Sudoku rules, twelve ways

Every mode in Box Brain Sudoku, in plain words. Start with Classic: the other eleven keep its rules and add one twist.

• Classic

  The original.

• Killer

  Sudoku with sums.

• Jigsaw

  Boxes become shapes.

• Thermo

  Digits that climb.

• Arrow

  Circles that add up.

• Sandwich

  What lies between 1 and 9.

• Kropki

  Dots between neighbours.

• Greater Than

  Signs between neighbours.

• Diagonal

  Two extra lines.

• Hyper

  Four extra boxes.

• Anti-Knight

  Chess meets sudoku.

• Even-Odd

  Even and odd clues.