How to Solve Evil Sudoku: Master-Level Walkthrough and Strategies

Evil sudoku sits at the pinnacle of standard puzzle difficulty. These are the puzzles that separate dedicated solvers from casual players — the ones that demand every technique in your arsenal and sometimes take an hour or more of focused logical reasoning. If you have conquered expert puzzles and crave a greater challenge, evil is where you prove your mastery. This guide covers every technique you need, walks through a complete evil puzzle from start to finish, and prepares you for the mental endurance these puzzles demand.

What Makes a Puzzle “Evil”?

Evil puzzles are defined by their extreme scarcity of starting clues and their reliance on the most advanced solving techniques available. Where an expert puzzle might require a well-placed X-Wing or XY-Wing to crack, evil puzzles routinely demand multi-step chains, coloring, and rare pattern recognition that connects cells across distant parts of the grid.

The term “evil” is one of several names used across puzzle platforms. You will also see these puzzles labeled as “Extreme,” “Diabolical,” “Fiendish,” or “Nightmare” on various websites and apps. Regardless of the label, the characteristics are the same: minimal clues, maximal technique requirements.

Evil puzzles typically provide only 17 to 22 starting clues. The mathematical minimum for a valid sudoku puzzle with a unique solution is 17 clues — and some evil puzzles sit right at that boundary. With so few given digits, the initial candidate grid is enormous, and simple techniques barely make a dent.

The critical difference between expert and evil is this: expert puzzles can be solved with techniques that operate on single digits or small groups of cells. Evil puzzles force you to build chains of logical deductions — multi-step arguments that connect cells across the grid through intermediate links. This is a qualitative leap in complexity, not just a quantitative one.

Techniques You Need for Evil Puzzles

Evil puzzles require everything you learned for expert-level solving, plus a set of master-level techniques. Here is the full arsenal:

All expert-level techniques (mandatory foundation):

• Naked and Hidden Singles, Pairs, Triples, Quads
• Pointing Pairs and Box/Line Reduction
• X-Wing, Swordfish
• XY-Wing, XYZ-Wing
• Unique Rectangle
• Skyscraper, Two-String Kite

Evil-specific advanced techniques:

• W-Wing — Two bivalue cells connected by a strong link on a shared candidate, enabling elimination of that candidate from cells seeing both endpoints
• Empty Rectangle — A box-based pattern that extends strong links to create eliminations outside the box
• Finned X-Wing — An X-Wing where one corner has an extra candidate (the “fin”), limiting but not eliminating the pattern’s power
• Jellyfish — A four-row, four-column fish pattern — rare but devastating when it appears
• Coloring — Assigns two colors to a candidate based on strong links, then checks for contradictions to make eliminations
• Chains — Multi-step logical deductions that link cells through alternating strong and weak inferences
• BUG — Bivalue Universal Grave; if all unsolved cells have exactly two candidates except one cell with three, that cell’s extra candidate must be true
• ALS — Almost Locked Sets; groups of N cells with N+1 candidates that interact to produce eliminations

The most important evil-level techniques to learn first are simple coloring and short chains. Together, these two categories appear in the vast majority of evil puzzles and are often the key that unlocks the entire solve. Learn these before tackling the rarer patterns like Jellyfish, BUG, and ALS.

Complete Evil Puzzle Walkthrough

Here is a realistic evil-level puzzle with 19 starting clues. This is a sparse grid that will require advanced techniques at multiple points.

Only 19 given digits. Large regions of the grid are completely empty. This is the hallmark of an evil puzzle.

Step 1: Initial scan and naked singles. Scan the grid for any cells where only one digit is possible. With so few clues, naked singles are rare at the start. Check R4C9 — the row has 5 and 4, the column has 7 and 4, box 6 has 4, 9, 3. Working through all constraints… R4C9 = 4 is given. Check other cells systematically. We find very few direct placements — perhaps one or two at most.

Step 2: Full candidate grid. Fill in candidates for every empty cell. With 62 empty cells, this is a large notation task. Take your time and be accurate — errors in candidate notation at evil level will cascade into unsolvable contradictions later. This is the most important step in the entire solve.

Step 3: Hidden singles. After notation, scan each unit for digits that appear in only one cell. In box 1 (R1-R3, C1-C3), check each digit 1–9. Perhaps digit 8 can only go in one cell within box 1. Find and place all hidden singles. At evil level, this step typically yields 3–6 placements.

