This year, we are going to have 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 first Sunday Stumper is a challenging Sudoku variation in the style of some of the unusual rule mash-ups and difficulty seen on the Cracking the Cryptic channel.

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

Theme: Have a Cracking New Year!

Author/Opus: This is the 371st puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Standard Sudoku rules. 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 thermometer shapes are in the grid; the digits along the thermometer must be strictly increasing from the round bulb to the flat end. Some rectangular cages are in the grid marked by dashed lines; the sum or product of the digits in these cages must be either 20 or 21. Finally, some arrows are given outside the grid; the sum or product of the digits along these marked diagonals must be either 20 or 21 (digits can repeat on a diagonal).

Difficulty: 5 stars

Time Standards (highlight to view): Grandmaster = 15:00, Master = 30:00, Expert = 60:00

Solution: PDF; a solution video from Cracking the Cryptic is here.

Note: Follow this link for other variations on Sudoku.

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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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 other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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Theme: XV

Author/Opus: This is the 56th puzzle from our contributing puzzlemaster Ashish Kumar.

Rules: Standard Sudoku rules. Also, whenever the digits in two adjacent cells sum to exactly 10 or 5, an X or V is placed on the edge between cells reflecting the roman numerals for 10 or 5. All adjacent cells not marked with an X or V cannot add up to 10 or 5.

Difficulty: 3.5 stars

Time Standards (highlight to view): Grandmaster = 4:00, Master = 7:00, Expert = 14:00

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

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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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 other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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Theme: Sand Timer

Author/Opus: This is the 4th puzzle from guest contributor Akash Doulani.

Rules: Standard Sudoku rules. Additionally, if a grey circle is given between two adjacent cells, then the two numbers in those cells must be consecutive. (Note: not all grey circles are given; adjacent cells without a circle may contain either consecutive numbers or nonconsecutive numbers.)

Difficulty: 3.5 stars

Time Standards (highlight to view): Grandmaster = 4:00, Master = 5:30, Expert = 11:00

Solution: PDF

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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Theme: Big X

Author/Opus: This is the 361st puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Standard Sudoku rules. Additionally, if a grey circle is given between two adjacent cells, then the two numbers in those cells must be consecutive. (Note: not all grey circles are given; adjacent cells without a circle may contain either consecutive numbers or nonconsecutive numbers.)

Difficulty: 2.5 stars

Time Standards (highlight to view): Grandmaster = 2:20, Master = 3:30, Expert = 7:00

Solution: PDF

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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Theme: RHYTHM HEAVEN

Author/Opus: This is the 325th puzzle from our contributing puzzlemaster Grant Fikes.

Rules: Variation of Sudoku rules. Instead of the digits 1-9, use the letters in “RYTM HEAVN”

Difficulty: 3 stars

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

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.