e.g. align the roll of bones to the source armature A script that rename the bone of unity name to/from the mixamo name. I created this script for the Mixamo add-on for Blender. The procedures is ...
3D engines have support for bone physics, this can be used for a wide variety of things: Hair that reacts to motion, gravity, and wind. Antennas, wings, tails, etc. Breast / butt / muscle jiggle.