Two diggers, one mountain. Open a path toward each other. One mine and the tunnel collapses for both.
Left click to dig. Right click to place a flag.
You dig from the left edge and your partner digs from the right. Take turns opening one cell each. A number says how many of the eight neighbouring cells are mines, and an empty cell opens its neighbours. Flags are free and do not use your turn (on a phone, press and hold a cell to flag it). You win together when the two cleared areas join. Hit a mine and you both lose. This is practice mode against a computer partner.