Team Fortress 2 has enough items believed to be a Game Breaker that it needed its own page. Usually each item is nerfed when the programmers realise what a gamebreaker it is.
Due to the vast range of player ability and sizeable fandom found with TF2, expect the usual Fan Dumb bickering over what is/isn't true about everything.
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First off, the Sandman, introduced in the Scout update. This unlockable replacement for the bat tosses a baseball that stuns the foe (and until an update several months after its release, even in ‹berCharged state) for up to 8 seconds (the farther away you launch the ball from, the longer the stun duration). And after stunning someone, you can pick up your ball (or someone else's) and use it again. It became the first weapon in the game to be banned in league play. In fact, the Sandman caused so much controversy that Valve has nerfed, then buffed, then nerfed it numerous times. Seriously, look at how many patches have been applied to it.
The Scout's Mad Milk was this for quite some time. Anybody hit with milk became an instant HP replenishment sink for anybody who had the common sense to shoot at them, since any damage done to a milk-covered player would return 75% of that amount as health to the attacking player. This meant that if you had a high enough damage output, you could essentially heal yourself about as fast as a Medic can, without the Medic. Thankfully, this was later toned down to a more reasonable 60%.
The Baby Face's Blaster is considered this due to having a large upside and almost meaningless downsides. The reduced speed is still faster than a Medic with the Overdose, and it only takes one max damage hit to get maximum (173%) speed. You can single jump without losing boost, and you are still faster than normal after a double jump. The reduced clip is the only downside in practice.
The Pretty Boy's Pocket Pistol gets a fair amount of hate for stepping into "pure upgrade" territory. Simply equipping the Pocket Pistol gives a Scout +15 max health and prevents him from taking fall damage, greatly increasing his survivability against most other classes. In exchange, it makes him considerably more vulnerable to fire damage, and has a slower rate of fire than the stock pistol. While as a weapon it's rather weak and the extra fire damage weakness dangerous in close-range maps, the frustrating part is that there is no visual indicator that a Scout has an extra 15 health (compared to the Sniper's Darwin's Danger Shield or Engineer's Gunslinger, which are easily visible.) Because of this, many blows that were expected to kill that pesky Scout merely give it an extra chance to flee, grab health, and return, or even to finish you off the next second.
The Equalizer was quite controversial among many circles before its nerf. As the player lost more and more health, he started moving faster and dealing more damage while it was the active weapon, meaning that it became quite possible to one- or two-shot three or more enemies in a period of a few seconds, as the damage let you kill almost any class from full health in two hits and the speed made you nearly impossible to hit. The flip side is that Medics can't heal you while it's the active weapon, which is easily remedied by taking out any other weapon, but when you're moving around so quickly and dealing so much damage, why would you want to be healed? As a melee weapon, it was limited in how game-breaking it could be, but most players considered it a pure upgrade over the regular shovel, and Valve spent several patches nerfing it, finally culminating in splitting up its speed and damage attributes into two different weapons, with the speed portion going to the Escape Plan.
The Escape Plan was nerfed even further due to players still frequently using it as a scot-free escape mechanism whenever a fight went the wrong way. Now, having the Escape Plan deployed causes the Soldier to take Mini-Crit damage as long as he's holding it, and for a short while after you switch weapons, making it tougher to make daring getaways.
The Soldier's Battalion's Backup was also this for a time, though for different reasons. You charged it up by taking damage from enemy attacks, and once you get to a certain point, you just let it loose and any teammates close by become immune to critical hits (including headshots) and got a 35% damage resistance buff. By itself, this wasn't so bad since the effect only lasted for 10 seconds or until the Soldier died (and smart players always target banner-wielding Soldiers as high-priority targets), but the Soldier only had to take 175 damage in order to fully charge it; given that the Soldier has 200 HP by himself, and even more given Medic support or by using the Black Box, it virtually guaranteed that a Medic-backed Soldier could have an active banner going around 50% of the time. In addition to this, fall damage still charged the banner, so it was possible to charge the banner during setup simply by rocket-jumping repeatedly just outside of spawn. The damage requirement was doubled to 350 damage later, though, and various methods of self-charging were also removed, though map effect damage such as burning torches and drowning still charged the banner before its charge method was changed altogether to dealing damage rather than taking it.
