What XFortress did to Tetris, Uncover It did to Breakout. It added a dimension, sort of. Just as in XFortress the blocks come in from all sides, in Uncover It the paddle circles around the blocks. Difficult to explain (though the screenshot should do a good job at it), and even more difficult to play.
When you start playing, the background is completely black. As you start clearing the level, a pale picture will form. The more blocks you clear, the more contrast the picture will gain.
Uncover It needs a 386, I suppose (even my best 286 was too slow); there are no problems with a fast PC, but it seems to behave erroneously under Windows. It runs well under DOSBox, but you might have to play another game first to get mouse support.
Uncover It was published, and maybe developed, by Mirage Software (also Mirage Media, now Mirage Interactive), one of the earliest and biggest Polish game companies. Mirage Software were very big in Amiga games at the time, but it seems that Uncover It was only released for DOS. Other Mirage game on this site are Sexversi and Rooster.
There is a British company Mirage Software, known mainly for Interactive Fiction adventures for the Oric-1. As far as I know, there is no connection between the two.
