Variant Sudoku 101: Exam #1
(Published on 26. December 2025, 00:19 by PhoenixAki)
My Variant Sudoku 101 series introduces common variant sudoku rules, frequently using dynamic fog to help point the solver where to look next. The target audience is those who are comfortable with classic sudoku, but new to variant sudoku. In other words, you are expected to be able to identify things like (but not limited to) pairs and triples in rows/columns/boxes and know how to take advantage of them. I welcome everyone to try this series regardless, just be warned you may have a harder time if you're new to sudoku in general.
Time for your first exam! Similar to the quizzes, this features multiple rules all at play together, this time using all 4 rules introduced so far. Some of them interact with each other in similar yet unique ways, which I tried to showcase here. Check the solution video if you need a hint on how to finish up the solve, since the last step is easy to miss. Good luck!
- Normal sudoku rules apply. Place the digits 1-9 in each row, column, and 3x3 box without repetition.
- Dynamic Fog: The grid is partially covered in grey fog. Placing correct digits will clear the fog, at minimum under that cell and sometimes in other parts of the grid. No guessing is required.
- Killer Cages: Digits in dotted-line cages must sum to the number in the top left corner of the cage.
- Kropki Pairs: Digits separated by a black dot must have one digit be double the other (a 2:1 ratio). Digits separated by a white dot must be consecutive.
- German Whispers: Adjacent digits on a green line must have a difference of at least 5.
- Renban: Digits placed on purple lines must be a non-repeating set of consecutive digits in any order.
Visual impairment friendly version: here. This version has text abbreviations specifying which clue is which rule. RB for renban, GW for German whisper.
To increase accessibility to my puzzles, I include hints in my puzzle posts (see below). I also post solution videos on my Patreon and YouTube channel. Puzzles released prior to February 2026, as well as my snackdoku and variant sudoku 101 series will continue to get public solution videos on YouTube, while others will be Patreon-exclusive.
Hint 1: All 3 of the available boxes must have some progress made in them to start the puzzle. You can get 4 digits in box 2, 3 digits in box 6, and 1 digit in box 7. Most can be worked out with careful pencilmarking, but this hint will help with box 7 a bit. Think of box 7 as effectively a long white dot chain like in quiz 1. The difference is parts of the chain are renbans where the order of the digits isn't necessarily known. Important, you can place 5 in the center of this chain.
Hint 2: Once the fog clears, continue pencilmarking things thoroughly. The black dot in column 4 is immediately resolvable, and the 14 cage in box 9 resolves all of box 9 minus 2 digits. Also, once you place a digit into R6C6, that removes an option from R7C5, which in turn gives a powerful pair of digits in row 7. Throughout that, keep up with classic sudoku.
Hint 3: The combination of 7 cage and black dot in row 1 can only unfold in 2 ways. One of them is impossible.
Hint 4: The combination of 7 cage and black dot in row 1 can only unfold in 2 ways. One of them is impossible.
Solution code: box 4's digits in normal reading order (left to right, top to bottom). 9 digits.
Comments
on 28. January 2026, 01:24 by PhoenixAki
Added links to Patreon.
on 22. January 2026, 04:33 by PhoenixAki
Added hints after learning recently how to do that in HTML. Wish I knew this a few weeks ago when I went over all my posts...oh well.
on 6. January 2026, 05:16 by PhoenixAki
Updated post as part of an effort to improve consistency of rule phrasing and post layout across all my puzzles. I also included a link to a second version of the puzzle that's more accessible to solvers with visual impairments such as colorblindness.
on 4. January 2026, 19:04 by Prezombie
Nice puzzle to break into, but the hidden singles made finishing it a chore.
on 27. December 2025, 17:01 by James Moriarty
Thank you for the puzzle.
Very clever logic in the boxes initially revealed. For an easier puzzle, some of the logic is not trivial.
on 27. December 2025, 14:22 by Ndstripes
Lovely little solve, great use of dynamic fog of war, incredibly satisfying!!
on 26. December 2025, 22:36 by Plok
Wow, great puzzle. Loved the flow guided by the dynamic fog
on 26. December 2025, 03:40 by damasosos92
This puzzle was beautiful. Perfect use of the dynamic fog and the basic concepts. 9 minutes of fun!
on 26. December 2025, 01:32 by YoooDeej
I'm ready for Exam #2!
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PhoenixAki: I was a professor for a few years and this is the first time I've ever had someone be *excited* for an exam LOL
on 26. December 2025, 01:06 by michael_787
Lol... how often did the fog lift and reveal new information? Was it twice? Clever!
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PhoenixAki: Yeah, this is an example of a puzzle where the fog is mostly there to help show where to look next and not necessarily to have it be part of the logic. I considered removing it, but if I did, the final set of clues that reveal themselves would make one of the early steps a bit trivial, so I opted to keep the fog.
on 26. December 2025, 01:04 by wuc
Very nice smooth 1*. One bump on one a hidden single kept it from very smooth. Great fun thx.