Ironically, the damage absorption nerf ended up producing an inversion of this trope, namely that it was so high that players didn't want to take the risk of absorbing 350 damage without dying just for some minor buffs, so Valve changed the weapon to make it charge through dealing damage. They also buffed it so that the boost has an additional 15% Sentry resistance, causing Sentries to deal only 50% of their normal damage to players that have been boosted with this weapon.
Upon initial release, the Cow Mangler 5000 was quite unbalanced. Besides dealing reduced damage against buildings and its inability to be crit-boosted, it had no drawbacks compared to the stock Rocket Launcher; however, it has unlimited reserve ammo AND 5 shots per magazine instead of 4, allowing Soldiers to do huge amounts of damage while away from support, and its damage ramp-up was unintentionally too high, meaning that it did more damage than the Rocket Launcher at close range. On top of all this, it has a special charge attack that lands a guaranteed Mini-Crit (which also sometimes did more damage than normal on top of the increased ramp-up), ignites players hit by it, and disables Engineer buildings for 4 seconds; this allowed Soldiers to disable Sentry Gun nests from a distance without the need to get a Spy close-in, and possibly kill the Engineer tanking it. Then there was the fact that it was a literal game breaker in that its particle effects taxed some graphics cards beyond their limits. Virtually all of this was fixed shortly after the update that introduced it, although later some of its penalties and bonuses (the extra shot per magazine and reload/damage penalties) were removed.
The Beggar's Bazooka gets a fair amount of hate for its ability to quickly fire off three rockets, which makes it difficult for Pyro's airblast counter and gives it immense Sentry destroying power. However its poor long-range accuracy, that each shot has to be loaded manually before firing, and that the wielder must keep his aim steady so the rockets don't go all over the place is a good counter to this feature. It was one of the Beggar's Bazooka's supposed drawbacks that really brought it into game breaker territory. If you load more than three shots into the Bazooka the weapon would misfire, causing damage and knock back. If you jump while this happens you will rocket jump, however you can keep loading rockets into the weapon which will keep causing it to misfire every time. This allowed for the soldier to midair rocket jump repeatedly, or, in layman's terms, FLY. Fortunatly now a misfire will also remove on rocket from the magazine and deal more damage, which increases the iteration between explosions and increasing the difficulty of flying.
The Valve Rocket Launcher is an intentional game breaker. It's overpowered to a crazy level, with immense damage and rocket speed, on top of healing the user and giving them critical hits for every kill. The Valve Rocket Launcher is only available to TF2's director Robin Walker, who uses only when requested and then merely for trolling opponents, not to constantly win matches. There were once other Valve weapons with various other overpowered traits, but all of them but the Rocket Launcher have since been deleted.
Ironically, its overpowered status was temporarily negated by the pre-nerf Short Circuit, as its firing rate and minimal metal consumption could let an Engy completely negate every Valve-rocket. Since then it's been twice nerfed so the Valve Rocket Launcher once again reigns supreme.
The Pyro's Phlogistinator was a fairly controversial weapon. In exchange for having no airblast, Pyros gain a "Mmmph" meter that tracks how much damage the weapon does. Once it's built up enough, they may activate a taunt that gives them guaranteed critical hits for 10 seconds, while restoring them to full HP. Normally, this wouldn't be too bad, but for the duration of the taunt, the Pyro gained 90% damage resistance, essentially making them invulnerable. This allowed players to stop in the middle of the battlefield and taunt without any repercussions until after the taunt finished. Additionally, the required fire damage in order to activate the taunt is a mere 225 points, which is easily achievable (just kill one or two enemies and ignite a couple others), and the critical hit boost is longer than the Medic's Kritzkrieg ‹berCharge. On top of that, since fire damage wasn't limited to igniting enemies with the Phlogistinator, using a flare weapon could guarantee that you would have a full meter before even getting within flamethrower range of an enemy. In addition, "Mmmph" gained from fire damage was not affected by fire resistance; for example, a Spy equipped with the Dead Ringer (see below) could completely fill the meter despite not having enough health to do so normally. Thankfully, Valve toned this down over various patches, culminating in reducing its damage reduction to 75% and reducing the critical hit boost to 10 seconds.
