Finned Jellyfish

Level 8 · Blue Belt

Strategy:

Finned & Sashimi Fish

Requires:

Finned Swordfish Jellyfish

Learn after:

Finned Squirmbag Sashimi Jellyfish

Overview

A Finned Jellyfish is a Jellyfish pattern with a fin. Eliminations are restricted to cells seeing both the fish columns and the fin.

How It Works

Find a Jellyfish where one row has candidates outside the four columns.
These extra cells form the fin.
Eliminations occur only where cells see both the cover units and the fin.

Example

Look for Finned Jellyfish.

Sudoku grid showing the initial puzzle state for Look for Finned Jellyfish.

1

Finned Jellyfish

Check digit 4 in columns 1, 2, 6 and 7. These columns form a Jellyfish pattern in rows 2, 3, 5 and 6.

Sudoku grid illustrating step 1: Finned Jellyfish — Check digit 4 in columns 1, 2, 6 and 7. These columns form a Jellyfish pattern in rows 2, 3, 5 and 6.

2

Finned Jellyfish

r1c1 is already filled with 9.

Sudoku grid illustrating step 2: Finned Jellyfish — r1c1 is already filled with 9.

3

Finned Jellyfish

r4c1 is already filled with 8.

Sudoku grid illustrating step 3: Finned Jellyfish — r4c1 is already filled with 8.

4

Finned Jellyfish

r7c1 is already filled with 3.

Sudoku grid illustrating step 4: Finned Jellyfish — r7c1 is already filled with 3.

5

Finned Jellyfish

Digit 4 cannot go in r8c1 because r8c3 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 5: Finned Jellyfish — Digit 4 cannot go in r8c1 because r8c3 is already in this row. Remove the entry or choose a different digit.

6

Finned Jellyfish

r9c1 is already filled with 1.

Sudoku grid illustrating step 6: Finned Jellyfish — r9c1 is already filled with 1.

7

Finned Jellyfish

Digit 4 cannot go in r1c2 because r1c4 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 7: Finned Jellyfish — Digit 4 cannot go in r1c2 because r1c4 is already in this row. Remove the entry or choose a different digit.

8

Finned Jellyfish

r4c2 is already filled with 1.

Sudoku grid illustrating step 8: Finned Jellyfish — r4c2 is already filled with 1.

9

Finned Jellyfish

r7c2 is already filled with 9.

Sudoku grid illustrating step 9: Finned Jellyfish — r7c2 is already filled with 9.

10

Finned Jellyfish

Digit 4 cannot go in r8c2 because r8c3 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 10: Finned Jellyfish — Digit 4 cannot go in r8c2 because r8c3 is already in this row. Remove the entry or choose a different digit.

11

Finned Jellyfish

r9c2 is already filled with 8.

Sudoku grid illustrating step 11: Finned Jellyfish — r9c2 is already filled with 8.

12

Finned Jellyfish

r1c6 is already filled with 7.

Sudoku grid illustrating step 12: Finned Jellyfish — r1c6 is already filled with 7.

13

Finned Jellyfish

r4c6 is already filled with 9.

Sudoku grid illustrating step 13: Finned Jellyfish — r4c6 is already filled with 9.

14

Finned Jellyfish

r7c6 is already filled with 8.

Sudoku grid illustrating step 14: Finned Jellyfish — r7c6 is already filled with 8.

15

Finned Jellyfish

Digit 4 cannot go in r8c6 because r8c3 is in this row and r7c5 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 15: Finned Jellyfish — Digit 4 cannot go in r8c6 because r8c3 is in this row and r7c5 is in this box. Remove the entry or choose a different digit.

16

Finned Jellyfish

r9c6 is already filled with 2.

Sudoku grid illustrating step 16: Finned Jellyfish — r9c6 is already filled with 2.

17

Finned Jellyfish

Digit 4 cannot go in r1c7 because r1c4 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 17: Finned Jellyfish — Digit 4 cannot go in r1c7 because r1c4 is already in this row. Remove the entry or choose a different digit.

18

Finned Jellyfish

r7c7 is already filled with 1.

Sudoku grid illustrating step 18: Finned Jellyfish — r7c7 is already filled with 1.

19

Finned Jellyfish

r8c7 is already filled with 9.

Sudoku grid illustrating step 19: Finned Jellyfish — r8c7 is already filled with 9.

20

Finned Jellyfish

r9c7 is already filled with 3.

Sudoku grid illustrating step 20: Finned Jellyfish — r9c7 is already filled with 3.

21

Finned Jellyfish

One base column has extra candidates in box 6. That box is the fin, so this becomes a Finned Jellyfish.

Sudoku grid illustrating step 21: Finned Jellyfish — One base column has extra candidates in box 6. That box is the fin, so this becomes a Finned Jellyfish.

22

Finned Jellyfish

Because of the fin, only cells in box 6 that also lie in rows 2, 3, 5 and 6 can lose digit 4.

Sudoku grid illustrating step 22: Finned Jellyfish — Because of the fin, only cells in box 6 that also lie in rows 2, 3, 5 and 6 can lose digit 4.

23

Finned Jellyfish

These are the cells that see both the fish structure and the fin: r5c8 and r6c8.

Sudoku grid illustrating step 23: Finned Jellyfish — These are the cells that see both the fish structure and the fin: r5c8 and r6c8.

24

Finned Jellyfish

Remove 4 from: r5c8 and r6c8.

Sudoku grid illustrating step 24: Finned Jellyfish — Remove 4 from: r5c8 and r6c8.

25

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Finned Jellyfish are extremely rare.
Only pursue these after exhausting all simpler techniques.