconds. Use Blood to Salt (40% chance of receiving Salts after a kill) instead and Booker can zoom around Falcon Punching people almost endlessly.
In Burial at Sea Episode Two the Peeping Tom plasmid enables Elizabeth to see nearby enemies and pick ups through walls, when held she turns invisible and enemies can't attack her even if they're literally on top of her, and there are two upgrades that make both these uses cost no EVE as long as she's standing still. Once fully upgraded using weapons becomes completely unnecessary.
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 in 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 being a 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 a Boomer puked on them too, 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 NPC-on-player friendly fire, this meant the Witch could not wound the attacker, and would automatically switch focus to a survivor once one is in sight. This was later patched; now the Witch will not attack other Infected at all, even if they damage her enough to kill her.
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 is pretty powerful. While survivors can only get one mag of the ammo for their weapons, explosive ammo makes you a walking powerhouse since it stumbles any special infected that gets shot with it, including the Charger and the Witch (though not the Tank). This makes killing Witches easy and stops any attack by the special infected instantly, which caused players to hoard explosive ammo until the need for it comes up. Due to the obvious frustration this can cause to an Infected team, a later patch removed explosive ammo from Versus 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 with the grenade launcher. 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 with the grenade launcher Basic Loadout), as well as in Heroes to a lesser extent since Bond gets 3 motion-sensing proximity 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.
At the end of the game, you get the super TMD, which magnifies all abilties and has no energy constraints. Enjoy endlessly blasting everything to smithereens with pulse!
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 you're not a fan of the zoom, can get a 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.
Naferia's Reign: Invasion of the Dark Mistress has a lot of potential examples of this, being a Game Mod that's possibly still in progress. One example being that with the right equippable items on a specific character, money can easily be dropped by busting ATMs while said character is at point, and said character can then fix the ATMs for a few thousand dollars, allowing more chances for money to drop, potentially in amounts greater than the price to fix the ATM to begin with. You can do this over and over without a limit to how many times said character can fix the ATM.
One other example is a claims from players that the gliding ability of another specfic character can effectively prevent them from ever suffering falling damage, but this only works if you activate the glide a fair bit above the ground, as you will not instantly decelerate upon activating it, and said character is still more than capable of taking fall damage if you're not paying attention.
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 has muskets or bolt-action rifles.
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.
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-140 Scoped Grenade Launcher could count too. It kills everyone including all vehicles except for your buddies at the end of the game in a single grenade.
Far Cry 3: The Bizon, MP5, AMR, GL-94. The MP5 has great accuracy, good power, and can be surpressed and given an optic, allowing you silent damage output normally associated with an assault rifle with the speed and maneuverability of an SMG. The Bizon is a straight upgrade for the second half of the game, with a better rate of fire and an enormous 64 round magazine. The AMR is a "Signature" sniper rifle which, at the cost of not having the option of a suppressor like the regular version, can kill anything in just a single hit - up to and including vehicles if you shoot for the engine - and is made available simply for collecting 20 artifacts across the game (though the cost to buy it in the first place is positively heinous). The GL-94 is a pump action grenade launcher which can start fires. It also instant kills vehicles and heavies, and is automatically given to you as part of an early mission. Thanks to the way weapons are acquired in this game, it's possible to be equipped with free game breaker guns before too long. This is sorta balanced by gear limitations in money and ammunition you can carry, as well as the relatively miserly profit margins from enemies on the first island, and they also seldom carry anything other than assault rifle or shotgun ammo. And sightlines in the jungles of the first island make sniping seldom viable. But once you get to the second island with its open but hilly terrain, have fun.
More than anything else in the game, acquiring upgrades to your stealth, reducing your fall damage, allow you to takedown nearly any dismounted enemy, increasing the quality of your non-healthkit heals, and allowing you to automatically loot any enemy you takedown, makes you broken by design. Out of these, the instant loot, improved stealth, and catholic takedowns make you the most broken. Thanks to these, patrols and guards can be instantly eliminated unawares, and you can immediately get in position for the next ambush without having to stay out in the open to loot bodies.
Far Cry 3: Blood Dragon has the aerial takedown. Whereas Death from Above in the original game was situational at best, here all you need to do is simply jump over an enemy. 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 I 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 Rocket Launcher, not because it's excessively powerful, but because of what Quake is widely known for: Rocket Jumping. When used well, it completely breaks the flow intended by the developers, allowing the player to sequence break or access secrets easily, to the point where an Any% speedrun of the whole game can take less than fifteen minutes.
The Railgun is Quake II's version of a sniper rifle. Its base damage is 150, enough to kill most enemies in one shot. It's also deliciously imbalanced in multiplayer, as 150 damage is enough to kill any player who hasn't found a megahealth or a suit of armor. In any map that has a railgun and a player proficient in its use, boosting one's health is an absolute necessity after you spawn - just getting in random fights as you'd do otherwise is guaranteed to get you pureed as soon as the railgunner spots you.
