Basic Pyro strategy
From Team Fortress Wiki
The Pyro is a moderately tough class that specializes in close range combat and excels at ambushing enemies with his various flamethrowers. The afterburn he inflicts will steadily damage fleeing foes, making him decent at hit-and-run tactics. His compression blast is extremely disruptive and can be used to reflect projectiles, extinguish burning team mates, or forcibly shove enemies around. His flames nullify Cloak and disguises, making him a hard counter to the Spy. While easy to learn, mastering how to properly use his various weapons takes time. A good Pyro will often switch between weapons to maximize damage. At longer ranges, the Pyro is vulnerable to hitscan weaponry, such as the Minigun or Sniper Rifle.
To easily get into range to use your Flamethrower, take alternate paths to ambush your opponents. Circle-strafe around your foes to reduce the amount of damage you take. Do not rely on afterburn to finish off enemies, as there are many ways to extinguish it. If opponents flee, switch to your secondary weapon to give chase. Spy-check suspicious teammates by firing short bursts of flame.
Position yourself for ambushes often to make use of the Backburner's substantially increased damage. Overall, you sacrifice defense for offense; the increased compression blast cost will make it more difficult to disrupt ÜberCharges as well as defend yourself at long range.
The Degreaser's faster weapon switch time is highly versatile. It pairs particularly well with your compression blast; after igniting and airblasting an enemy, quickly switch to another weapon, such as the Shotgun or Axtinguisher, to deal severe burst damage. However, the reduced afterburn damage will not reliably finish off enemies and makes hit-and-run tactics less effective.
Dealing any sort of fire damage when using the Phlogistinator, including that from the Flare Gun or afterburn, will cause your "Mmmph" meter to fill, Instead of the compression blast, using secondary fire when the "Mmmph" meter is full will cause you to perform a taunt that refills your health and grants guaranteed critical hits for a short time. You receive heavily reduced damage while taunting, so you can activate your "Mmmph" both before a fight as well as during one. Because it lacks the compression blast ability entirely, your defensive capabilities are limited and you should focus more on ambushing enemies to deal maximum damage.
The compression blast is a powerful source of utility that can be used both offensively and defensively. Offensively, use it to force ignited enemies into map hazards, out of cover, or into corners, where you can then easily finish them off with powerful weapons like the Axtinguisher. Defensively, use it to reflect projectiles, shove dangerous enemies away, and extinguish teammates who are on fire. The compression blast can even move invulnerable players, such as those under the effects of the standard ÜberCharge.
The Shotgun is your most reliable ranged weapon. Use it to engage enemies at medium range, especially when they retreat out of the short range of your Flamethrower. The Shotgun is powerful and is your weapon of choice against other Pyros, who cannot be ignited.
The Flare Gun fires slow, arcing projectiles that can deal reliable damage to enemies outside the range of even your Shotgun. The Flare Gun deals critical hits to burning enemies, allowing you to finish off retreating foes from a distance. If you cannot safely approach an area, you simply can duck in and out of cover while using the Flare Gun to harass at long range; if you consistently land your shots, you'll be able to deal deceptively large amounts of damage, particularly against immobile targets like a Heavy.
Much like the Flare Gun, the Detonator is useful for harassing enemies that are far away or behind cover. The ability to manually detonate your flares gives you a bit of leeway when aiming and allows you to ignite multiple enemies at once. However, the Detonator only deals mini-crits to burning enemies, making it less effective as a finishing weapon. You can use the explosion to flare jump upwards to unusual locations at the cost of a small portion of health, which helps in accessing alternate routes with which to ambush your opponents.
The Reserve Shooter reduces weapon switch time and synergizes very well with your compression blast; use the airblast to force an enemy into the air, then switch to the Reserve Shooter to deal devastating Mini-Crits. Its reduced magazine size makes it less reliable as a standard sidearm, especially when dealing with enemies at medium range or beyond.
The Manmelter functions similarly to the Flare Gun but has infinite ammunition and a faster projectile speed. However, it does not deal guaranteed critical hits to burning players. Alternate fire can be used to extinguish teammates in place of the compression blast, particuarly useful if you want to conserve Flamethrower ammunition. Each successful extinguishing will cause the Manmelter to store one guaranteed critical hit, allowing it to be used as a strong finishing weapon.
Because you are already fighting at close range with your Flamethrower, you will rarely use the Fire Axe. Use a different melee weapon to give yourself some utility.
The Axtinguisher deals guaranteed critical hits to burning enemies and is arguably your most powerful weapon. After igniting an enemy, combine it with the compression blast to easily reposition and kill him from full health. It pairs particularly well with the Degreaser and its faster weapon switch time.
Use your Flamethrower and Homewrecker to defend friendly Engineer buildings from enemy Spies and their Sappers. Offensively, it will destroy any unshielded building in no more than two hits. Because of its limited melee range, initially approach a Sentry Gun with your Flamethrower before switching weapons.
When fighting alone, use the health granted by the Powerjack to stay healthy. You need not worry excessively about the melee vulnerability; as the Pyro, you hold a clear advantage when it comes to close range combat. Compared to similar melee combat methods using the Axtinguisher, you sacrifice a hefty amount of burst damage in exchange for survivability.
The Back Scratcher is best used when your team lacks a Medic or when you're fighting behind enemy lines, where the increased health gain from pickups will allow you survive better when alone. When concerning interactions with a friendly Medic, the reduced healing rate makes you a poor Medic buddy but allows you to help a Medic build his ÜberCharge at an increased rate for a longer period of time.
At melee range, your primary weapons already deal significant damage and set enemies on fire. Thus, you are best off using the Sharpened Volcano Fragment only in Medieval mode, where it is the only weapon that can reliably ignite enemies.
The Third Degree has no downsides and is a straight upgrade from the Fire Axe. It can deal damage not only to struck enemies, but also to any player healing or being healed by the victim via Medic beams. When targeting a Medic's buddy, you can use this weapon to damage both of them at once, particularly useful if the Medic is low on health or difficult to reach. The Third Degree still only deals damage identical to that of the standard Fire Axe; if the connected targets are within close proximity, it may be more efficient to attack all of them at once with your Flamethrower.
Item set effects
The increased move speed granted by the item set allows you to outrun any class but the Scout, allowing you to position yourself for an ambush or retreat more easily. The slight increase in bullet vulnerability is negligible and does not signficantly decrease your survival time against classes that utilize hitscan weaponry, such as the Heavy.