This is copied directly from Coldyron's post on hkcentral.net
The Basics
As a pyro, you have two main jobs: ambushing and spychecking. The pyro excels in close-quarters because of the nature of his weapons. The flamethrower can take down a heavy in seconds at point-blank range, the shotgun can kill fleeing enemies , and the fire axe is umm… It has a cool taunt, I guess. You shouldn't be using the axe when you have the flamethrower as a much more efficient killer.
The pyro is not going to win in a heads-on fight, which is why learning the maps is important. Taking a less used path is a good way to be behind the enemies and roast them before they know what hit them. Observe enemy movements, find the paths most of them like to take, and find a different path that will allow you to ambush them.
The Weapons
1. The Flamethrower/The Backburner
Damage range: 187-125 damage per second (500 dps with crits at point-blank range)
The flamethrower is the pyro's primary weapon. It has a very limited range, but deals very high damage throughout the entire range. The trick to mastering the flamethrower is knowing that the flame you see on the screen is NOT the actual flame the server sees. The flames on your screen lag a little, which is why you should lead your flame when trying to burn a fast class, like the medic, scout or other pyro. Your flame is also significantly shorter while moving forward and turning, which can be used to your advantage against other pyros, as I will discuss in the Class Matchups section.
The alternate fire of the flamethrower is the air blast. The airblast is exactly what it sounds like, a blast of air comes out of the flamethrower, pushing back any projectiles, stickies, or people about a foot in front of the pyro. This is useful to push away stickies, push back ubers, and clear a point you are trying to cap/defend. It also can put out fires on friendly classes. It is easily the most versatile tool and one of the funnest weapons to use in the game. It should be used sparingly though, as it uses 25 units of the flamethrowers ammo.
The Backburner is the pyro's unlockable primary weapon. By using it, you are guaranteed crits while attacking someone from behind, but lose the air blast ability of the regular flamethrower. This makes it much easier to defeat heavies/soldiers/demos you catch by surprise, but you lose the ability to be able to try to go head-to-head with a demoman or solider.
2. The Shotgun/Flare Gun
Shotgun damage range: 80-10 per shot (180 with a crit)
Flare Gun damage range: 25-14 (60 with a crit)
The shotgun should mainly be used as a mop-up weapon. As you can see, it has a very high damage falloff. This makes it the perfect weapon to use when your enemy is out of the range of your flamethrower, but is close enough for shotgun shells to have an effect. The shotgun's taunt is also an instant kill on any enemy or enemy building it touches.
The flare gun is an unique weapon in TF2. It is the only one that gains damage the further it is shot. I personally don't have much experience using it, but its primary purpose is to irritate snipers and medics. A medic on fire is almost always going to retreat, and a sniper on fire can't aim. The flare gun requires careful aim and has a slow reload time, so make each shot count.
3. Fire Axe/Axtinguisher
Damage Range: 45-85 (195 with crits)
In my opinion, the fire axe should not be used under any circumstances. The Axtinguisher, on the other hand, can be a very useful tool in the right hands. It does very little damage normally, but when used on an enemy who is on fire, it guarantees 100% crits. This is very useful on slow, high hp classes like soldiers and heavies.
Class Matchups
1. Scout: The scout can be a problem for a pyro, but only if he's smart enough to stay away from your flames. Because of the speed of the scout, the best way to fight one is to try to flame him, and shotgun him while he retreats. FaN scouts are a totally different problem however. If they even graze you with one bullet, you'll go straight up in the air, allowing them to get an easy shot in. Most FaN scouts can't aim, but the ones that can are almost impossible to be killed by a pyro. My advice would be to avoid these guys, they're too much trouble to try to kill.
2. Solider: The solider used to be the bane of the pyro's existence, but the air blast gave the pyro a chance to fight back. You can reflect rockets back at the solider who fired it, hopefully damaging them while staying at full health. Crit rockets can also be reflected, stopping a Kritzkreiged solider in their tracks. A good solider, however, will know to aim at a pyro's feet, making the air blast useless. The most efficient way to kill a solider is still to sneak up behind them and flame them.
3. Pyro: Fighting a pyro can be frustrating, as flames don't do as much damage on them as they do to other classes. Because of the flame lag I discussed earlier, killing enemy pyros can be very easy if you run backwards away from them while flaming and trying to get him to chase you. If he chases you, for a moment, your flames will hit him while his won't hit you. This can make for some easy kills where you barely take any damage. Do not ever chase a retreating pyro because of this. It is better to stay at a distance and fire your shotgun at him.
4. Demoman: The demoman can be one of the pyro's toughest enemies to take down. With a grenade launcher that can take down a pyro in one hit, and stickies that are easily spammed, demomen can be tough to kill. The airblast helps a lot when fighting a demoman. Being able to repel flying grenades and push back stickies is an invaluable tool. Using it can make inexperienced demomen suicide, giving you the kill. Again, the best way to kill a demoman is to ambush him or sneak up behind him and roast him.
5. Heavy: The heavy is one of the toughest enemies for a pyro to kill. He has very high hp, and a weapon that can kill a pyro at point-blank range in two seconds. Taking on a heavy requires some planning beforehand. The best time to take on a heavy is when he is firing at other members of your team. Using them as a distraction, you can sneak up behind him and hopefully kill him. If an enemy heavy ever sees you and starts warming up his gun, the best advice I can give you is to run.
6. Engineer: The engineer by himself is very easy to kill. Your flamethrower does more damage at max range then his shotgun will do to you (except for crits). An engineer's sentry is also easy to kill as a pyro, in the right conditions. If a sentry is right around a corner, a pyro can usually kill it by flaming it while it is rotating to lock on to the pyro. This usually works with level 1 sentries, but the knockback of level 2 and 3's might push the pyro away. Another strategy is to try to circle-strafe a sentry. This will only work if the sentry is in an open area and cannot lock onto you before you can reach it. Circle-strafing can kill all three levels of sentries.
7. Medic: A medic who is healing should always be your first priority. If you can sneak behind a group of enemies without them noticing, you can usually flame their medic if you're careful not to flame any of them. Most people don't pay attention to the health of their medic, giving you free kills. A medic with the Blutslaugher can give you some trouble, but feinting a retreat usually tricks a medic into turning around, giving you a chance to shotgun him.
8. Sniper: Most snipers won't give you much trouble, as they don't realize a fully charged body shot will almost, if not kill you, and snipers don't usually watch the side routes you should be taking. The pyro's weird head makes him hard to headshot. If you have a sniper bothering you, switch to the flare gun if you need to distract him.
9. Spy: The spy should be your most dominated class. You can set a disguised or cloaked spy on fire, revealing his position to your entire team. The spy's revolver is the only weapon that should give you any sort of trouble. If the spy hits you with all six shots, you'll most likely be dead. The best advice I can give when facing with a spy and his revolver is to switch to the shotgun and move in a zig-zag pattern.