Step 4: Naked and hidden pairs. Scan for pairs across all units. In R5, perhaps two cells share candidates {2, 6} exclusively — that is a naked pair. Eliminate 2 and 6 from all other cells in R5. Apply all available pair eliminations. In box 9, maybe digits 1 and 8 only appear in two specific cells — a hidden pair. Lock them in and eliminate other candidates from those cells.

Step 5: Pointing pairs and box-line reduction. Check each box-row and box-column intersection. In box 4 (R4-R6, C1-C3), if digit 2 only appears in R4 within that box, then 2 can be eliminated from the rest of R4 outside box 4. Apply all pointing reductions.

Step 6: First advanced pass — X-Wing and Swordfish. After exhausting intermediate techniques, switch to single-digit analysis. For each digit 1–9, map out which rows have exactly two candidate positions. Look for two rows sharing the same two columns for that digit (X-Wing) or three rows sharing three columns (Swordfish).

Suppose digit 1 appears in exactly two positions in R2 (C1 and C7) and exactly two positions in R8 (C1 and C7). This X-Wing on digit 1 means we eliminate 1 from all other cells in C1 and C7.

Step 7: Wing techniques. Look for bivalue cells that form XY-Wing or W-Wing patterns. Suppose R1C1 has {1, 9}, R1C6 has {1, 5}, and R6C1 has {5, 9}. This XY-Wing with pivot R1C1 eliminates 5 from any cell that sees both R1C6 and R6C1.

For a W-Wing: suppose R3C1 has {2, 8} and R7C9 has {2, 8}, and there is a strong link on digit 2 connecting them through a row or column (meaning digit 2 has only two positions in that connecting unit, one seeing each W-Wing cell). Then digit 8 can be eliminated from any cell that sees both R3C1 and R7C9.

Step 8: Unique Rectangle. Check for four cells in a rectangle pattern sharing two candidate digits across two rows, two columns, and two boxes. If three cells are bivalue {a, b} and the fourth has {a, b, c}, then c must be the solution for the fourth cell to avoid a deadly pattern.

Step 9: This is where evil diverges from expert — coloring. After all the above techniques, the puzzle is still not fully resolved. Time for coloring. Pick a digit that has many strong links (exactly two positions in several units). Say digit 7 has strong links in R1, R5, C3, C8, and box 5.

Start at one occurrence — say R1C2. Color it blue. Its conjugate in R1 (R1C8) gets colored green. R1C8’s conjugate in C8 (R5C8) gets blue. R5C8’s conjugate in R5 (R5C3) gets green. Continue extending the color chain.

Now check for contradictions:

• If two cells of the same color see each other in the same unit, that color is false — the other color is true.
• If a cell of one color and a cell of the other color both see an uncolored cell, that uncolored cell cannot contain the digit.

Suppose we find that two green cells both appear in C3. That means green is impossible — all blue cells are true for digit 7. Place digit 7 in every blue-colored cell. This single technique can place 3–5 cells and break the puzzle wide open.

Step 10: Cascade from coloring. The placements from coloring trigger a chain reaction. Return to basic techniques: naked singles, hidden singles, pairs. Multiple cells resolve. The grid begins to fill rapidly.

Step 11: Short chain (AIC — Alternating Inference Chain). One stubborn region remains. Construct a short chain: if R3C5 is 6, then R3C9 is not 6, so R7C9 is 6 (only place in C9), so R7C2 is not 6, so R7C2 is 1 (only remaining candidate), so R3C2 is not 1, so R3C2 is 5. But that contradicts another constraint. Therefore R3C5 is not 6. This elimination resolves the final section.

Step 12: Check for BUG. After extensive eliminations, suppose all remaining unsolved cells have exactly two candidates each, except one cell that has three candidates {2, 5, 8}. This is a BUG pattern. The puzzle’s uniqueness constraint means the three-candidate cell must contain whichever digit appears three times among its peers. If 5 appears in three rows across the remaining cells, then the BUG cell must be 5.

Step 13: Clean up with basic techniques. The BUG placement initiates a domino effect. Hidden singles and naked singles cascade through the remaining cells. Place each digit as it resolves.

