Sudoku is a logic puzzle played on a 9×9 grid. Fill every row, every column, and every 3×3 box with the digits 1 through 9 — each digit exactly once per row, column, and box.

Tap a cell to select it, then pick a digit from the keypad or press a number key on your keyboard. Use pencil marks to jot down candidates you aren't sure of yet. Undo freely — nothing is final until the grid is complete.

You have three lives per puzzle. A wrong placement costs one life. Run out and you can watch a short video to continue, or start a brand-new puzzle from the Start Over option.

Extreme puzzles sit at the edge of what a disciplined solver can crack without guessing. Chains, colouring, and unique-rectangle logic replace the simpler techniques — and sometimes you'll need all three on the same puzzle.

If you're looking for a mental workout rather than a calming session, this is the tier for it. Finishing one of these in under an hour is a genuine achievement.