After working on a bunch of the later episodes of Fate/Stay Night, here I'm going back in time to episode 14, where we see Rin Tohsaka's Servant Archer - Mr. Gar Himself - take on Ilyasviel von Einzbern's Servant Berserker in an epic (losing) confrontation. Berserker's true identity is Heracles, and since he's a demi-god and all, he is INSANELY powerful. First off, most attacks don't affect him. Second off, he has twelve lives (one for each of Heracles's labors). And finally, each time he's killed, he develops an immunity to whatever he was killed with (though it is possible to kill him multiple times with a single strike...don't ask how that works). I don't see how anyone controlling this guy could have lost a Grail War, but apparently, no one else has been able to control Berserker like little Ilya. I suspect that sex may be involved. (In the F/SN universe, sex can be used to replenish a Servant's mana...I'm not making this up!)

Archer, much like Shirou, has the power to Trace; in other words, he can magically reproduce any weapon he has seen, and instantly become proficient with it. (Despite his codename, he rarely ever uses a bow.) He is unique among Servants in that he has a Reality Marble - a pocket dimension where he keeps all of the blades he has made. His best spell is Unlimited Blade Works, in which he puts his whole armory to use. In the actual series, Archer copies a whole bunch of the weapons contained within Gilgamesh's Gates of Babylon, but in this comic, he has Traced weapons from...various sources.

Archer's true identity is...well, I won't ruin that one more than I already have, lol.