The "Puff and Sting" combo was a very controversial moveset for the Pyro requiring both the Axtinguisher and Degreaser. The Axtinguisher guaranteed crits on its melee hits if its target was on fire, the Degreaser reduced the time to switch weapons. This meant that Pyros could kill any non-overhealed class minus Heavies in less than 1.5 secondsnote The Degreaser takes 0.4 seconds to ignite and 0.23 seconds to switch weapons, the Axtinguisher's attack time is 0.8 seconds. Allowances may be made for player reaction time and speed of button pressing. by igniting their target then quickly stabbing them with their axe for a critical hit kill. Proponents of Puff-and-Sting argued that it was balanced because the attack is very short-ranged, and because the Pyro is an underpowered class overall. Opponents to it argued that it was nearly impossible to fight back against once one was in range, diminished the role of fire, and that Pyro's airblast further increased Puff-And-Sting's juggling and trapping capabilities. Valve eventually toned down Puff-and-Sting's effectiveness by having the Axtinguisher deal crits from behind but mini-crits from the front, encouraging Pyros to ambush for crits.
For the longest time the Demoman as a class was considered a gamebreaker, as on top of being the only character with true indirect fire, he had the mobility of a Soldier but could also rapidly spam his grenades and stickies, whereas the Soldier could only fire off 4 rockets before a lengthy reload, allowing a Demoman to kill any class he sees before he needs to reload. Also unlike the Soldier, the Demoman's normal walking speed only has a 7% penalty (as opposed to the Soldier's 20% decrease and the Heavy's 23% decrease). All of this combined meant that a Demoman had no real weaknesses, making the only way to counter one to either catch him off guard or play a demo yourself. The Demoman's Grenade Launcher would be later nerfed to only 4 grenades in the magazine instead of 6, and the Stickybomb Launcher's ammo reserves reduced from 40 to 24.
The ability to detonate sticky bombs in the air was later also toned down — while still a viable tactic, any sticky inside a certain radius to the Demoman that had been launched in the past five seconds or so suffered damage falloff. Later, stickies were altered so they only reached max potential damage after being primed for two seconds. These changes were placed to limit airburst sticky bomb spam. Previously, a Demoman could quickly fire, then detonate sticky bombs in the air at mid to long range to dish out damage. However, much complaint from the competitive gaming community led to the nerf being reverted a week later (airbursting stickies while advancing is a common offensive tactic), though Valve promised to continue examining the issue and balance the sticky launcher some other way.
The Sticky Jumper, a Joke Weapon intended for training how to sticky-bomb-jump quickly proved to be a Lethal Joke Weapon in the right hands. While it deals no damage, and initially had a damage taken and max health penalty, Demos using it can fly through the map so quickly that it is nearly impossible to hit them. Additionally, it replaces the secondary weapon of the Demoman, compared to the Soldier's Rocket Jumper which replaces his primary weapon. As such, a Sticky Jumper Demo still has a major source of firepower retained, and could quickly make a mockery of game modes like Capture The Flag. A glitch was also present that made the player immune to self-damage from other weps, removing the primary drawback of the Ullapool Caber combined with the ease of flying back to spawn to replace each caber. Valve eventually blocked players from carrying the flag while having the Sticky Jumper equipped, reactivated self-damage from other weapons, then reduced the amount of active stickies usable at one time from eight to two, reducing Demos' flight distance.
The Tide Turner, released in the Love and War update. It gives FULL control over your shield charge while occupying the secondary slot, allowing a Demoknight to keep his grenade launcher yet turn like who has equipped the Bootlegger/Wee Booties. Worst of all, it completely recharges your charge meter if you charge-crit-kill someone. Putting it simply, if you know how to play Demoknight effectively, then you can VERY easily chain-charge everyone. Add in combos with the Half-Zatoichi (which refills your health upon a kill) or the Eyelander (which increases your max health and speed based on kills) and Demoknights can become basically unkillable to all but Sentries.