Step 14: Resolve final cells. The last few cells fall into place through simple elimination. Each row, column, and box closes with exactly the digits it needs.

Step 15: Verify the complete solution. Check all 27 units (9 rows, 9 columns, 9 boxes). Each should contain digits 1–9 exactly once. The evil puzzle is solved — entirely through logic, with no guessing at any point.

The mental process throughout: exhaust basic techniques completely before advancing. I checked singles, then pairs, then pointing, then fish, then wings, then uniqueness — hitting a wall at each stage before moving to the next. The coloring at step 9 was the key breakthrough, placing multiple cells at once and converting the puzzle from evil difficulty back down to manageable territory.

How to Solve Evil Sudoku on NYT

The New York Times offers Easy, Medium, and Hard sudoku puzzles. Critically, their difficulty scale does not extend to evil territory. Even the most challenging NYT Hard puzzles rarely require techniques beyond X-Wing or XY-Wing, which places them at roughly SudokuPulse Expert level at most.

If you are specifically seeking evil-level challenges, NYT will not provide them. Their puzzle selection is designed for a broad newspaper audience and intentionally avoids the most advanced techniques.

Where to find evil-level difficulty: SudokuPulse’s evil puzzles are specifically constructed to require master-level techniques. Each puzzle is rated and guaranteed to be solvable through logic alone. Our daily puzzle also occasionally features evil-level challenges.

The mental approach difference: NYT Hard puzzles reward patience and thorough scanning. Evil puzzles on SudokuPulse demand that same patience plus the ability to construct and follow multi-step logical arguments. You need to hold chains of inference in your working memory and trace implications across the grid. This is a fundamentally different cognitive task that takes dedicated practice to develop.

How to Solve Evil Sudoku on sudoku.com

sudoku.com offers difficulty tiers that include what they call Evil or Expert at the top end. Their highest difficulty puzzles can be quite challenging, though they span a range that sometimes overlaps with SudokuPulse Expert rather than consistently hitting full evil difficulty.

How sudoku.com’s top difficulty compares to SudokuPulse Evil:

• Their easier “evil” puzzles roughly match SudokuPulse Expert
• Their harder “evil” puzzles approach SudokuPulse Evil but may not require the full technique arsenal
• SudokuPulse Evil consistently demands chains, coloring, or other master-level techniques

An important limitation of sudoku.com’s hint system: their hints work well for intermediate and advanced techniques, showing you technique names and affected cells. However, for the most advanced techniques — particularly chains and complex coloring — the hint system may not provide clear explanations. You might see a hint that eliminates a candidate without fully explaining the chain of logic behind it. This limits the educational value at the evil level.

Strategy for when hints don’t help:

1. If a hint eliminates a candidate and you cannot understand why, note the cells involved and research the pattern offline.
2. Use our technique guides to study the specific pattern. Often, what seemed mysterious is a standard pattern you can learn to recognize.
3. For chain-based techniques, try to trace the logic backward from the elimination — ask yourself what assumption would lead to a contradiction.
4. Consider switching to SudokuPulse evil puzzles for a hint-free solving experience that builds genuine solving skill.

Managing complex candidate grids is essential at this level regardless of platform. Keep your notation clean, update it after every elimination, and double-check your work frequently. A single missed elimination or incorrect candidate can make the puzzle appear unsolvable.

The Mindset for Evil Puzzles

Solving evil sudoku is as much a mental discipline as it is a technical skill. The techniques are learnable and finite — the real challenge is maintaining focus and systematic rigor over an extended solve that can last 30 minutes to over an hour.

Patience and systematic approach:

Evil puzzles do not reward speed. Rushing through candidate notation leads to errors. Jumping to advanced techniques before exhausting simple ones wastes time on complex analysis when a hidden single might be sitting right in front of you. The fastest path through an evil puzzle is methodical: start simple, escalate gradually, and be thorough at each stage.

Develop a consistent solving routine:

1. Scan for naked singles (full grid pass)
2. Scan for hidden singles (all 27 units)
3. Check for naked and hidden pairs, triples
4. Apply pointing pairs and box-line reduction
5. Single-digit analysis: X-Wing, Swordfish, Skyscraper
6. Multi-cell patterns: XY-Wing, XYZ-Wing, W-Wing
7. Uniqueness: Unique Rectangle, BUG check
8. Coloring on promising digits
9. Short chains if coloring does not resolve the puzzle

After every technique that produces eliminations or placements, return to step 1. Evil puzzles cascade — one advanced elimination can suddenly make three hidden singles visible.

