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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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Theme: Antisymmetry

Author/Opus: This is the 30th puzzle from our contributing puzzlemaster JinHoo Ahn.

Rules: Standard Arrow Sudoku rules. Also, standard Thermo-Sudoku rules.

Difficulty: 2.5 stars

Time Standards (highlight to view): Grandmaster = 2:30, Master = 3:15, Expert = 6:30

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.

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Theme: Sun Rays

Author/Opus: This is the 7th puzzle from guest contributor Akash Doulani.

Rules: Standard Thermo-Sudoku rules.

Difficulty: 3.5 stars

Time Standards (highlight to view): Grandmaster = 4:45, Master = 8:30, Expert = 17:00

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

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2 and Masterpiece Sudoku Mix 2.

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Theme: Pentominoes

Author/Opus: This is the 12th puzzle from guest contributor Zoltán Horváth.

Rules: Standard Thermo-Sudoku rules.

Difficulty: 4 stars

Time Standards (highlight to view): Grandmaster = 6:45, Master = 9:30, Expert = 19:00

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

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2 and Masterpiece Sudoku Mix 2.

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Theme: Clueless

Author/Opus: This is the 366th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Standard Thermo-Sudoku rules.

Difficulty: 4 stars

Time Standards (highlight to view): Grandmaster = 6:15, Master = 10:00, Expert = 20:00

Solution: PDF; a solution video from the author is also available here and another from Cracking the Cryptic is here.

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2 and Masterpiece Sudoku Mix 2.

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

Theme: Floating 74’s

Author/Opus: This is the 69th puzzle from our contributing puzzlemaster John Bulten.

Rules: Standard Thermo-Sudoku rules.

Difficulty: 3 stars

Time Standards (highlight to view): Grandmaster = 4:00, Master = 5:00, Expert = 10:00

Solution: PDF

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2 and Masterpiece Sudoku Mix 2.

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Theme: Hot and Cold

Author/Opus: This is the 16th puzzle from guest contributor Bryce Herdt.

Rules: Standard Thermo-Sudoku rules. (Note: The coloration of the hot/cold thermometers is only for aesthetic purposes and all thermometers obey standard rules.)

Difficulty: 3.5 stars

Time Standards (highlight to view): Grandmaster = 5:30, Master = 8:00, Expert = 16:00

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

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2 and Masterpiece Sudoku Mix 2.

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

Theme: Funnel

Author/Opus: This is the 4th puzzle from guest contributor Kishore Kumar Sridharan.

Rules: Standard Thermo-Sudoku rules.

Difficulty: 2.5 stars

Time Standards (highlight to view): Grandmaster = 3:00, Master = 4:30, Expert = 9:00

Solution: PDF

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2.

Here are our best Sudoku puzzles of 2019, selected from the 31 web posts in this category:

Our first favorite puzzle was a very nicely themed Killer Sudoku by Serkan Yürekli with a rocket theme and a visual countdown in the grid.

Guest contributor Chris Green put together a paired set of Tight Fit Sudoku with a really interesting challenge that stretched the way you tend to think about this style.

Our next two top Sudoku are both clueless varieties. First, from Thomas Snyder, aka Dr. Sudoku, is this clueless Arrow Sudoku.

Ashish Kumar made a clueless Thermo-Sudoku in preparation for the World Puzzle Championship that was also one of our top puzzles.

But the overall best sudoku of 2019 goes to an unusual puzzle which was a Birthday Surprise Sudoku from Prasanna Seshadri that was a nearly perfect puzzle for his 28th birthday.

All of these best Sudoku puzzles are collected in this PDF file.

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Theme: Clueless; World Puzzle Championship (WPC)

Author/Opus: This is the 41st puzzle from our contributing puzzlemaster Ashish Kumar.

Rules: Standard Thermo-Sudoku rules.

Answer String: Enter the 4th row from left to right, followed by a comma, followed by the 8th row from left to right.

Time Standards (highlight to view): Grandmaster = 8:00, Master = 11:30, Expert = 23:00

Solution: PDF

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2.