Photo-Feature: Spy!

First, the superficial. The Spy is a master of disguise. A master! Completely flawless in his technique - by use of simple paper masks, placed over the face, he renders himself indistinguishable from any other member of the Enemy. Such skill! So effortless! What more can be said about his prowess in the arts of deception?

Oh! Also, his watch lets him turn invisible.

So there are certain advantages possessed by our master Spy, then. However might he be countered?

Well, firstly, he's quite frail. Frail here is relative - he still can take a magazine of SMG-rounds to the chest without falling over. But, well - he's generally up against a bit more than the SMG. (As seen so dramatically above.)

Look here, for instance: a Spy in perfect position. His enemies, presently invincible though they might be, are looking the other way. A sentry-gun and ammunition-dispenser stand lonely without their Engineer, ready to be disabled and destroyed by the Spy's handy-dandy electrosapper - except that the Spy has forgotten one key thing. His disguise. The sentry will not treat this careless slip kindly.

The most common fate for the spy!

But we have been, I think, too unkind to our spies. They explode, yes. They explode often! But they do many fine things while they live. Mostly, they stab people in the back while pretending to be their team-mates, and destroy equipment that took some time and effort to construct out of little more than spite.
Also, they float!

And become invincible! ("Professional Tip:" While one might expect that a more directly powerful class, such as the pyro or demo-man or heavy, would better benefit from the temporary invulnerability granted by an "uber-charge" (illustrated above), this spy still managed to kill me. That's why I have a picture of any of these spies, or members of other classes - they killed me.)

Ladies and gentlemen - the spy! Give him a warm hand of applause, or he'll knife you in the back. (He'll probably do that anyway, but it's worth a shot.)