It is Ying Release manpiulation basicly.
I agree with this response the most, and will try elaborate on it a bit. (and + rep you as well)
Shikamarus shadow style ninjuitsu has to be a type of element, because now that he is using his Senseis, trench knives that absorbs its users chakra nature. So far all type of chakra weapons have only been able to absorb only one type of elemental based chakra.*wind/lightening/shadow*
I dont think the shadow style technique is a KG, I think their hidden techniques like the Akamakichi, and Yakamura(sp?) clans techniques. Could be wrong, though.