Normal sudoku rules apply. Digits along an arrow sum to the value in its circle. There are 9 Vampire cells contained within the grid which are a set of the digits from 1-to-9. Each row, column and box contains exactly one Vampire cell. 9 Prey cells in the grid follow the same rules as the Vampire cells. A cell may have only one of these roles. For Arrows/Circles: Prey cells contribute no value; Vampire cells contribute the sum of the digits in the Vampire cell and the Prey cell within the same box.