Designing a Sudoku a Grandmaster Wouldn't Be Bored By

Most sudoku apps solve the “we need more content” problem the same way: turn a difficulty slider further to the right. More candidates to track, fewer starting numbers, longer solve times. It works, technically. It’s also not that interesting after the twentieth grid.

We wanted Grandmaster Sudoku to have a ceiling that isn’t just “harder Classic.” So instead of one difficulty axis, the Grandmaster tier changes what a cell even means:

• Diagonal X adds a constraint, not a difficulty — both main diagonals need every digit too.
• Jigsaw keeps the numbers exactly as friendly as Classic, but replaces the 3×3 boxes with irregular regions, so your box-scanning instincts stop working.
• Killer removes almost all the starting numbers and replaces them with cage sums, turning sudoku into a light arithmetic puzzle.
• Blindfold doesn’t touch the rules at all — it just makes your placed digits fade from view, so the challenge becomes memory rather than logic.
• Time-Attack puts a clock on top of Classic, where correct entries buy you time back and mistakes don’t.

None of these needed a harder generator — they needed a different rule. That turned out to be the more interesting (and more replayable) design space than just cranking up grid difficulty, and it’s the reason Grandmaster has six tiles instead of one “Expert+” button.