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Basics

Health: 125
Speed: 100%
Primary Weapon: Revolver
Secondary Weapon: Electro Sapper
Melee: Balisong
Additional: Watch, Disguise Kit

Right off the bat you can see that the Spy is the weakest class in a straight comparison to the other classes. This is one of the first things you need to realise, that the Spy is rubbish if you try to play it like a Soldier or a typical combat class. The best analogy I can give for the Spy is to call it a ‘glass cannon’. A backstab is the most powerful attack in TF2, killing any target regardless of overheal, but having such low health and only a revolver makes a Spy easy to kill.

To be successful with the Spy, you need to be able to get in, stab the target and get out – alive. I have another analogy and this is the best way I can describe how a Spy works in a game. Imagine the act of fishing, not in too much detail though. The basic concept is that you cast out the line, then reel it in hoping the fish will bite. Transferring this idea to TF2, you start with your team, use invisibility to get behind the enemy, remove invisibility, apply a disguise and work your way back towards your team taking out any targets of opportunity. When in doubt, think of fishing!

Time to discuss the tools of the trade. Some data gathered from TF2 Wiki

Revolver

Base damage: 40
Critical: 120

Ambassador

Base damage: 34
Critical: 102
Note: Only deals critical damage on a headshot and never gets random criticals.

Electro Sapper

Disables and damages an enemy engineer’s buildings. This item doesn’t have ammunition or a reload time, so it can be used on multiple buildings as quickly as you can click.

Time taken to destroy a structure with no additional damage
Level one: 6 seconds
Level two: 7 seconds
Level three: 9 seconds

Disguise Kit

Allows the Spy to disguise as any class from either team. Disguised attributes like health and player name are mostly random.

Invisibility Watch

Cloak: 10 seconds
Recharge: 30 seconds
Note: Ammunition and dropped weapons restores charge.

Cloak and Dagger

Cloak: Infinite (7 seconds when running)
Recharge: 15 seconds

Note: The drain is motion-based, so staying still gives you infinite charge whereas falling will drain it in around one second. Cannot replenish with ammunition.

Dead Ringer

Cloak: 6 seconds, 90% damage reduction
Recharge: 15 seconds

Note: This watch activates when you take damage and spawns a fake corpse unrealistically so it doesn’t fool experienced players. The Dead Ringer doesn’t shimmer when you take damage or collide with an enemy.

Using the Disguise Kit

As a general rule, you should never be seen as a Spy. Always be disguised, alternating between the appropriate side and classes according to the situation. When you’re in safe territory or with your team, disguise as a friendly class with full running speed (Pyro, Engineer, Medic or Sniper). Don’t ever disguise as Scout because you run really slowly in comparison and the animation is different meaning it won’t fool the opposition.

Once you’re in enemy territory, you want to adopt an enemy disguise that’s suitable. If you’re right at the back of a map, disguise as Sniper. If you’re running around the frontlines, try Pyro. Keep mixing up disguises and try to find a disguise of a player who isn’t nearby. An enemy player seeing a copy running towards him will immediately know you’re a Spy. It’s best not to disguise as slow classes because it reduces your mobility, the only time I’d use a Heavy disguise is to fool an enemy Medic into wasting an ubercharge on me.

Hopefully this is enough for a fundamental basic lesson, I will go into the items, playstyles and other tactics in future tutorials. Remember the fishing analogy and always use friendly disguises in the correct places!