Natascha was highly controversial for a time. In theory, it was supposed to be weaker because it did less damage per bullet than Sasha, and its "slowdown" effect was meant to make it a support weapon that made it easier for teammates to hit people you were shooting at (or for you to land more bullets on them). In practice, the slowdown effectively became a tractor beam, making anyone that been shot ONCE, regardless of distance, become a statue, allowing even more shots to be landed. Thus, the second weapon to be banned in competitive leagues. The Australian Christmas update tweaked the slowdown so that its effect would be reduced at long range, and increased its spin-up time so that Natascha-wielding Heavies were easier to ambush.
The ‹ber Update gave the Heavy the Tomislav, a minigun with a silent and fast spin-up that does slightly more damage than Natascha. In effect, the faster spin-up time turned the Heavy into the most powerful ambushing class in the game, even moreso than the Pyro, who was designed specifically for ambushing enemies, because the slow spin-up time and the loud whirring of the Minigun's barrel were supposed to be the Heavy's greatest weaknesses. Immediately after the update hit, Heavies could sneak up behind their enemies and mow them down effortlessly, to the point that the reduced damage output didn't matter at all. Another problem was that since it spun up faster, the slower firing speed didn't matter at all since the time saved spinning up could be used to kill most weaker enemies faster (which makes a large difference in the case of a Medic) versus the regular Minigun. So trying to sneak up on a Tomislav Heavy to perform an ambush was futile, since they could turn around and mow you down half a second after you land your first hit. A patch which lowered its spin-up time reduction from 75% to 40% somewhat rectified this, and an additional patch almost completely eliminated the spin-up bonus.
The Gloves of Running Urgently, originally released in the Polycount Update, gave the Heavy unprecedented mobility for virtually no penalty. While it was the active weapon, the Heavy lost 6 HP per second, but had his movement speed boosted to match that of other classes, allowing him to keep up with teammates and move to the front lines much more quickly. The health penalty was originally intended to penalize the Heavy and force him to work with teammates, especially Medics, in order to maximize its usefulness, but when combined with the Sandvich's ability to instantly heal, this penalty suddenly became useless, and Heavies could additionally simply equip the GRU and make a fast getaway for no penalties if a fight turned the wrong way. In addition, the health drain could be exploited to effectively provide a very small Double Jump, slightly increasing jump distance even more than the increased running speed already did. The health drain penalty was eventually replaced with taking Mini-Crit damage while the weapon was active and for 3 seconds afterwards, forcing Heavies to utilize them more strategically.
There was a way more important issue with the GRU than damage-boosting and recovering health with Sandviches. If a Heavy were to jump and switch away from the GRU, he would retain his running speed until he landed, without being subjected to the full health drain. Many players would use scripts to automate the process of GRU-hopping with perfection, effectively allowing them to reap the benefits of the speed boost with none of the disadvantages. Coupled with a pre-patch Tomislav, the main disadvantages of the Heavy himself were effectively nullified. The Mini-Crit debuff was added to circumvent this exploit.
The Heavy's Sandvich was somewhat overpowered for quite some time. One of its functionalities that was added some time after initial release was to use alternate fire that allowed the user to throw it down and have it act as a medium health pack. Not broken on its own since it encouraged players to share their food with their teammates, but this also applied to the Heavy who threw it, allowing him to heal 150 health nearly instantly, which made it virtually impossible to kill a fleeing Heavy (or one wounded inbetween engagements) since they could throw down their Sandvich and instantly replenish health on the move. Combine this with the Gloves of Running Urgently, and you suddenly have a very mobile Heavy that can get to the front lines for negligible penalties. The devs later removed the self-healing feature, only allowing a Heavy's teammates to pick up the Sandvich for health, while the Heavy must physically eat it in order to regain health.
The Fists of Steel when first released. Sure, you take double damage when hit by melee weapons (usually resulting in OHKO when engaged in melee battle, especially against a Pyro with the Axtinguisher), but the fact that it provided 60% damage resistance against ranged weaponry allowed Heavies to survive fully-chargedheadshots, as well as Sentry barrages. Thankfully, this was later reduced to 40% and a weapon switch time penalty was implemented as well.
