Price: GBP7.99

Shop: Pickabook

Brand: Focus Multimedia

If you think you've mastered Sudoku...... think again! Prepare to blow your mind with this unlimited collection of super-difficult Sudoku puzzles. Begin with classic 9 x 9 hard puzzles as you warm yourself up for the mind-bending Sudoku 16 x 16 or the aptly named Killer Sudoku! Do you have what it takes to become the ultimate Sudoku champion? Killer Sudoku: Are you ready to take on the challenge of Killer Sudoku? Killer puzzles are a cross between Sudoku and Kakuro. The basic Sudoku rules apply but there's a twist! You also have to make sure that all the numbers within linked boxes add up to the number clue displayed in the top left corner.