Peak Sudoku
Fish, wings, chains & uniquenessPeak Score 65–80

Finned X-Wing

An X-Wing plus one or two extra candidates (the fin) inside one box.

Also known as: Finned Fish, Imperfect X-Wing

Quick Summary

A Finned X-Wing is an X-Wing with one or two extra candidate cells (the fin) in the same 3×3 box as one of its corners. Eliminations are restricted to cells that see both the fin and the standard elimination cell.

Understanding the Finned X-Wing Technique

In practical play, nearly complete X-Wings occur frequently, spoiled only by an extra candidate or two in one row. If those extra candidates (the fin) reside in the same 3×3 box as one corner of the X-Wing, we can still deduce a powerful elimination. Either the fin is false (in which case a standard X-Wing exists), or the fin is true (in which case the digit is in that box). Any cell that sees both the standard X-Wing elimination and the fin will be cleared in both scenarios.

Visual Examples

Green cells highlight the Finned X-Wing pattern, amber cells denote where candidates are affected, and struck-through pencil marks show the eliminations. Use the buttons or arrow keys to browse examples.

Example 1 of 5
Column 8 has 7 only in rows 5 and 7. Column 6 has 7 in those same rows plus a fin at R4C6. If the fin holds 7 it stays in that box; if not it's a plain X-Wing – either way 7 leaves the rest of row 5 inside that box.
Removes: 7 from R5C4

How to Spot & Solve a Finned X-Wing (Step-by-Step Guide)

The complete visual scanning and logical deduction process to execute this technique:

  • 1Look for an X-Wing pattern on a digit where one corner has one or two extra candidate cells (the fin) in the same 3×3 box.
  • 2Consider outcome 1: If the fin turns out to be false, a clean X-Wing forms and clears the intersecting column.
  • 3Consider outcome 2: If the fin turns out to be true, the digit lands in that 3×3 box and clears the rest of that box.
  • 4Identify the overlap: cells that lie in both the target column and that same 3×3 box.
  • 5Eliminate the candidate from those intersection cells, which are cleared under both outcomes.

Common Traps & Mistakes to Avoid

  • Trying to eliminate candidates along the entire column. In a finned fish, eliminations only occur within the box containing the fin.
  • The fin must be in the same 3×3 box as a corner of the fish; if it is outside, the technique does not hold.

Frequently Asked Questions

Where do eliminations occur in a Finned X-Wing?

Only in cells that see both the fin and the X-Wing corner cell in the same box and column/row.

Expand your repertoire by learning prerequisites and advanced counterparts:

X-WingPeak Score 55–70

A digit restricted to exactly two cells in two different rows, forming a rectangle.

Read guide →
SkyscraperPeak Score 60–75

Two rows (or columns) where a digit has exactly two positions, sharing one column (or row).

Read guide →

Ready to Practice Finned X-Wing?

Try a puzzle in the Tough tier (Peak Score 61–70), or browse all 25 techniques.

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