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.
Shotguns were this in the first few months following the game's release. Thanks to how the game code handles the spread and damage of shotgun pellets, you could do full damage at ridiculous ranges as long as even one of them hit the enemy. This was later nerfed by limiting their range, but some shotguns, particularly secondary ones like the Locomotive and especially the Judge, are still favorites.
The Grinder perk deck before the perk deck balance update completely broke the game on any difficulty that wasn't Deathwish. Thanks to the fast health regeneration, you could become almost completely invulnerable as long as you kept doing damage and had ammo to spare. With a crit dodge build it becomes even more overpowered.
The Buzzer melee weapon will amost always stun any enemy (even Cloakers - hell, even Bulldozers, though only for half as long) for about four seconds with a single hit. In addition to this, it has a full 30 concealment, making it a good choice even with crit dodge builds.
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 user into John Rambo.
Team Fortress Classic, a GoldSrc remake of the old Quake Team Fotress mod, has the Shotgun and Super Shotgun. Why? A programming bug resulting in the absense of fall-off damage essentially makes them effective at any range, rendering numerous class-specific bread-and-butter weapons such as the Soldier's Rocket Launcher, the Heavy's Assault Cannon, the Engineers Railgun and the Pyro's Flamethrower useless.
Nosferatu The Wrath Of Malachi: The Ancient Chalice is the very definition of overpowered. It kills any supernatural enemy (anything that isn't a gypsy, a dog or a bat) instantly, has a good range, and can hit multiple targets at once. It also makes any boss (except for the Count, who requires a specific way to kill him), even the final one, a pushover, as they all go down after just a few splashes. The only downside is that you have to find troughs of water to refill it, but in the West Wing and Main Castle you start finding those every few rooms.
When you do get one the VSS sniper rifle is one of the best guns in the game (very light, silenced, accurate, can kill most enemies in 1-2 shots, and is the only sniper rifle you can sprint with, and ammunition isn't that hard to find, at least compared to SVD and gauss rifle rounds.)
The Gauss Rifle in Call of Pripyat. It can kill every human enemy in the game, can take down any mutant that is not a Pseudogiant (though it itself can be killed in 2-3 shots from the weapon), and plays No "Arc" in "Archery" as straight asthe game allows After you show Cardan the weapon and retrieve the documents concerning about the experimentation of the gun, he will offer you homemade batteries for 2000 RU each, essentially farming unlimited ammunition for your Infinity+1 Sword.
The FN F2000, H&K G36, USP .45 Compact (and the custom version "March"), the "Storm" (unique OC-14 Groza that fires the common 5.45 ammo), the AS Val (late game at least), Strelok's rapid-fire AK-74, the VSS Vintorez and its custom variant "Tide," and the Armsel Protecta "Eliminator". Getting any of these weapons, however, requires you to either have a small mountain of cash, fight through a bunch of enemies, or get on good standings with a certain faction. Once you do that however, and fully upgrade them, you're more or less set for the majority of the game.
With a little bit of exploring in Clear Sky, you can pick up Scar's Vintorez within twenty minutes of starting a new game. Doesn't quite count as a Disc One Nuke, though, because it's totally broken (having been dropped in the emission) and empty, and you won't be finding ammo for it for a while. Even so, carrying it along or stashing it for later retrieval saves you the cost of the weapon itself. Upgrade it properly and stock up on AP ammo (available from the Duty and Bandit vendors and often available on corpses) and you're halfway set for weapons until the endgame.
Getting the Eliminator is pretty easy under the right circumstances, as well - Vano's mission sends you into the middle of a camp with about twelve bandits in it to pay off his debt. You can pay off the bandit leader (who has the Eliminator) and get mugged on the way out, intimidate the bandit leader (with a high-level weapon) and leave, or just murder everyone. Walking into the leader's office and shooting him in the head, before stealing his gun and using it to fight your way out, is both hilariously audacious and fun.
Certain artifacts in Shadow of Chernobyl fall into this as well. Most artifacts give increased protection against certain types of damage, but at very small amounts and with a prohibitive release of radiation per second (too much to control with vodka or antirad without going broke, making it necessary to pair them with an artifact that absorbs radiation, which will leave you winded or make you bleed for longer when struck). Others don't. The Flash and Moonlight artifacts all give large-scale benefits to your sprint meter (wearing one Moonlight or two Flash artifacts can let you sprint indefinitely so long as you aren't overloaded on weight), and their negative effect is an increased vulnerability to electricity. Electrical anomalies are encountered maybe three times in the entire first game, and actually spawn more of these artifacts. Picking up a handful of Flash or if you're incredibly lucky, a pair of Moonlight artifacts at the Agroprom Underground is incredibly easy and makes it simple to outrun the wildlife and hostile stalkers when engagement isn't an option, and makes shuttling tons of gear back and forth a cakewalk.