Guns are pretty high tier, so you could just use a high-tier character. Camouflage, illusion spells, armor, regeneration, speed, use of cover, deception - combine all that in one character, and you'll hardly get hit by any kind of modern gun. 

But i think that you don't even have to be all that powerful, just versatile enough: if he had body armor or even just a pack of smokebombs, im pretty sure Vos could fight on even ground with Mac Leod. A cast of Black & White to reduce his visibility, throw around some smoke to hide, and upon having the spell go off, simply rush in and take the kill. A viable tactic if executed well enough, and even more so with body armor.