At one point, it got bad enough that a Heavy equipped with the Fists of Steel, while backed by a Medic, could wade into Sentry Gun fire on Capture the Flag maps, grab the Intelligence, and simply waltz back out, as the combination of overheal and damage resistance meant that the Heavy had a total effective HP of over 1100, and was being healed for effectively 60 HP/second, just under the fastest rate at which a Medi Gun can normally heal players. The same thing could be done with carts on Payload maps, completely shutting out most push or defense attempts, with exceptions such as an Axtinguisher-wielding Pyro.
Things got hilarious when a glitch was discovered, where disconnecting from the server after playing the Amputator (which gives a small amount of healing to everyone in the Medic's radius) would cause the healing effect to stay. Combine it with the Fists of Steel, and it was possible for a Heavy to wade into point-blank minigun fire and punch the enemy Heavy to death without dying.
The Engineer Update set a new standard for turtling. One of the Engineer's new weapons was the Wrangler, which allows an Engineer to take personal control of where his Sentry Gun shoots. Not bad by itself, but consider the fact that this gives the Sentry infinite range (along with the fact that it has no damage falloff, meaning it does full damage at any range), and among the Wrangler's features is that it doubles the Sentry's fire rate (which is basically double damage), and projects a shield that causes it to take only 33% damage, tripling its HP. With no downside apart from disabling the Sentry for three seconds when the Wrangler is un-equipped or when the Engineer is killed. Instantly banned in competitive play.
Among the new features in the same update is the ability for an Engineer to pack his buildings up and move them. Not too bad by itself since it's generally a wise idea to be able to move Dispensers and Teleporter Exits forward as your team advances. But when you can move your Sentry Gun as well, and combine it with the Wrangler... you can take over and lock down an entire area given about six seconds of nobody noticing you.
The Engineer can also use the Sentry's knockback to shoot himself into otherwise unreachable locations with the Wrangler (called Wrangler-jumping or Sentry-jumping) and set up nigh-impassible choke points, especially not when supported from traditional Engineer campsites by other Engineers. Additionally, some of these places could still be built on prior to some major map overhauls, so was possible to build a Teleporter Exit that cannot be reached by the enemy team.
Eventually, Valve decided to make long-range Wrangling less effective by reducing its long range accuracy and increasing its damage falloff, while reducing the after-deactivation shield duration from 3 seconds to 1. This made it easier for Snipers to simply pick off the Engineer, and then have plenty of time to destroy the Sentry since it wouldn't resist two-thirds of the damage dealt to it.
The Gunslinger is banned on some servers because of its perceived overpoweredness. It replaces the Engineer's wrench with a robotic hand and instead of his giant Sentry lets him build a tiny Mini-Sentry. This Mini-Sentry has a lower damage-per-second and health than even a Level 1 Sentry and can't be repaired or upgraded. So what makes it so powerful? Its tiny size. The usual anti-Sentry classes like Heavies and Soldier have trouble against Mini-Sentries because of their negligible accuracy, having to compensate with a wide area of damage. Against a tiny Mini-Sentry they can't land enough hits on it unless they get closer, which allows the Mini-Sentry to get more hits on them. Combine this with its 3 second deployment and low metal cost, and you find yourself struggling to break a Mini-Sentry only to find the Gunslinger Engy deployed another just after you destroyed the first. Things weren't helped by various bugs that let sentries heal themselves while doing their construction animation, or the one that let it become a Level 3 mini-sentry. Valve eventually patched all the bugs, and increased its hitbox to make them easier to destroy.
The Pomson 6000 got a lot of hate for its low risk vs. reward and capability to easily counter two of the Engineer's counters upon release. Its normal attributes weren't anything to write home about, and its ability to penetrate targets was only really useful when holding down a corridor due to its mediocre damage at long range. The main problem came from its ability to strip 10% ‹berCharge from a Medic for each shot landed; just hitting a Medic twice (which is really easy to do given the projectile's large hitbox detection) was enough to set their charge time back by 16 seconds, long enough to create a window with which to kill the Medic while he's helpless; this becomes a major problem when a Medic has a full ‹berCharge meter, charges forward, only to have it taken away the second before he's able to pop it, completely shutting down a push attempt. Teammates trying to body-block these shots, the natural tendency when trying to protect a Medic, were also wasting their time, given the Pomson's ability to penetrate targets. The Mann vs. Machine update removed its penetration ability, greatly reducing its spammability.
