How to play

Under the fog lies a solved sudoku: every digit appears once in each row, column and block. A few cells start open, and they never hold a mine.

Mines are scattered over the board separately, as in minesweeper. A mine can sit under any digit.

An open cell can show a small round number: how many mines are among its eight neighbours. Each block shows how many mines it holds. Some starting cells keep their count to themselves and show an empty ring.

Raise a flag on a closed cell you think hides a mine: right-click the cell, or double-tap it on a touch screen. The flag is your plan: it decides what a piece does when it passes that cell.

Your hand holds five pieces, each with a digit on its card. Put one on a closed cell and you're saying the cell holds that digit.

Right digit, no mine: the cell opens and the piece stays on it as a sensor. A rook, bishop or queen merges with the cell and its digit changes; a king or knight keeps its digit.

Wrong digit, no mine: the piece sits out for the rest of the board. The cell stays shut, and the game notes that the digit isn't there.

A mine blows up whatever the digit. You lose a life and the piece is destroyed.

After every piece you play, the hand refills from the deck.

Every piece on the board shows a number, its sensor. It updates after every action.

A white piece counts the mines left in its zone, like a minesweeper number. A black piece counts the closed cells in its zone that hide its own digit, the one on its card. A mine in the cell doesn't change that.

A king's zone is the eight cells around it, a knight's the eight cells an L-jump away. A rook, bishop or queen looks along its lines, through closed cells only: each line stops before the first open cell or piece.

A piece on the board moves by its chess rules onto a closed cell. The digit isn't checked on a board move; the mines and your flags decide. Each board move costs one stamina: a knight has three, every other piece two. Placing from the hand costs none.

A rook, bishop or queen opens every cell on its path. A mine under your flag is defused. A flag with no mine under it turns into a question mark: the piece stops there, sits out, and you lose 10 points. A mine with no flag blows up. A rook can also glide along open cells for free: it opens nothing and only lines up its sensor.

A king or knight makes one step or one jump, with no path in between, and a flag doesn't protect it. A mine under a king or knight blows up, flag or not.

Right-click a knight, or hold it on a touch screen, to raise its flag, and it jumps like a minesweeper. Onto a mine, it defuses it. Onto an empty cell, it leaves a question mark and sits out. While it keeps hitting, it keeps jumping.

Hold down on a closed cell until the fuse burns round it. That probes the cell without a piece.

On a mine, the mine is defused and the cell opens, worth 10 points. On an empty cell, the cell turns into a question mark for good and you lose 10 points. A probe isn't a move and costs no stamina.

Each king on the board has one spare life per board. If you probe an empty cell in the 3×3 around him, he spends it instead: the cell stays closed and nothing is lost.

Discard as many pieces as you like: the piece leaves your hand and a new one comes in from the deck. A discard isn't a move and scores nothing. The deck is finite, and that is the limit.

Merge: drag one piece in your hand onto another. The digits add up round the circle from 1 to the board size, and the top digit counts as 1. On a 6×6 board a 3 fed to a 3 makes 6, and a 6 fed to a 3 makes 4. The piece you fed is discarded.

Defuse every mine and the board is won. That's a Wipe. Mines that blew up count as done, and you don't have to open every cell.

You have 3 lives. Every mine that blows up takes one. Lose all three, or run out of pieces with nothing left to move, and the board is lost.

Points come from the digits you open, with more for mines defused on the same move. Your score counts them in pawns, ten points to a pawn, and goes on your result card.