• do not cloak if you don't have to, it takes 3 times as long to charge as it does to use
• try not to uncloak near people, especially in front of them. while decloaking, your translucent effect is the color of your real team, so disguising as an enemy spy will not help you
• decloaking makes a sound that the other team can hear. probably. it's best to stay behind people and far away when uncloaking, even if they can't hear the sound.
• if you are cloaked and you bump into an enemy, you will appear translucent and your team's color for a brief period of time. if you are shot while cloaked, you will also be visible in the same manner.
• if a pyro lights you on fire, you will glow with your team's color and be on fire. You will still be cloaked, but.. you're very obviously on fire and very obviously a spy. AVOID PYROS LIKE THE PLAGUE.

• Avoid disguising as your target. This will be explained a few points from now.
• note that if the class you are disguising as is slower than you, you will be made slower.
• When disguised, the weapon you are holding is always, always, always the default weapon of the class you are disguising as (the one the class spawns holding.)
• When disguised, your name will be that of a random player of the class you are disguised as. If there are none, it will be a random name from the opposing team. (I am not sure about friendly disguises.) This is why you shouldn't disguise as your target, as if they see you with their name they will obviously shoot you.
• if you are cloaked and disguise, the enemy can see the smoke.

The Electro-Sapper is a device that you can plant on enemy engineer structures by clicking on them. It has no cooldown time and does not undisguise you when used. When attached to a building, a sapper will slowly drain its health and then eventually kill it. A sapper can be removed by two whacks from an engineer wrench. Note that while a sapper is attached, engineer whacks will not heal the structure. This is why sapspamming can be effective. Also... EVERY TIME AN ENGINEER KILLS A SAPPER, THEY GAIN POINTS. THIS LEADS TO MORE CRITICALS FOR THE ENGINEER.

People forget about this a lot, it seems. On a successful hit, it will do about 40-50 damage (110 if it crits or something? not sure.) It is, off the top of my head, the most accurate non-sniper rifle weapon in TF2. Also, the position of your shots does not matter in the slightest- a bodyshot does just as much as a headshot. The gun can be a useful aid in destroying a sapped sentry before the engineer can get to it, as it accelerates the rate at which the sentry loses life.

• Scout - You only move at spy-speed, which is half of that of a scout's. Nobody will ever believe that (except stupid people). The only reason you might want to disguise as scout is because people may generally think, "oh hey it's a scout that's far away, he's not a spy because no idiot spy would be disguised as scout." for me, because i don't expect it, it takes a second for me to realize that a slow scout may be a spy, and if he's using the disguise for this reason, he is probably long gone. it has happened (to me) and can work.
• Soldier - There's nothing really wrong with this disguise except that it's slow. It can catch people off guard however, but.. it's slow. Heavy - Same thing. Also, you can't spin your gun. You can catch people off guard with it, though.
• Medic - Usually people expect you to be healing or have your healgun out. Also, a spy disguised as a medic does not have an ubercharge percentage displayed. Medics also move oh-so-slightly faster than spies, not that most people would notice.
• Spy - Any decent spy should be disguised 95% of the time. If you see a spy running around undisguised, you should spycheck him. When disguised as a spy, you cannot have another disguise on top of that.

You absolutely cannot be relying on your disguise to fool people. The only real thing your disguise can do is protect you from sentry fire. When you play, you should make every effort possible to never, ever be seen by the enemy, especially your target. Use your cloak to get behind them and stab them. Obviously, engineers require different tactics, but this should work for almost everyone except scouts.

If done properly, you will be their bane. There are a few ways to handle an engineer who has a sentry and maybe a couple other things around.

• If they are behind their sentry and the sentry is pointed the other way, you can backstab the engineer and immediately plant a sapper as soon as the engineer dies. This is my favored tactic. However, if there is another sentry, it will kill you as soon as you stab the engineer. Make sure you do not switch to sapper until the knife connects with the engineer, otherwise the stab will be interrupted and there is a 99% probability you will die.
• You can spam sappers on everything in sight, and continue to plant sappers as engineers whack them off. If there is more than one engineer, or if the engineer's teammates are around, you will die. This tactic works best if your teammates are already attacking the sentries, as sapped sentries do not return fire.
• As a variation of the previous technique, you can throw sappers onto everything and then gun down the sentry, switching back to sapper as necessary to keep the sentry from killing you if an engineer is knocking the sapper off.
• If you plant a sapper on a sentry, the engineer will likely move towards the sentry to take off the sapper. If they turn their back to you, even for a second... let them have it. Hahahaha.
• I think i'm forgetting something.

• Competent players. If they are causing massive problems for your team... solve them.
• Other spies. Watch your back and pull out your revolver if you can't immediately get a backstab.
• Sentries, and by extension, engineers.
• Medic/Heavy comboes. Medics are staying near their heavies, who are slow, and heavies are massive targets for backstabbing.
• Medics. Any time you can, kill a medic. They aren't hard to kill if they're standing still/moving slowly. At the right time, the death of a single medic can be enough to tip the game in your team's favor.
• Snipers, especially if they're competent. Try to avoid being seen by them.
• Demomen. They're slower than you, so you can catch up to them (eventually) and if they die, their stickies disappear.
• Anything in front of you, if you have nothing better to kill.
• Incompetent players, if you really have nothing better to kill. More points, more criticals.
• People who've noticed that you're a spy. If you're about to die, and running away isn't feasable, unload a few rounds into them in a desperate hope of killing them. Naturally, if you have more points, you have a better chance to get lovely, lovely criticals.