Stones stack up row by row on a board. It's your job to knock them off before they fill up the entire board. Slide stones around like the ever-popular Slider game to form a row of stones same as the topmost row. The matching row of stones are knocked off the board preventing the stones from filling up the board. But you have to match it before time runs out or the stones get set in place. Don't let them keep stacking up.
