The air gets crisper with Hard Fall Sudoku! This difficult sudoku puzzle level is sure to test your sudoku level to the extreme. You'll need to start using notes in this hard level, if you haven't done so already. To activate sudoku notes click the pencil. You'll notice the squares around the numbers are removed. This denotes you are in sudoku note mode. Enter the number into the space by clicking the number on the sides or using your keyboard.