The same weapon also made Spies ineffective. While it didn't affect Cloak and Dagger Spies (although they could be found much more easily simply by shooting everything with a pistol), it heavily affected the Dead Ringer Spy. The Dead Ringer can only activate upon a full cloak, so being glanced by one shot meant you had to wait several seconds before you could actually cloak. A sharpshooter Engineer could hit potential Spies long before they realized what had happened and deny them fake deaths in enemy territory. It also didn't help that the Pomson made a tell-tale noise whenever it drained Cloak or ‹berCharge, whereas every other hit-related sound in the game is disabled if you hit a disguised Spy. Suddenly Pyros were no longer needed...
The Short Circuit, a secondary weapon that disintegrates projectiles and does Scratch Damage to enemies when fired. Released as a Deus Ex: Human Revolution promo, it was widely shrugged off as being a gimmick weapon for turtling Engineers, since it had a high metal consumption rate of 36 and piddling damage, limiting it to being used when hugging spawn or Dispensers. Additionally, it took the same spot as the Wrangler, and even with the 2013 Summer Update (half metal cost on hit, full for miss), it still didn't manage to make a dent in its chances. Enter the 2013 Winter Update, which gave it the firing rate of the Pistol, and made all shots cost only 5 metal; now Engineers were running into the battlefield, even in groups, vaporizing enemies as quickly as the Pyro's Flamethrowers, and rendering Soldiers and Demomen helpless by vaporizing their ammo as fast as it was fired.
Due to the fact that the Short Circuit was so powerful against classes that normally counter engineers, and fact that people were abusing a defensive tool to wipe out enemies, the Short Circuit was soon nerfed; a minor patch (1/9/14) increased metal cost for destroying projectiles (to 15 metal) and lowered the damage even further. A second nerf the next month prevents Engineers from gaining metal from dispensers while the Short Circuit was the active weapon, reducing the Engineer's ability to camp at a dispenser and spam the weapon. While the firing rate was still left untouched, these nerfs encourage Engineers to time it on projectiles, especially if the dispenser is not full or there are no ammo crates nearby.
The Sniper's unlockable primary, the Huntsman, also falls into this category for some. You would think that a bow-and-arrow that does less damage than the Sniper Rifle, carries less ammo, has no scope, and is less accurate would be inferior, right? Not if it uses the flamethrower's hitscan box to determine hit detection! Not only is the hitbox for scoring a successful hit on a target at least twice as big as the target when you're using the Huntsman, arrows that fly close enough to the head will score a headshot. Ever wonder why that Sniper that you ambushed from behind was able to suddenly turn around and headshot you at point-blank range? Now you know.
The Machina is this for some. It does an additional 15% damage on a full charge, making it capable of body-shotting anything short of a Soldier or Heavy at full health on a full charge. It has two downsides in exchange: it fires tracers to tell the enemy exactly where you are, and can't shoot while unscoped. If you're camping in an entrenched position where the enemy can't reach you, then neither of these disadvantages matter and the weapon is a pure upgrade over the regular Sniper Rifle. Because of this, the Machina is infamous among some as a weapon for "inferior" sniper players who can't/won't headshot.
When fully charged it also has the ability to penetrate its targets, allowing for multiple head and body shots in one go. While this is obviously rather difficult in practice, it does have its uses in more competitive play where some players will try to body block such shots to prevent them from harming more vital players such as Medics, or in maps where players tend to bunch up in tight groups.
When the Spy vs. Sniper Update came out, the Spy got two new invisibility watches that could (1) let the Spy stay invisible indefinitely, or (2) fake his death and become essentially invulnerable for 6.5 seconds while ignoring the bump-into-reveal-cloak penalty. Not so bad by themselves since they also had significant drawbacks, but at the time of the update, the Spy also got his own taunt kill, which could still be performed while invisible. And killing the Spy mid-taunt could mean nothing. Valve spent several patches fixing these oversights.
The first release of the Dead Ringer let him cancel it immediately. Add the fast recharge and as long as you constantly clicked to keep it active and cancel any faked death, you had about 1200 HP (ten times the normal amount or so). Compare the highest-HP class, the Heavy, with his smashing 300 HP, the Spy was basically immortal until a patch fixed this. Now it drains down to 40% every time you cancel, as well as having a cooldown of sorts.
