Kagemane no Jutsu -- Also called the Kageshibari no Jutsu, or in English the Shadow Binding Skill (or spell or curse). This pretty much the only Jutsu that Shikamaru ever uses. But he's very good at it, no isn't he?

He's very easy to underestimate because he only uses one jutsu, and frankly he should be underestimated for it. A ninja who doesn't know very many jutsu's can't pull very surprises and everyone is looking for signs where in which he will use that one jutsu. Yet, Shikamura takes everything into account because he's used to looking for things that would cast a shadow while others are not. He is most definently an expert.

However, Shikamaru is smart and he can work little things into his advantage. Anything in the enviroment that could cast a shadow he will use.