A killer group is a cohesive group of cells. These groups are independent of other structures on the Sudoku board and can span multiple boxes.

Groups do not contain duplicate numbers. Depending on the level of difficulty, they contain between 2 and 5 cells.

Clicking on a cell highlights the group it is in.

For each group, the sum of its individual numbers is known. In addition, Killer Sudokus contain no or only a few specifications, depending on the situation.

Example: In a Killer group with three cells whose sum is 6, only the numbers 1, 2, and 3 are located. All other additions would not result in 6.

In addition, with a killer group it can be assumed that for the area that lies within the same box, the total sum of all the numbers already revealed, the cells that belong to the group and the other cells cannot exceed the value of all cells in the box (in the case of a 3x3 box the sum is 45). This may allow assumptions to be made about the possible value of the cells located in another box.

All other elements of Killer Sudoku correspond to those of the classic Sudoku. You can find an explanation of these terms in the game instructions for Classic Sudokus.

Killer Sudokus following the Standard Sudokus Rules solution. However, they differ in terms of their requirements and therefore also how a Killer Sudoku can be solved.

In most cases, with this variant, some of the Killer groups have to be solved first.

• Begin with extreme sums: Start with cages having the largest or smallest sums as they have the fewest possible combinations.
• Look for low-sum or high-sum cages forming a 'straight line' in the early stages, allowing cross-hatching to begin.

• Apply clock arithmetic to simplify calculations or checks for single 'innies' or 'outies' on multiple cages.

• Correlate combinations of larger cages with their complementary smaller cages to simplify deductions.