The Thousand Hand School of Darkshaping is a somewhat obscure school of martial arts. It was developed in the eleventh century as an offshoot of prosthetics research, and focuses on duplicating one’s limbs both on their body and in their environment.
Much of the reason for its obscurity is its difficulty, as it requires both precise casting of Darkness to mold one’s own limbs, and then a measured release that preserves the form both during release and in transit. Another reason is it is usually found to be unnerving, partly because Lightwielding is used to move the generated limbs.
The main reason it's survived is its speed. By relying so heavily on self-lensing their constructs (a technique where Light or Darkness is filtered through the caster's body before casting, greatly speeding formation at the cost of having a fixed point of origin and, in the case of Lightwielding, considerable risk), Thousand Hand techniques are extremely fast - and by using minimal amounts of Light to move one's constructs without actually reshaping them, it stays that way, while remaining surprisingly versatile.
More advanced Thousand Hand techniques involve varying the shape, size, and to a limited degree the materials of the generated limbs, and eventually grew to include modifying one's regular limbs on a temporary or permanent basis. As body-modification disciplines go it's quite limited, but remarkably safe.