Here is this weekend’s special – a unique and neverseenbefore Killer Butterfly X
There are 4 “classic” 9×9 Sudoku puzzles inside this one. They all overlap and they all must be solved according to the rules of Sudoku and Killer Sudoku. You can use Twin Nonets solving technique for this one!
However, in contrast with the previous Killer Butterfly, this puzzle must have all numbers from 1 to 9 on ALL diagonals in the puzzle. There are 8 diagonals altogether – make sure you take good care of them.
Warning: This puzzle could be dangerous to your mental health. Do not attempt if not confident!
(click to download or rightclick to save the image)
I have been providing these puzzles for FREE since 2005. Please consider clicking this “Like” button Clicking it will help in keeping this website free. 

killer sudoku books 
To see the solution to this puzzle click here
Solution – first step
Have fun!
UPDATE: I had a fair number of people expressing interest and commending Butterfly puzzles, so I intend to promote them a bit more. Therefore, as of Monday January 30, expect at least 2 Butterfly (X) puzzles every week on the Daily Sudoku variants page.
4 Comments
I really enjoy the butterfly concept, and this one began as a real stumper. However, without giving away any significant details, I have to ask: is that noticeable pattern among “outer” nonets an unavoidable artifact of making a butterflyX sudoku? If so, I think it might remove some of the luster from this otherwise clever mishmash of favorite puzzle styles.
It reminded me of last year’s US Puzzle Championships, which had a “Toroidal sudoku”. As it turned out, the whole thing was essentially a repeated pattern. I don’t know if all toroidals are that way, but I’ve got a hunch…
ZD (NM, USA)
ZD, I know what you mean by the “noticeable” pattern, but I can assure you that it’s not unavoidable. I have created a few where the “twin nonets” aren’t _identical_, so you can’t rely on that fact when solving these puzzles.
I intend to further promote this beautiful concept suggested by “udosuk”, which I made even more complex by adding the “X” factor. Therefore, expect more of Butterfly X puzzles in the future! 🙂
easy, Ok, it took a while, but the X factor actually makes these particular puzzles easier.
The first few steps were a little tricky, but once they were out of the way, the rest almost filled itself in.
However, I still enjoyed it!
Argon0
The first step, for me (after the 12s and the 689) was to create some extra cages and solve some of the numbers by the addition method (1 row HAS to equal 45 – yes I know you’ve got a special name for that, but can’t remember it).
Actually there was a step before that…
As the outside Nonets contain the same numbers in each column/row (with those opposite them) you can use the 12 (bottom right) to work out which of the top right nonets numbers CAN be 1 (in this case there is only 1 that can be) thus you get another number free, and thus get another number (bottom right) free too, which leads to a 3rd “free number”.. All thanks to Dominos!