It's not that complex. The jutsu materializes the Shadow. In the past, the materialized shadow has been abused to be a myriad of things, ranging from essentially turning a forest into a living death trap of shadows. I limit the jutsu by stating that A) the only shadow that can be turned into Shadow Tendrils is that of the user and what thy extend to B) that all shadow tendrils in corporeal form can be hurt C) that the tendrils are limited as you said, but also cannot move from their origin point once summoned. They must retreat, then reposition if need be.