Choose one digit and list, for every row, the columns where it can still go.
Swordfish
The X-Wing scaled up to three rows and three columns.
The Swordfish is the three-line version of the X-Wing. Pick a digit and find three rows in which it can only go in two or three cells, where all of those cells fall within the same three columns. The digit has to take one cell in each of the three rows, which uses up those three columns — so it can be eliminated from every other cell in those columns.
Worked example
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How to apply it
Keep only rows where the digit has two or three possible cells.
Find three such rows whose possible cells together cover exactly three columns.
Eliminate the digit from all other cells of those three columns.
The same pattern works with rows and columns swapped.
When to use it
Swordfish patterns are rare, but they appear on expert and evil grids when X-Wings run out. Not every row needs three candidates — a row with two is fine as long as all of them fit within the three columns.
Frequently asked questions
Is there a four-line version?
Yes — the Jellyfish uses four rows and four columns. It is very rare in practice.