Level one: The whole body should be experienced as having uniform density.
Level two: The body and the surrounding environment should be experienced as having uniform density.
Of course this is training for what we often refer to as "mind," but in this context it is somewhat absurd to call it mind since it is equally an experience of "body."
I had already done this practice, I just hadn't tried to put it together with my fighting skills. The basic invocation of the deity Ziwei used in Orthodox Daoist ritual and jindan (internal alchemy) includes the description, "His skin is onyx-black like the night sky."