Team Fortress 2/Pyro

The Pyro is the best close combat class in the game. The Pyro's flamethrower will set enemies aflame and cause mass chaos. The Pyro is best used in ambushes.
 * Health: 175 (225 with the Backburner)
 * Speed: 100%
 * Type: Offense
 * Special Ability: Can't be set on fire

Weapons
The pyro's loadout makes him suitable for close combat and not much else. One of his unlocks gives him a bit of long range harassing capability, but that's about it.

Primary Weapons
The Flamethrower is a very powerful weapon, but has a very short range. When you hit a player with the flamethrower they will be set on fire and take a further 50 damage over 10 seconds. A common strategy is to set your opponent on fire and run, leaving your enemy to die by the flames. Keep in mind that your chances of succeeding will be much higher if you catch your enemy off guard, if the enemy knows you're coming you will likely fail. The Flamethrower will obviously not work underwater. Disguised spies will be set on fire if you flame them. A good way to spy-check is to puff some fire into your teammates. If you do set a "teammate" on fire it is a disguised spy, you should proceed to bake him.
 * Flamethrower - Clip Size: 200

The flamethrower's alternate fire will let out a burst of compressed air at the cost of 25 ammo. This burst of air can reflect projectiles, shift stickies and bounce enemy players around. You can use it on ubered people too, try and seperate the enemy medic from his patient or just bounce both enemies away until the uber wears off.

The Backburner is the alternate version of the flamethrower. Although you cannot airblast with it, you gain 50 extra health and, best of all, you get guaranteed crits from behind! This makes the backburner perfect for flanking.
 * Backburner - Clip Size: 200

Remember, that although you become better at ambushing, you lose your ability to seperate ubers, reflect rockets and push people off CPs, so think a little before you take this.

Secondary Weapons
The standard shotgun is the Pyro's standard ranged weapon. The shotgun is an incredibly useful weapon for the pyro, good for finishing off burning enemies, dealing damage while running away from combat, dealing damage while running towards combat and fighting underwater. You should be using the shotgun almost as much as the flamethrower.
 * Shotgun - Clip Size: 6 - Reserve Ammo: 32 - Reloaded one at a time

The unlockable alterative to the shotgun. While this gun does little direct damage, it sets people on fire, making it perfect for long range harassing. Snipers in particular can't aim properly while on fire, so one of your greatest weaknesses, long range, can be somewhat negated by good use of this gun. Unlike the shotgun, though, this weapon is almost useless for finishing burning enemies and it can't even fire underwater.
 * Flare gun - Clip Size: 1 - Reserve Ammo: 15

Taunting with either secondary weapon produces a fireball that deals 300 damage. Normally this isn't much use, but it's good for a humilation kill. Plus, you can use it after your team has lost to score a surprise kill.

Melee Weapons
The Flamethrower is a superior close combat weapon, except underwater. The Fire Axe is great for humiliating people, but can also be useful against other Pyros if you manage to score a critical hit. If you take the flare gun, this will be your only refuge underwater, so you'd better be good with it if you play maps like Well and 2fort.
 * Fireaxe

The axtinguisher is the alternative fireaxe. It does half damage normally, but if the enemy you hit is on fire it crits for 100% damage. This makes it a superior choice in many situations, but if you take the flaregun and this weapon you will barely be able to fight underwater at all.
 * Axtinguisher

Using the Pyro
The Pyro is almost exclusively a short-range class. They can only harass at long range, but their combination of average speed and fair amount of health make them harder to hit than Soldiers or Heavies and tougher than Scouts or Medics, and so able to avoid much hassle from Snipers or Soldiers firing rockets and able to withstand the miniscule damage from a long range minigun. Usually, the Pyro should try to get toe-to-toe with enemies as much as possible, since that's when the flamethrower is most damaging, and ambushing enemies by coming up behind them or dropping off a higher ledge often works very well. Remember though: Don't go point blank with Soldiers or Heavies unless you're certain you can pull it off. Point blank, the minigun rips you to shreds so unless you get a string of crits (backburner is good for this), it's best to light and run.

Two pyros working together do far, far better than combos such as dual demoman. One pyro can light enemies up while the other hits them with the axtinguisher, two pyros with the backburner trapping an enemy in a sea of crits or one pyro can blast an enemy straight into an ambush spot.

Offensively, a Pyro is a very effective anti-Scout class. Heavy/Medic combos can be taken down easily too, if the Pyro hides and then runs straight at the Medic and is careful not to hit the heavy, often the heavy won't notice his medic has died until it is too late.

The afterburn of the Pyro's flames also means that you can set enemies on fire, toast them for a bit, then run off and let the burning finish the job. This works well against low-health classes like Medics, Scouts and Spies (although not that well against Soldiers and Heavies). If you are under threat from enemy Spies, a paranoid Pyro who goes around trying to burn everyone on their team (assuming friendly fire is off) is a good way of rooting out disguised spies, since they catch fire and will continue to burn whilst cloaked, revealing them as an invisible blur surrounded by flames.

Pyros are also effective against enemy Pyros. Their flame-retardant suit means that although they can take damage from fire, they don't actually burn, and a skilful Pyro can take out an enemy Pyro with little trouble and shrug the flames off afterwards.

Defeating Pyros
Unless you have another close-range weapon like the rocket launcher or minigun and have a method of healing nearby, close-range assaults against a Pyro will likely result in your death. Staying outside the range of the flamethrower whilst continuing to attack an enemy Pyro works far better, since the range of the flamethrower is very short and many other weapons continue to be effective outside that range.

Good aim as a Sniper also helps; Pyros don't move as quickly as Scouts or Medics but they are still quite fast, but susceptible to Snipers if they can aim well. Soldiers or Heavies grinding them down from a distance also works. Basically, to beat them, stay out of the flames. As outlined before, Scouts and Spies are generally at a disadvantage when it comes to Pyros.