Jellyfish: four base lines, four cover lines
A Jellyfish is a size-four fish: one digit in four base rows is confined to four cover columns.
Key idea
Four placements must fill the four cover columns, so the digit can be removed from those columns outside the base rows.
See the move, step by step
Follow candidate 7 across rows 1, 2, 3, and 8.
Step 1 of 4
Reduce the grid to one digit
Jellyfish patterns are global. Filter for candidate 7 before comparing row location sets.
Step 2 of 4
Verify all candidates fit four columns
The base-row 7s occupy only columns 2, 3, 6, and 7.
Step 3 of 4
Remove cover-column outsiders
R5C2, R6C6, and R7C3 lie in cover columns but outside the four base rows, so their 7s are removed.
Step 4 of 4
Apply only the justified cleanup
The Jellyfish candidates remain unresolved while the cover columns lose their outsiders.
Try it on today's puzzle
Jellyfish are rare. Search only after smaller fish fail, and verify all four base lines stay inside exactly four cover lines.
Play today