Extreme Sudoku (evil)
The top level. These puzzles hide their key move behind chains of cells that point at each other.
Extreme Sudoku, often called evil, needs XY-Wing or simple coloring. Both follow a chain of cells where one wrong assumption forces a contradiction. All easier techniques still apply, and complete notes are mandatory.
How to use the board
- Tap a cell, then a digit. On a keyboard, use 1 to 9, Backspace to erase and the arrow keys to move.
- Turn Notes on to write small candidate digits. Press N on a keyboard.
- Hint finds a naked or hidden single and tells you which one it is.
- Your game is saved in this browser. Nothing is sent anywhere.
What Extreme means
At this level, no pair, triple or fish is enough on its own. The deciding move is a chain: an XY-Wing links three cells with two candidates each, and simple coloring follows a digit through a chain of strong links. Both can eliminate a candidate in a cell that does not share a unit with the pattern.
Advice from experience
- Do not start here. Work through Hard and Expert first.
- Always keep complete, accurate notes. One missing candidate ruins a chain.
- Look for cells with exactly two candidates. They are the building blocks of XY-Wing.
- When stuck, use the solver step by step and study the chain it finds.
A word on guessing
Never guess. These puzzles are built so that logic alone finishes them, and a wrong guess usually ends with an unreadable grid. If you cannot find the move, take a break or use the solver for just that one step.
Frequently asked questions
What is an evil Sudoku?
It is the hardest common level. Ours is called Extreme and requires chain techniques such as XY-Wing and simple coloring.
Can Extreme puzzles be solved without guessing?
Yes. Each puzzle is verified to be solvable by the logic techniques we teach.
How long does an Extreme puzzle take?
Anywhere from 20 minutes to over an hour, depending on how well you know the patterns.