In the spirit of the Akira Kurosawa film, "Kagemusha". There the shadow warrior is a warlord's alter-ego, and is hired to rally the troops when the warlord is seriously ill. The point I wish to emphasize, though, is that when the enemy is strong, it is important to avoid head-on battles, but to take diversionary tactics. Thus, you have to be fluid, phantom-like: difficult to pinpoint, appearing and disappearing at will, wearing the enemy down. Guerillas, if you like. Forcing the enemy to fight shadows. That is the sense I use the term in, as opposed to the other sense of someone tilting at shadows or windmills. Nizhal yoddha means shadow warrior in Malayalam.
Another example is that of the shadow warriors of Linux as compared to the imperial legions of Microsoft. Unlike its normal foes, whom it can vanquish through well-established means, Microsoft has found it frustrating to deal with the phantom warriors of the GNU/Linux world. See an old column of mine as well: http://in.rediff.com/news/2001/jan/01rajeev.htm
Speaking of Kurosawa, he would have appreciated the element of surrealism about the way history is handled in India. Each protagonist interprets history in ways that are self-serving, "Rashomon"-like; and each insists that his own point of view is the only one that is authentic. None are more prone to this than the Marxists of India.