1. The Kritzkrieg (Medic)

First released in 2008 during The Gold Rush update, the Kritzkrieg is an alternative to the Medi-Gun that has a faster-building Uber-Charge that grants critical hits instead of invulnerability. The pros and cons of trading invulnerability with deadliness is a tactical choice that makes the Kritzkrieg a must-have and a definite game-changer.

2. The Flare Gun (Pyro)

Released a few months after The Gold Rush update in The Pyro Update, the Flare Gun changed one of the Pyro's core limitations - being a short-range damage dealer. While not an incredibly powerful weapon; the weapon does crit when victims are already on fire, the Flare Gun gave the Pyro the ability to deliver fire-damage across long distances and become a major Sniper deterrent.

3. The Axtinguisher (Pyro)

Another Pyro Update entry, The Axtinguisher immediately became a must-have weapon - and is still a necessary tool for the Pyro. It deals critical damage to enemies who are on fire - 195 HP - enough to kill almost all classes in one blow. This meant that Pyros could set enemies on fire, and then quickly eliminate them with The Axtinguisher - the deadliest tactic for Pyros to-date. It's such a deadly weapon, and that makes The Axtinguisher a game-changer.

4. The Sandvich (Heavy)

The Heavy Update hit in the August of '08 and with it came The Sandvich. Less useful at the time, and better for making Om-Nom-Nom noises - The Sandvich today is an understandable trade-off for the Heavy's trusty shotgun. Bringing the Heavy to full health over the course of a taunt animation - The Sandvich can be risky - but sometimes no less risky than a slow, low-health Heavy looking for a Medic or Health Pack.

5. The Cloak and Dagger (Spy)

The Sniper vs. Spy Update of 2009 brought a lot of new weapons and tools for some of the more notorious classes of the game. The Cloak and Dagger, a new cloaking system for the Spy was one of the more significant changes to how the Spy could played. Instead of relying on picking up metal to stay cloaked - with the Cloak and Dagger a Spy simply had to stand still - and the cloak would last forever - even recharge. The Cloak and Dagger added new deadly Spy tactics and increased the success rate of existing tactics and is my final "game-changer".

I think giving Demoman melee weapons and making him almost completely explosive obsolete was quite a big changer.

I think the Dead Ringer is far more game-changing than the Cloak and Dagger myself.

@valrog said:

I think giving Demoman melee weapons and making him almost completely explosive obsolete was quite a big changer.

I love running a melee specced demoman but I suck sooo bad at it. It's difficult as hell.

Instead of relying on picking up metal to stay cloaked - with the Cloak and Dagger a Spy simply had to stand still - and the cloak would last forever - even recharge. The Cloak and Dagger added new deadly Spy tactics and increased the success rate of existing tactics and is my final "game-changer".

@valrog said:

I think giving Demoman melee weapons and making him almost completely explosive obsolete was quite a big changer.

Oh yeah. I was thinking about this before - I remember in the weeks following the War! Update the servers I played on being full of Swordsman-Demos. Now and days though, don't you see a lot more oldschool Demos? At least for me, its something like 1 in 3 demos I see is using the Charge-N-Targe & Melee Combo. @Darksaw said:

I think the Dead Ringer is far more game-changing than the Cloak and Dagger myself.

How so? I don't have any experience using the Dead Ringer but, it seems like everyone picks up on the fact that a Dead Ringer spy is nearby thanks to the loud noise it makes. It seems to make people more aware of the spy's presence and most of the time it seems like the spy dies.

The flare gun really isn't that big of a deal. The equalizer and Blackbox on the other hand.

I love the Flare gun. It is a serious counter to Snipers and can be used to repel enemies from long distances. I mostly pick the shotgun over it, simply so I can fight underwater if I have to.

Infinite rocket launcher in RE1

Infinite rocket launcher in RE1

Im pretty sure the razorback and the force of nature are far more game changing then most of this list.

My primary class is Engineer, so the introduction of the Gunslinger was easily the biggest game-changing weapon for me. It really allows you to play in a more offensive capacity, especially when paired with the Frontier Justice, while not limiting what I consider the Engineers main role- teleporters and dispensers.

interesting that you didn't include the eyelander/targe combo, completely changing the basic tactics of an entire class

DemoKnights changed the game for me.

As someone who plays Pyro a lot... the Flare Gun isn't a gamechanger at all. The standard shotgun is still far more useful in most situations.

On the subject of the Dead Ringer, it's much better than the Cloak and Dagger. The C&D's faster drain forces you stop more, and reliance on standing still to recharge and not find metal encourages horrible Spy habits. A Spy should be memorizing level layouts, locations of metal and health, and easy routes for stabbing valuable targets to harass a push or defense, not standing still and waiting for targets of opportunity to wander through a tunnel. A C&D in the hands of a good Spy can good, but the DR changed the game far more. The fact that a Spy might not be dead after you "killed" them added a whole new layer to the game.

Dead ringer so far seems pretty killer. There was this one spy.....

DEMOKNIGHT! THE 10TH CLASS!

@UnrealDP said:

Im pretty sure the razorback and the force of nature are far more game changing then most of this list.

I'd argue pretty heavily against the Razorback; if only because a Spy can still get the upper hand by sneaking behind a Sniper (shoot the head) - having used the Razorback myself a bit - I will say it eases my fear of Spies.

The Force of Nature is no doubt an important tool for Scouts, but I think its very balanced with the original Scattergun.

As for the whole Demoknight thing, I guess it goes to show the unique TF2 experiences that exist on different servers - I believe in the drastic changes in gameplay you are all telling me about - and it came to mind while I wrote this blog - but I personally have not been affected by Demoknights in gameplay in a way that strikes me as game-changing in the ways that the 5 weapons I wrote about have.

The Deadringer on the other hand now, I'm starting to come around on - I feel like almost every spy I kill is carrying one - but the Deadringer hardly ever saves their lives which is why I didn't write about it.

I would definitely mention the Dead Ringer. Ever since the Dead Ringer was introduced, every time a player kills a Spy, he has to be prepared to face the possibility that he might have to kill him again – and in my experience, every second Spy uses it. Essentially, everyone has to change their tactics by looking around after popping a Spy to make sure the rascal is actually dead. I think this is a bigger game changer than the Pyro's Flare Gun, certainly.

The gravity gun.
 
EDIT: Oh fuck, didn't see the category this thread was placed in.
 
The game changing weapon is most certainly the zapper. Getting rid of turrets changes the tide of any battle.

Id say one of the biggest game changers thats not really a new weapon, kinda sorta, was the Pyro's airblast.

The game changing weapon is most certainly the zapper. Getting rid of turrets changes the tide of any battle.

The flare gun really isn't that big of a deal. The equalizer and Blackbox on the other hand.

Game changing? I would have to say Dead Ringer is more game changing than the C&D. Need to kill a spy twice, and when you have a Big Earner, then it's even worse. I would also say that the Demoknight items are also game changing making the demoknight crazy in melee. If they have the ammo to health one, it's almost rediculous. Pre-nerf sandman also, was very game changing when it used to be able to stop ubers. I wouldn't call the gunsligner game changing, but it definitely does mix the engineer up a lot and makes maps where you might roam solo more dangerous (so anything not PL).

If anything was a game changer for the Pyro it had to have been the Degreaser. This weapon has opened up the possibility for regular joes to be an axtinguishing killing machine, and has helped the Pyro be somewhat of an offensive class.