What is a Finned X-Wing?
A Finned X-Wing is one number with exactly two spots in one line and the same two spots plus one or two extra spots in a parallel line, where the extra spots, the fin, sit in the same box as one corner. Either the fin holds the number, or the X-Wing does. Cells in the fin’s box that share a line with that corner lose the number either way.
Learn the plain X-Wing first: the finned version is the same pattern with a small exception. In Marble Sudoku you look for it one marble color at a time.
Use one in 4 moves
- 1Pick. One number at a time.
- 2X-Wing. Find a line with exactly two spots and a parallel line with the same two spots plus extras.
- 3Fin. Check that all extras sit in one box with a corner.
- 4Clear. Remove the number from cells in the fin’s box that line up with that corner.
Then look for singles where you removed it.
TRY IT · GUIDED EXAMPLE
Build the Finned X-Wing
Only Green is shown in color. Faded Green marbles mark every hole where Green could still go. Find Green’s spots in the two glowing columns, spot the fin, and clear the hole that both the X-Wing and the fin rule out.
This is the real board from Marble Sudoku. The nine marble colors stand for the numbers 1 to 9.
- Lines
- Fin
- Clear
- Place
Build the Finned X-Wing
Read the example in words
Column 5 can only take Green in rows 2 and 8. Column 9 can take it in rows 2 and 8 too, plus row 3: that extra spot is the fin, and it sits in the top-right box with the corner at row 2, column 9. If the fin is not Green, the columns form an X-Wing on rows 2 and 8, and row 2, column 7 loses Green. If the fin is Green, it clears its whole box, including row 2, column 7. Either way that hole can’t be Green, and it is left with a single color: Navy. With numbers turned on, Green is 5 and Navy is 8.
YOUR TURN · PRACTICE
Spot the Finned X-Wings
Each round shows the spots for one color. Tap a spot that a Finned X-Wing rules out: in a corner’s line and inside the fin’s box. On Easy the X-Wing and its fin glow. On Hard you find them yourself.
Round color:
Why a Finned X-Wing works
There are only two cases. If the fin is not 5, it drops out, and what is left is a plain X-Wing on rows 2 and 8. Then rows 2 and 8 get their 5 in columns 5 and 9, and every other cell of those rows loses 5.
If the fin is 5, its box has its 5 and every other cell in that box loses it. A cell that is in the fin’s box and in the corner’s row loses 5 in both cases, so it can’t be 5. Cells further along the row are only cleared by the X-Wing case, so they keep 5.
How to spot Finned X-Wings faster
- Look for almost X-Wings. When you check for X-Wings, note line pairs that fail only because one line has an extra spot or two.
- Find the fin’s box. The extras must all sit in one box together with one of the X-Wing corners. Otherwise there is no fin.
- Clear inside the box only. Targets are in the fin’s box and in the same line as that corner, but not in the two X-Wing lines.
- Expect small gains. A Finned X-Wing usually removes one or two candidates. That is often enough to reveal a single.
Finned X-Wing vs. X-Wing vs. Skyscraper
| Finned X-Wing | X-Wing | Skyscraper | |
|---|---|---|---|
| Spots per line | Two, and two plus a fin | Exactly two in each | Exactly two in each |
| Shape | A rectangle with a fin at one corner | A rectangle | One end lined up, one bent |
| Removes | In the fin’s box, in the corner’s line | The rest of both lines | From cells that see both tops |
| Difficulty | Advanced | Advanced | Advanced |
Common mistakes
- Fin outside the corner’s box. Every extra spot must share a box with the same corner. A spot elsewhere breaks the pattern.
- Clearing the whole line. Without the fin the X-Wing would clear the whole line. With a fin you can only clear the cells in the fin’s box.
- Fins in both lines. One line needs exactly two spots. If both lines have extras, it is not a Finned X-Wing.
- Clearing the fin. The fin keeps the number. You clear other cells in its box.
Finned X-Wing FAQ
What is a Finned X-Wing in Sudoku?
It is an X-Wing where one of the two lines has one or two extra spots for the number, all in the same box as one corner of the X-Wing. You can remove the number from cells in that box that share a line with that corner.
What is the fin?
The fin is the extra spot or spots that stop the pattern from being a plain X-Wing. It must sit in the same box as one corner.
What is a Sashimi X-Wing?
It is a Finned X-Wing where the corner next to the fin is missing too, so that line has just the fin and the other corner. The removal works the same way.
Are there Finned Swordfish?
Yes. The same idea works with a Swordfish or a Jellyfish: if the extra spots sit in one box with a corner, the cells in that box that line up with the corner lose the number.
Does this work in Marble Sudoku?
Yes. Pick one marble color, look for two lines that almost form an X-Wing, and check whether the extra hole shares a box with a corner.
When should I look for one?
When X-Wings, kites and Skyscrapers stop finding moves. Finned fish are common in expert puzzles.
PRACTICE IN THE GAME
Find a Finned X-Wing in a real puzzle
When a hard puzzle stalls, look again at the X-Wings that almost worked. One extra hole near a corner can still break the puzzle open.
Next techniqueHidden Triples
