Finned Squirmbag

A Finned Squirmbag is a Squirmbag (5-fish) pattern with extra candidates forming a fin. This is one of the rarest patterns in Sudoku solving.

Technique

1. Find a Squirmbag where one row has candidates outside the five columns.
2. These extra cells are the fin.
3. Eliminations occur only in cells seeing both the cover columns and the fin.

Tips

• Finned Squirmbags are almost never needed in human-solvable puzzles.
• This is primarily of theoretical interest.