Master Killer Sudoku — Cage Chains Across the Grid

Master Killer Sudoku is rated 7.0 to 9.9, the extreme tier, and starts with an empty grid. Plan on a long session. Your board saves after every move, so a master puzzle can span several visits. It is for solvers who finish expert killers and want the logic pushed further.

What this level asks

Cage arithmetic alone will not finish these puzzles. The hardest step is a cage chain, meaning a grouped chain, or a locked set on top of the sums, and it can take more than one. The skill that matters most is bookkeeping: the 45 rule on overlapping regions, and notes you can trust, because the later steps depend on every earlier elimination.

The 45 rule scales up here. Two rows total 90 and three total 135, so a group of cages inside a region leaves a leftover group of cells with a known sum. That group acts like a cage that was never drawn, and you enumerate its combinations like any other.

30

Possible combinations: 1

• 6789

Techniques you will meet

• Everything at expert, including cage compare and the rule of parity, used earlier and more often.
• Extreme-tier tools from the ladder: finned X-Wing, alternating inference chains and almost locked sets.

Tips for this level

• Finish every cheap deduction before starting a chain. Chains are far shorter on a fully reduced board.
• Note which cage sum or region each elimination came from. If a contradiction appears, you can trace it back.
• Take a break when stuck. A fresh look often finds a cage you had overlooked.

You are ready for this level when expert grids rarely need a guess and you can say why each elimination holds.

Next step

When master grids stop surprising you, the only way up is legendary Killer. Until then, a master grid is best treated as a long evening of patient, careful work rather than a race, and finishing one without a hint is a real result.