Evil printable sudoku

What "evil" means, precisely

This is the fifth setting. The game on this site calls it Master; the printable world calls it evil, and the search results agree with the printable world. Same grader, same filter, one rename.

Precisely: every board here could not be finished by any of the sixteen techniques the engine implements. Not "needed a hard one" — defeated the whole ladder. Across 600 boards at this setting, that was true 600 times out of 600. Average clue count, 24.6.

That makes this a different category from expert, not the next step above it. Expert boards need a chain the grader can find. These need one it cannot.

How you are supposed to finish these

Three honest answers, in order of how often they actually work:

1. A long forcing chain, built by hand. Pick the cell with the fewest candidates, assume one value, and follow the consequences until something breaks. If it breaks, the other value was right. The forcing chain article walks through the whole argument, including why it is sound despite feeling like guessing.
2. A technique outside the sixteen. There are named patterns — exotic fish, nets, almost-locked sets — that this engine does not implement because their supply is too thin to justify the code. Boards that need one are, by construction, boards the grader cannot finish.
3. Guessing and checking. Perfectly legitimate on paper. You are not being graded.

If an answer above feels unsatisfying, that is the correct reaction. This setting exists because people ask for it, not because it teaches anything the expert setting does not.

Why the sheet is still worth printing

Because the work is honest. Each board is verified unique and verified hard; there is no board here that a scanner could crack in five minutes. If what you want from a sudoku is a genuine thirty-minute fight — on a train, with a pencil, with no hints available — this is the sheet, and there is no shortage of them.

What you should not expect is a lesson. Nothing here will teach you a new pattern, because the patterns that would help are not in the ladder. If you are still building your technique set, the expert sheet is hard enough to be interesting and has an answer at the end.

Printing notes

Candidate marks on, and print two copies. You will almost certainly reach a point where you want to abandon one branch and try another; a second copy costs you nothing and saves you from erasing.

One puzzle per page, and pick the largest layout. Twenty-four clues means a lot of empty cells, which means a lot of candidate lists, which means you need the marks to be legible rather than faint. Four-per-page puts the pencil marks at roughly 5 pt, which is below the size most people can compare at a glance.

Expect to take an hour on some of these, and to put one down and come back. That is not failure — it is the setting working as intended.