There seem to be three kinds of mirroring: What you see in a mirror, mimicry and instant object replication. The first depends on symmetry, the second depends on synchronicity and the third on identity. Andrew Carson of Dungeon7Sciences discusses what a mirror image is about and why the mirror doesn’t show us upside down as well.
In psychological or theatrical terms, mirroring (mimicry) is concurrently copying what someone else is doing (perhaps while communicating with them). Group synchronized dancing (or swimming) are good examples of this. It is called satire when the mimicry is delayed.
In Computer terms, a mirror is an exact copy of data of some extent of storage. On the Web, mirrors contain repositories of desired software or replicated data, useful when there is a surge in demand for a particular article, picture, software program or datum.
There is a description of Mirror Sudoku which requires that the Sudoku puzzle starting number placements be symmetrical horizontally and/or vertically. This puzzle with its starting number positions conforms to horizontal and vertical symmetries.
Remember to draw the numbers slowly and precisely. It’s an alternate universe you’re trying for.