Challenge Sudoku and Kakuro Challenge in one box. Sudoku is a game of placing numbers in a grid so that each number appears only once in each row or column. Challenge Sudoku offers three different ways to play: Standard, Challenge and Solitaire Sudoku. In Kakuro Challenge, 2-4 players make rows on a board, on which they try to place their numbers in a way that the sum of those numbers is the same as a predetermined number.