Board Thread:Questions and Answers/@comment-30281815-20161108233542/@comment-14267015-20161108234852

I think it was stated that it was a mirror image of the Earth/physical world, however due to it's nature it is much easier manipulate the environment and laws of physics in the way we see them. Plus, because the Mirror Dimension exists outside the physical world and thus can't affect each other, the Masters will typically try and take any battles they might be in there to reduce causing any damage on Earth. This also makes it useful for training in magic or imprisoning malevolent beings.