The Jellyfish extends X-Wing and Swordfish patterns to four rows and four columns, enabling candidate eliminations across four covering lines.
A Jellyfish pattern occurs when you focus on a single candidate number and find four rows where that candidate appears in at most four cells per row, and the columns occupied by those cells collectively span exactly four columns. The candidate must be placed once in each of those four rows, and those placements will necessarily fill four of the column positions - meaning no other cell in those four columns can hold that candidate.
The Jellyfish is the natural extension of the X-Wing (2 rows, 2 columns) and Swordfish (3 rows, 3 columns). All three belong to the "fish" family, and the elimination logic is the same at every size. The defining rows restrict the candidate to the covering columns, so the candidate is eliminated from all non-defining cells in those columns.
Because the pattern spans four rows and four columns, the Jellyfish is substantially harder to spot than its smaller siblings. Each base row can have two, three, or four candidate positions, as long as the total column coverage is exactly four. This variability makes systematic searching essential. For Sudoku terminology, see our glossary.
The Jellyfish is reserved for the most challenging puzzles - those where X-Wings, Swordfish, XY-Wings, and Coloring have all been exhausted. It appears almost exclusively in expert-level puzzles and competition grids.
Because of its rarity, many advanced solvers reach for Forcing Chains before attempting to find a Jellyfish. However, knowing the technique gives you another tool when chains prove elusive. For the complete progression, visit our strategy guide or review how to play Sudoku.
The Jellyfish is classified as an expert-level technique. It demands systematic candidate analysis, strong pattern recognition, and patience - qualities that define elite Sudoku solvers.
Never needed - far beyond what easy puzzles require
Never needed - intermediate techniques are sufficient
Extremely rare - simpler advanced techniques usually work
Occasionally needed for the most challenging grids
A Jellyfish is an expert-level technique that extends the X-Wing and Swordfish patterns to four rows and four columns. When a candidate number appears in at most four positions in each of four rows, and those positions collectively span exactly four columns, the candidate can be eliminated from all other cells in those four columns.
X-Wing uses 2 rows and 2 columns. Swordfish uses 3 rows and 3 columns. Jellyfish uses 4 rows and 4 columns. They all belong to the same "fish" family of techniques - the elimination logic is identical, just applied to progressively larger patterns. As the pattern size increases, it becomes harder to spot but can produce more eliminations.
Jellyfish patterns are extremely rare. Most expert-level puzzles can be solved without them. They occasionally appear in competition-level puzzles and puzzles specifically designed to require advanced techniques. Many experienced solvers have never encountered one in practice.
Yes, like X-Wing and Swordfish, Jellyfish works symmetrically. You can define it using four columns as the base lines and four rows as the covering lines. The elimination logic is identical - just swap the role of rows and columns.
Theoretically, fish patterns can extend to five or more lines (Squirmbag, Whale, Leviathan), but these are vanishingly rare in standard 9x9 Sudoku. In practice, the maximum useful fish size is the Jellyfish (4 lines). Beyond that, other techniques like Forcing Chains are typically more practical.
Track digit 5 across the board. We're hunting for four rows that confine 5 to the same four columns.
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