Thanks AmigaLive! A for the "Mirror" option - it is only called like this but it does actually what you describe already :) :D. It randomly applies one of 7 matrix transformation on the mine setup from Player 1.
As for the Versus settings, actually 2 bits in the save memory block will be sufficient for me to store both controls setup as well as "Mirror" selection. Detecting mouse/joystick on Amiga may not be possible to what I have been reading so far. Nevertheless, all good as those 2 bits will be sufficient to store the "Versus" settings for controls and "mirror".
As per the logic for Detonator game - it randomly reveals one OR NONE of the tiles around the clicked one. The same applies to tiles in 1 tile distance from the clicked one. The prabablity that none of the tiles will be revealed increases with number of tiles already uncovered.