This year, we started posting some extra difficult Sunday Stumpers, about once a month. These will be quite tough puzzles, but with a logical path to be found (and solution videos to help). This tenth Sunday Stumper is a challenging Killer Sudoku by Prasanna Seshadri.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Y Go Extra?

Author/Opus: This is the 220th puzzle from our contributing puzzlemaster Prasanna Seshadri.

Rules: Standard Sudoku rules. Also, the sum of the digits in each cage must equal the value given in the upper-left corner of that cage. Digits cannot repeat inside a cage.

Difficulty: 5 stars

Time Standards (highlight to view): Grandmaster = 20:00, Master = 30:00, Expert = 1:00:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Killer Sudoku and this link for classic Sudoku. More Killer Sudoku puzzles can be found in Killer Sudoku by Serkan Yürekli.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: It’s T Time

Author/Opus: This is the 215th puzzle from our contributing puzzlemaster Prasanna Seshadri.

Rules: Standard Sudoku rules. Also, the sum of the digits in each cage must equal the value given in the upper-left corner of that cage. Digits cannot repeat inside a cage.

Difficulty: 4.5 stars

Time Standards (highlight to view): Grandmaster = 11:15, Master = 19:00, Expert = 38:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Killer Sudoku and this link for classic Sudoku. More Killer Sudoku puzzles can be found in Killer Sudoku by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Square Knots

Author/Opus: This is the 2nd puzzle from guest contributor Michael Rios.

Rules: Standard Sudoku rules. Also, some arrow shapes are in the grid; the sum of the digits along the path of each arrow must equal the digit in the circled cell (digits can repeat on an arrow). Some cages are in the grid marked by dashed lines; the sum of the digits in these cages must equal the value given in the upper-left corner of that cage (digits cannot repeat inside a cage). Some dots are given between two cells; a white dot shows that the digits in those cells are consecutive and a black dot shows that the digit in one of the cells has twice the value of the other (adjacent cells without dots may or may not follow these rules). Finally, some thermometer shapes are in the grid; the digits along the thermometer must be strictly increasing from the round bulb to the flat end.

Difficulty: 4.5 stars

Time Standards (highlight to view): Grandmaster = 10:45, Master = 18:45, Expert = 37:30

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Arrow Sudoku. Follow this link for more Thermo-Sudoku puzzles. More Arrow and Thermo-Sudoku puzzles can be found in The Art of Sudoku 2. More Killer Sudoku puzzles can be found in Killer Sudoku by Serkan Yürekli.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Plus and Minuses

Author/Opus: This is the 1st puzzle from guest contributor Michael Rios.

Rules: Standard Sudoku rules. Also, each row, column and bold region must contain two negative digits. The sum of the positive and negative digits in each cage must equal the value given in the upper-left corner of that cage. Digits (ignoring sign) cannot repeat inside a cage.

See also this example:

Difficulty: 5 stars

Time Standards (highlight to view): Grandmaster = 15:30, Master = 26:00, Expert = 52:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Killer Sudoku and this link for classic Sudoku. More Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

Here is a (very hard) sample puzzle from the Killer Sudoku puzzle pack by Serkan Yürekli, which was just added to our e-store.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Time Killer

Author/Opus: This puzzle comes from our managing editor Serkan Yürekli as part of his new e-book.

Rules: Standard Sudoku rules. Also, the sum of the digits in each cage must equal the value given in the upper-left corner of that cage. Digits cannot repeat inside a cage.

Difficulty: 4.5 stars

Time Standards (highlight to view): Grandmaster = 11:00, Master = 24:00, Expert = 48:00

Solution: PDF; a solution video from Cracking the Cryptic will be available here.

Note: Follow this link for more Killer Sudoku and this link for classic Sudoku. More Killer Sudoku puzzles can be found in Killer Sudoku by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Initial Impressions

Author/Opus: This is the 331st puzzle from our contributing puzzlemaster Grant Fikes.

Rules: Standard Sudoku rules. Also, the sum of the digits in each cage must equal the value given in the upper-left corner of that cage. Digits cannot repeat inside a cage.

Difficulty: 3.5 stars

Time Standards (highlight to view): Grandmaster = 4:45, Master = 7:30, Expert = 15:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Killer Sudoku and this link for classic Sudoku. More Killer Sudoku puzzles can be found in Killer Sudoku by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Stuck Z

Author/Opus: This is the 319th puzzle from our contributing puzzlemaster Grant Fikes.

Rules: Standard Sudoku rules. Also, the sum of the digits in each cage must equal the value given in the upper-left corner of that cage. Digits cannot repeat inside a cage.

Difficulty: 3.5 stars

Time Standards (highlight to view): Grandmaster = 4:00, Master = 6:15, Expert = 12:30

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Killer Sudoku and this link for classic Sudoku. More Killer Sudoku puzzles can be found in Killer Sudoku by Serkan Yürekli.