Sudoku technique · First needed at: Extreme ●●●●●●●●

Finned X-Wing

An X-Wing with a spare place or two in one box: either the X-Wing holds or the number is in that box, and the cells that see both lose it.

An example from a real puzzle

How to spot it

1. Look for an X-Wing spoiled by one or two extra places — the fin — inside one box.
2. Only cells in the X-Wing's columns that also see the fin lose the number.

Why it works

Either the X-Wing holds, or the number sits in the fin. A cell that loses the number in both cases can be cleared.