The Finned X-Wing is an advanced variation of the classic X-Wing pattern. In a standard X-Wing, a candidate appears in exactly two cells in two rows, perfectly aligned in two columns. A Finned X-Wing is an “almost X-Wing” — the pattern is disrupted by one or more extra candidate positions (the “fin”) in one of the rows. Despite this imperfection, useful eliminations are still possible. The closely related Sashimi X-Wing works similarly but with a missing corner.
Prerequisites
Before learning Finned X-Wings, you should be comfortable with:
- Candidate notation (pencil marks) — complete candidates in every cell
- X-Wing — you must understand the standard X-Wing first
- Pointing pairs — the fin interaction uses box-line logic
- Swordfish — helpful for understanding fish pattern variations
What is a Finned X-Wing?
A standard X-Wing has a candidate in exactly two cells per row, aligned in two columns:
| Col A | Col B | |
|---|---|---|
| Row 1 | X | X |
| Row 2 | X | X |
A Finned X-Wing has an extra candidate position (the fin) in one of the rows:
| Col A | Col B | Col C | |
|---|---|---|---|
| Row 1 | X | X | |
| Row 2 | X | X | F |
The cell marked F is the fin. It disrupts the perfect X-Wing pattern but still allows eliminations — as long as the fin is in the same box as one of the X-Wing corners in its row.
Why It Still Works
Consider two scenarios:
- If the fin cell contains the candidate: Then the regular X-Wing logic doesn’t apply to Row 2, but the candidate in Row 2 is in the fin’s box. Combined with the box constraint, this acts like a pointing pair within the box.
- If the fin cell doesn’t contain the candidate: Then Row 2 has the candidate in exactly two cells (Col A and Col B), and we have a normal X-Wing.
In both cases, eliminations can be made from cells that see both the fin’s box AND the opposite column. Specifically, eliminate the candidate from cells in the fin’s box that are also in the column of the non-fin X-Wing corner.
Worked Example: Finned X-Wing
Looking for the candidate 3:
| Col 2 | Col 7 | Col 8 | |
|---|---|---|---|
| Row 1 | 3 | 3 | |
| Row 6 | 3 | 3 | 3 (fin) |
Row 1 has candidate 3 in columns 2 and 7 (perfect). Row 6 has candidate 3 in columns 2, 7, and 8. Column 8 is the fin.
Check: Is the fin (R6C8) in the same box as an X-Wing corner in Row 6? R6C7 and R6C8 are both in Box 6 (rows 4-6, columns 7-9). Yes — the fin shares a box with the R6C7 corner.
Elimination: Remove 3 from any cell that is:
- In the fin’s box (Box 6), AND
- In column 2 (the opposite X-Wing column from the fin)
Wait — that intersection is empty because column 2 doesn’t pass through Box 6. Let’s reconsider: the elimination happens at the intersection of the fin’s box and the non-fin column. Actually, the correct rule is:
Eliminate 3 from cells that see both the fin AND the X-Wing corner in the opposite row on the same side as the fin. In practice:
Remove 3 from cells in Box 6 (the fin’s box) that are in column 7 (the column shared by the X-Wing corner in the fin’s row and the opposite row) — but NOT the X-Wing cells themselves.
So if R4C7 or R5C7 have 3 as a candidate, eliminate it.
What is a Sashimi X-Wing?
A Sashimi X-Wing is the complement of a Finned X-Wing. Instead of having an extra cell, one corner of the X-Wing is missing, replaced by a fin in a nearby cell:
| Col A | Col B | Col C | |
|---|---|---|---|
| Row 1 | X | X | |
| Row 2 | X | F |
Row 2 is missing the expected corner in Col B, but has a fin in Col C (same box as the expected corner). The elimination logic is identical to the Finned X-Wing — the fin constrains the candidate to the fin’s box.
Finned X-Wing vs. Standard X-Wing
| Feature | X-Wing | Finned X-Wing | Sashimi X-Wing |
|---|---|---|---|
| Positions per row | Exactly 2 | 2 in one row, 3+ in other | 2 in one row, fin replaces corner in other |
| Extra cells | None | Fin (same box as corner) | Fin (same box as missing corner) |
| Elimination scope | Entire columns | Cells in fin’s box + column | Cells in fin’s box + column |
| Difficulty | Advanced | Expert | Expert |
The Finned X-Wing always produces fewer eliminations than a standard X-Wing because the fin restricts the elimination zone to the fin’s box.
Common Mistakes to Avoid
Fin not in the same box as a corner. The fin must share a box with an X-Wing corner in the same row. If it doesn’t, the Finned X-Wing logic doesn’t apply.
Eliminating from the entire column. Unlike a standard X-Wing, a Finned X-Wing only eliminates from the intersection of the fin’s box and the relevant column — not the entire column.
Missing the Sashimi variant. If an X-Wing pattern has a missing corner, check for a fin nearby. Sashimi patterns are easy to overlook.
Confusing with a standard X-Wing. If there’s no fin (exactly two candidates per row), use the standard X-Wing technique for broader eliminations.
Multiple fins. Some patterns have two fins. This further restricts eliminations to cells seeing all fins. This is rare and very advanced.
When to Look for a Finned X-Wing
Finned X-Wings are expert-level techniques — use them after exhausting:
- All basic and intermediate techniques
- X-Wings and Swordfish
- Skyscrapers and Two-String Kites
On SudokuPulse, Finned/Sashimi X-Wings appear in Evil puzzles, averaging about 2 applications per solve.
Finned Swordfish
The fin concept extends to Swordfish patterns as well. A Finned Swordfish has a Swordfish pattern with one or more extra cells (fins) in one of the rows. The same box-intersection logic applies — eliminations are restricted to the fin’s box. Finned Swordfish patterns are rare and only appear in the hardest puzzles.
Frequently Asked Questions
How common are Finned X-Wings?
They appear in Evil difficulty puzzles on SudokuPulse, averaging about 2 per solve. They’re less common than standard X-Wings but often appear in puzzles where a “perfect” X-Wing doesn’t quite form.
Is a Finned X-Wing harder than a regular X-Wing?
Yes. The fin adds complexity because you need to verify the box alignment and the elimination zone is more restricted. Most solvers learn the standard X-Wing well before tackling finned variants.
Can a Finned X-Wing have more than one fin?
Technically yes. Multiple fins are possible but rare. Each additional fin further restricts the elimination zone to the intersection of all fins’ boxes.
What’s the difference between Finned and Sashimi?
A Finned X-Wing has all four X-Wing positions plus a fin. A Sashimi X-Wing is missing one X-Wing position, replaced by a fin in the same box. The elimination logic is identical.
Practice Finned X-Wings
Try our Evil difficulty puzzles to encounter Finned and Sashimi X-Wings.