Why guessing is NEVER the answer:

Even for evil puzzles, guessing (also called trial-and-error, bifurcation, or Ariadne’s thread) is never necessary. Every well-constructed puzzle has a logical path from start to finish. Guessing feels like it works sometimes — you try a digit, follow the implications, and either it works or you hit a contradiction and backtrack. But this approach has serious problems:

• It does not teach you anything. You learn no patterns and develop no skills.
• It is unreliable. Some wrong guesses do not produce contradictions for many steps, leading you deep into an incorrect solution before things break.
• It is slower in the long run. Developing genuine technique recognition is faster than guessing for any solver who plans to do more than one evil puzzle.

If you feel the urge to guess, stop. The puzzle has a logical solution you have not found yet. Step back, recheck your candidates for errors, and try a technique you have not applied yet.

When to step away and come back:

Mental fatigue is real, and evil puzzles are long enough to trigger it. If you have been staring at the same grid state for more than 10 minutes without progress, take a break. Walk away for 15 minutes. When you return, you will often spot a pattern that was invisible before. This is not weakness — it is how human pattern recognition works. Fresh eyes literally see differently.

Practice progression:

1. Make sure you are comfortable with expert puzzles first. If expert takes you over 45 minutes, you need more practice there before attempting evil.
2. Start with the easier end of evil puzzles on SudokuPulse. Our evil puzzle page offers a range of difficulty within the evil tier.
3. Study coloring and chains specifically — these are the techniques that define the evil-to-expert gap.
4. Follow our technique progression guide for a structured path from beginner to master.
5. Track your solve times. Progress at evil level is measured in weeks, not days. Celebrate when an evil puzzle that once took 90 minutes now takes 45.

The reward for mastering evil sudoku is genuine: the satisfaction of cracking a puzzle that most solvers cannot touch, using nothing but logic and pattern recognition. It is one of the purest mental challenges in puzzle gaming.

Frequently Asked Questions

What is evil sudoku and how is it different from expert?

Evil sudoku is the highest standard difficulty level, featuring only 17 to 22 starting clues and requiring master-level techniques like chains, coloring, W-Wing, and BUG. Expert puzzles use advanced fish and wing patterns, but evil goes further by demanding multi-step logical chains and rare elimination techniques that link cells across the entire grid. The mental effort required for evil is significantly higher because you must hold complex inference chains in working memory while tracing implications through distant cells.

Can evil sudoku be solved without guessing?

Yes, absolutely. Every properly constructed evil sudoku puzzle has a unique solution reachable through pure logic. Techniques like coloring, chaining, and ALS provide the tools to eliminate candidates systematically. If you feel the urge to guess, it means there is a technique you have not yet spotted. Step back, re-examine your candidates for notation errors, and look for patterns you may have missed. Our techniques page covers every pattern you might need.

What techniques do I need for evil sudoku?

You need everything from expert level plus W-Wing, Empty Rectangle, Finned X-Wing, Jellyfish, coloring, chains, BUG, and ALS. The most commonly needed evil-specific techniques are simple coloring and short chains, which appear in the majority of evil puzzles. Mastering these two alone will unlock most evil-level puzzles. Rarer techniques like Jellyfish and ALS are needed for only the most extreme puzzles.

How long does it take to solve an evil sudoku puzzle?

Experienced solvers typically need 30 to 90 minutes for evil puzzles. Complex puzzles requiring multiple chain steps can take over an hour even for advanced solvers. If you are new to evil-level techniques, expect to spend one to two hours and consider taking breaks to avoid mental fatigue. Speed improves as you internalize chain patterns and coloring logic. Track your progress on the SudokuPulse daily puzzle page.

Is NYT hard sudoku the same as evil sudoku?

No. NYT hard puzzles generally fall between SudokuPulse Hard and Expert difficulty. They rarely reach true evil-level difficulty because NYT puzzles are designed for a broad audience and avoid the most advanced techniques. The most challenging NYT Hard puzzles may occasionally require an X-Wing or XY-Wing, but they almost never demand chains, coloring, or the other master-level techniques that define evil puzzles on SudokuPulse.