Evil Sudoku

What makes evil Sudoku so hard?

Evil is the hardest tier on the ladder — sometimes called extreme or master-level Sudoku. The rules never change: every row, column and 3×3 box still holds the digits 1 to 9 exactly once. What changes is the depth of logic you need. An evil board rarely gives up easy cells; it forces you to chain several advanced techniques together before a single number falls into place.

A common myth is that fewer starting clues means a harder puzzle. It doesn’t. Difficulty comes from the hardest technique a puzzle requires, not its clue count — and that is exactly what our evil generator dials up.

Evil, extreme, master, fiendish — same beast, different names

Every site brands its top difficulty differently. What we call evil, other apps split into “extreme” and “master”. Puzzle books and newspapers often say “fiendish” or “diabolical”, and French publishers print sudoku diabolique. None of these are different puzzle types. They are labels for the same thing: a standard 9×9 whose solution demands advanced techniques.

So if you arrived here hunting for extreme Sudoku or master Sudoku, you are in the right place. The board above plays exactly that tier. The name changes from site to site; the difficulty does not.

Evil vs expert: how much harder?

Expert puzzles are usually solvable with single-cell logic and the occasional pair. Evil puzzles are a clear step up: they routinely need fish patterns and chains, often more than one, working together. The same solver who clears an expert board in a few minutes can spend far longer on an evil one.

If evil feels too brutal right now, step down to expert Sudoku and build your toolkit there before climbing back up.

How long should an evil board take? Honestly: longer than you expect. A solver who clears expert puzzles in a few minutes can spend 30 to 60 minutes on an evil one, and taking an hour or more is completely normal while the harder techniques are still new. Speed comes from recognising patterns, and that only comes from playing.

Techniques you’ll need

To finish an evil board, expect to reach for advanced patterns. We don’t re-teach strategy here — each one links out to sudoku247wiki.com, where it’s explained step by step:

• X-Wing
• Swordfish
• XY-Wing
• naked triples
• hidden triples
• forcing chains

The evil technique ladder

Roughly in the order an evil board forces them on you:

1. Singles — your opening moves. On an evil board they dry up almost immediately.
2. Pairs and triples — the bookkeeping stage. Locking two or three candidates together starts clearing the fog.
3. Locked candidates — a candidate confined to one box-line clears it from the rest of the line. Evil boards lean on this constantly.
4. X-Wing — the first true fish pattern, and the point where evil stops being polite. Expect at least one per board.
5. Swordfish — the X-Wing’s bigger sibling, spread over three rows or columns. Rarer, and meaner.
6. XY-Wing — three linked cells pivoting on shared candidates. A signature evil move.
7. Forcing chains — the deep end. Follow a candidate’s consequences until one option collapses. When nothing else moves, this does.

One honest promise: every evil puzzle we serve has a single, unique solution. There is always one correct answer to find — it just takes patience and the right technique.

More evil challenges

Want the very top of the ladder? Try the world’s hardest Sudoku. Prefer to take an evil challenge on paper? Our sister print site has printable packs, and sudoku247wiki.com covers every technique in depth.