Mirror IK

The concept here is, you have IK set up on one leg and you want to mirror it. You might even have some animation keys set in that leg.

Rule #1 is …

IK solver properties rollout … Parent Space set to Start Joint

To change to Parent Space/Start Joint do this:

Turn IK Enabled OFF

Change to Start Joint

Turn IK Enabled ON

Rule #2 is …

The root object must be a dummy, or anything BUT a bone.

Select all, most importantly including the parent in the front view.

Mirror … if you included everything, this will even include any animation you have.