Mirroring and bridging are terms used to describe strategy to unify yourself with your opponent.
Prior to the physical point of contact if you follow your opponent's movements in a mirror image it helps you to recognize your opponent's posture and usually leads to an opportunity to make physical contact while in the meantime you syncronise with their movements setting up the potential to take control.
Once you have a sense of your opponent's posture and limits etc. bridging is the process of closing the gap in order to make physical contact, at which point the objective is to control your opponent. There is a little bit on the subject in the System guide pg 21.
Shadow boxing is a form of mirroring but solo. It's very good for checking your own posture and structure. I've got a favorite park I go to to train at sun rise and use the first shadows against a wall to train postures. It gets a bit obsessive (
) but with the lines in the brick work you can get a very good idea of your vertical and horizontal structure, limits of movement etc. I've found it is very good for checking yoga asanas as well.
Train well and best of the Season and regards to everyone on the Forum.
Chris