Finned Jellyfish

Level 11 · Red Belt

Strategy:

Finned & Sashimi Fish

Requires:

Finned Swordfish Jellyfish

Learn after:

Finned Squirmbag

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

Starting position

Look for Finned Jellyfish.

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

1

Rows 1, 3, 4 and 8 form a Jellyfish on 6

Base rows 1, 3, 4 and 8 form a Jellyfish for digit 6 in cover columns 2, 3, 7 and 8.

Sudoku grid illustrating step 1: Rows 1, 3, 4 and 8 form a Jellyfish on 6 — Base rows 1, 3, 4 and 8 form a Jellyfish for digit 6 in cover columns 2, 3, 7 and 8.

2

r1c1 is already filled

r1c1 is already filled with 3.

Sudoku grid illustrating step 2: r1c1 is already filled — r1c1 is already filled with 3.

3

6 is blocked from r1c4 by column and box

Digit 6 cannot go in r1c4 because r7c4 is in this column and r2c6 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 3: 6 is blocked from r1c4 by column and box — Digit 6 cannot go in r1c4 because r7c4 is in this column and r2c6 is in this box. Remove the entry or choose a different digit.

4

6 is blocked from r1c5 by column and box

Digit 6 cannot go in r1c5 because r5c5 is in this column and r2c6 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 4: 6 is blocked from r1c5 by column and box — Digit 6 cannot go in r1c5 because r5c5 is in this column and r2c6 is in this box. Remove the entry or choose a different digit.

5

r1c6 is already filled

r1c6 is already filled with 8.

Sudoku grid illustrating step 5: r1c6 is already filled — r1c6 is already filled with 8.

6

6 is blocked from r1c9 by the column

Digit 6 cannot go in r1c9 because r9c9 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 6: 6 is blocked from r1c9 by the column — Digit 6 cannot go in r1c9 because r9c9 is already in this column. Remove the entry or choose a different digit.

7

r3c1 is already filled

r3c1 is already filled with 2.

Sudoku grid illustrating step 7: r3c1 is already filled — r3c1 is already filled with 2.

8

r3c4 is already filled

r3c4 is already filled with 4.

Sudoku grid illustrating step 8: r3c4 is already filled — r3c4 is already filled with 4.

9

r3c5 is already filled

r3c5 is already filled with 7.

Sudoku grid illustrating step 9: r3c5 is already filled — r3c5 is already filled with 7.

10

r3c6 is already filled

r3c6 is already filled with 9.

Sudoku grid illustrating step 10: r3c6 is already filled — r3c6 is already filled with 9.

11

6 is blocked from r3c9 by the column

Digit 6 cannot go in r3c9 because r9c9 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 11: 6 is blocked from r3c9 by the column — Digit 6 cannot go in r3c9 because r9c9 is already in this column. Remove the entry or choose a different digit.

12

6 is blocked from r4c4 by column and box

Digit 6 cannot go in r4c4 because r7c4 is in this column and r5c5 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 12: 6 is blocked from r4c4 by column and box — Digit 6 cannot go in r4c4 because r7c4 is in this column and r5c5 is in this box. Remove the entry or choose a different digit.

13

r4c5 is already filled

r4c5 is already filled with 3.

Sudoku grid illustrating step 13: r4c5 is already filled — r4c5 is already filled with 3.

14

r4c6 is already filled

r4c6 is already filled with 1.

Sudoku grid illustrating step 14: r4c6 is already filled — r4c6 is already filled with 1.

15

6 is blocked from r4c9 by the column

Digit 6 cannot go in r4c9 because r9c9 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 15: 6 is blocked from r4c9 by the column — Digit 6 cannot go in r4c9 because r9c9 is already in this column. Remove the entry or choose a different digit.

16

r8c1 is already filled

r8c1 is already filled with 1.

Sudoku grid illustrating step 16: r8c1 is already filled — r8c1 is already filled with 1.

17

r8c4 is already filled

r8c4 is already filled with 8.

Sudoku grid illustrating step 17: r8c4 is already filled — r8c4 is already filled with 8.

18

r8c5 is already filled

r8c5 is already filled with 4.

Sudoku grid illustrating step 18: r8c5 is already filled — r8c5 is already filled with 4.

19

6 is blocked from r8c6 by column and box

Digit 6 cannot go in r8c6 because r2c6 is in this column and r7c4 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 19: 6 is blocked from r8c6 by column and box — Digit 6 cannot go in r8c6 because r2c6 is in this column and r7c4 is in this box. Remove the entry or choose a different digit.

20

6 is blocked from r8c9 by the column

Digit 6 cannot go in r8c9 because r9c9 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 20: 6 is blocked from r8c9 by the column — Digit 6 cannot go in r8c9 because r9c9 is already in this column. Remove the entry or choose a different digit.

21

The fin sits in box 4

One base row has extra candidates in box 4. That box is the fin, making this a Finned Jellyfish.

Sudoku grid illustrating step 21: The fin sits in box 4 — One base row has extra candidates in box 4. That box is the fin, making this a Finned Jellyfish.

22

Only box 4 can lose 6

Because of the fin, only cells in box 4 that also lie in columns 2, 3, 7 and 8 can lose digit 6.

Sudoku grid illustrating step 22: Only box 4 can lose 6 — Because of the fin, only cells in box 4 that also lie in columns 2, 3, 7 and 8 can lose digit 6.

23

Cells that see both fish and fin

These cells see both the fish structure and the fin, so they are removal targets: r6c3.

Sudoku grid illustrating step 23: Cells that see both fish and fin — These cells see both the fish structure and the fin, so they are removal targets: r6c3.

24

Remove 6 from the fin-affected cells

Remove 6 from these fin-affected cells: r6c3.

Sudoku grid illustrating step 24: Remove 6 from the fin-affected cells — Remove 6 from these fin-affected cells: r6c3.

25

Result

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.