 So you want to make your own custom VDM brush, not a problem. In the lightbox hit miscellaneous and brush 3D template. Increase the divisions to max and from here hold control and mask the edges. Then you can use any sculpting methods you want. I am just going to use other VDMs to make my VDM. When you're done, get the camera at a perfect front view, select the chisel creature brush and under brush create and pick multi alpha brush, you're done. From here you save it exactly the same way you would any other brush. Hope that helps and as always hope you have a fantastic day and I'll see you around.