Prepare for non stop critical hits, speed boost's, awsome special atacks that parylize, bleed, and do major damage.
-and if your human like me, you can go invisible ;D
thiefs are great because you can carry a shield which improves phisical defence greatly, kill multiple enemies after few bats of a eye with "wind breaking" and you dont have to increase your atack with your rate of critical hits. Dont forget about your evasion :3 half of the atacks will miss.
just watch out for your mana and magical defence :U eventually you will get an atack that steals mana though :3 not sure how affective that is though.