It was still broken when it started draining at cancel, because you could decloak (loudly) right before touching a big ammo box, and then immediately ready it up again. Combine this with the typical player mentality of "kill enemy > capture objective", and you could take an easy MVP on defense with virtually no kills by just being an unkillable pest near the attacking team's spawn. In particular, Gold Rush stage 2 point 2 was virtually impossible to lose because of the abundance of ammo back near point 1. This was eventually fixed by severely reducing the amount of cloak that can be gained from large ammo boxes while holding the watch in question.
Even despite all that, the Dead Ringer still demanded nerfs, since the feign death feature was abused by bad Spies for the damage resistance. In addition to promoting bad tactics (using it to tank damage rather than fool the enemy), it served mainly to set back the enemy while the Spy has plenty of time to run to a health and ammo pack, even while on fire. In the end, the Dead Ringer was nerfed so that taking enough damage while cloaked will revoke the damage resistance and no-flicker of its cloak, making sure that those useless Spies don't overstay their welcome (a Dead Ringer Spy will now die to a Pyro in about 3 seconds at most.)
The Enforcer was another ‹ber Update weapon that was highly controversial upon release. For a 20% damage increase, its only disadvantage was taking a little extra time to become invisible... something easily negated by using the Dead Ringer, which instantly cloaks regardless. The additional damage allowed Spies to fight on the front lines and deal a surprising amount of damage to pursuers, which completely eliminates the Spy's class disadvantage of not being able to fight back against other classes in a direct fight or when discovered. This got especially terrible when a certain glitch with the Diamondback allowed players to exploit infinite crits with the Spy's primary weapon. However, it has since been nerfed and now has a slower firing speed, only causes the damage bonus when the Spy is undisguised, and can't deal random critical hits.
The Red-Tape Recorder ruined the game for Engineers to the point it was patched the day after its release. Incapable of destroying or damaging buildings, it removes upgrades from buildings, quickly weakening Level 2 or 3 buildings, but slowly un-building Level 1 items into ammo. Despite being a balanced concept, however, Engineers soon realized that it was removing a level once every 1.6 seconds — the exact time it takes to swing the wrench twice and remove it. In other words, countering required an Engineer to swing his wrench at the exact second the sapper was placed, lest he lose a level; even if Engineers synchronized their hits perfectly, the sentry would still be sapped between wrench hits and would thus remain completely inactive until the Spy was killed.
This was alleviated when the downgrade time was extended from 1.8 seconds to 3 seconds, nerfing it somewhat; while the change was completely understandable, the RTR is now frowned upon inversely, widely seen as a direct downgrade to the Sapper. Since the RTR takes 10.7 seconds to finish off a Level 1 Sentry (or even 21.4 seconds for Level 1 Dispensers and Teleporters), the higher probability of buildings being saved means that it's only good for weakening guarded buildings for allies.
The first Polycount Update (along with Australian Christmas) brought this with the advent of 'set bonuses.' Having an entire set of equipment grants bonuses and flaws on top of existing ones. While bonuses and flaws aren't exactly new, what made it game-breaking is that some of these sets didn't come with any flaws at all, meaning that somebody with the item set hat had a pure advantage over someone who didn't (for instance, a player with the Special Delivery set while wearing the Milkman has 25 more HP than a player without the hat, while carrying the exact same weapons loadout). This was eventually rectified by making future sets purely cosmetic or having small enough bonuses that they didn't matter, and the old ones had their bonuses merged into the weapons.
In general, the first set of Polycount item sets drew a lot of hate and ire since they required players to wear a hat alongside the items, and hats are a hell of a lot harder to come by than weapons, both in random drop and in crafting. So, for the first few weeks of the update (and for months afterwards), the only ones who were able to take advantage of the item set bonuses were the ones that either got lucky in item drops or crate openings, were farsighted enough to save up enough Refined Metal to craft one of the hats before the update, or simply purchased the hat from the Mann Co. Store.
And so on and so forth. Every time an update ships, you can be sure that somebody will be complaining that the Metagame has been completely ruined.