But why do you think it is excellent?
I think it is a highly interesting attempt to implement on the chessboard
something that happens elsewhere; but to actually play the game,
especially without computer help, is a little bit awful because of the
difficulty of keeping track of the timings of the trapdoors.
The companion game is 'Koopa Chess', also based on Mario. It was written
post-NOST and pre-HansB, so it isn't available anywhere.
A copy of the rules of Koopa Chess is included in the box which has been
packed for a year and all I need to do is carry it yo the post office and
put some darned postage on it.