Don’t turn invisible and think you’re invincible: they’re completely different words. Don’t go running after the person you’re disguised as. Don’t try to backstab somebody in the front or while surrounded by a dozen other enemies. Don’t kill an Engineer if he has an operational Sentry nearby. Don’t think you can replace a Heavy and destroy the other team with L’étranger. Basic advice for budding Spies, wouldn’t you think? But like that Sniper who tries to shoot through glass, there doesn’t seem any end to the ignorance of newbie Spies.
Now if you’re new to TF2 and you like the Spy, I don’t blame you. Some people prefer sneaking around and eliminating particular targets, rather than full-on explosive combat. Nothing wrong with that. It’s just that Spy is a specialist support class, like the Sniper, so it takes a lot of practice to master his unique abilities. After becoming familiar with the more common mechanics of the game, that is.
As a Spy, you’ll be using your tricks to take on the various other classes in the game. Some, like the Pyro, are able to easily detect Spies and kill them before they do any damage. Others provide worthwhile targets if getting rid of them allows you to access an objective. In particular, the Engineer and his buildings are vulnerable to a good Spy. It’s worth dealing with an Engineer for the benefit of your team, as a well-placed Sentry or Teleporter can bring your assault to a standstill.
Your disguise kit enables you to take on the appearance of any enemy player and, with the invisibling watch, can get you deep into enemy territory. Once there, what should you do? It’s tempting to try and backstab as many of the opposition as possible, but that is not recommended. Once you let loose with the knife, your disguise drops and reveals the suited Frenchman, whether you’ve made a kill or not. Some people don’t seem to realize this fact; if you’re one of them, pay attention. When the white outline of a Spy flashes up, it means your disguise is lost.
When a Spy suddenly appears in the midst of his enemies, he’ll be toasted or blown to bits even if he tries to escape with the aforementioned watch. This is why a direct assault by a Spy is considered suicide. So don’t try it! Only backstab when you know you can make a successful kill and your target is isolated from their friends.
Now, the Engineer. Your Sapper is specifically designed to be attached to his buildings and drain them of health. It isn’t technically a weapon; the game considers Sappers as buildings with a certain amount of health. That’s why they can be smashed by melee weapons. Be cautious; a good Engineer will never leave their buildings unattended for long and will be prepared to defend them. Even worse to be disguised as the very Engineer you’re targeting; the chances of having two Engies on the same map with the same username and loadout are very small indeed. Better to disguise as a Soldier who needs the Dispenser for ammo.
What’s even worser is if you try to backstab the Engineer BEFORE sapping his Sentry. Once your disguise drops, said Sentry will be onto you like the devil’s pet limpet. If you’re quick enough you can place a Sapper and kill Engie before he has a chance to knock it off. A Sentry in the process of being sapped can’t shoot you. But newer players, be careful!
Basically, there is a lot new players keep doing wrong with Spy. I hope this article has provided a bit of useful advice, but the most useful thing I can say to you is to check out the Team Fortress 2 Wiki and have a look at the ‘Tactics’ pages there. There’s an awful lot to learn when you’re just starting out. And always practice! We’ll make a Spy out of you yet.