Hmm... not so sure some of that is all that difficult. I can write forwards and backwards with either hand (though am faster/neater with one hand than with the other, just from one hand having a lot more practice). I imagine -- though haven't tried this myself -- that the harder task is writing two different things at once. I also haven't tried simultaneous mirror writing; never had a need to. I have seen others, most notably
Antal Dorati, do it, though; apparently, his ability to do this was well-known enough for people to ask him to mirror write when asking for his autograph. (I did not ask him for this; his autograph was enough for me.)
ETA: I can also write upside down, apparently; just tried. Printing is neater/faster than cursive, but both are reasonably legible. Surely others can do this, too, and don't know that they can unless/until they try!