A Jellyfish is the four-line fish — X-Wing (2), Swordfish (3), Jellyfish (4).
Same single-digit ownership idea, bigger net.
Before this: Learn X-Wing and Swordfish first.
Why it works
Counting: four rows must place the digit into four shared columns, one each without sharing a column. If a victim killed one fish column, four digits could not fit in three columns.
Reduction: assume a fish cell true → remaining pattern collapses toward a smaller fish you’ve already proved.
Those four columns are occupied — clear the digit elsewhere on them.
Demonstration
Pick a digit. Look for four rows confined to the same four columns.
The green cells lock 5 to this 4×4 fish. Four rows need four columns.
Counting (or reducing to a smaller fish) shows all four columns get 5. That pattern is a Jellyfish.
Eliminate 5 from the rest of those columns (red).
Example 1
For one digit, find four lines sharing the same four crossing lines.
This is a Jellyfish on 9.
Remove 9 from the rest of those lines (red). Four rows need four columns — a victim would leave too few homes.
Example 2
For one digit, find four lines sharing the same four crossing lines.
This is a Jellyfish on 4.
Remove 4 from the rest of those lines (red). Four rows need four columns — a victim would leave too few homes.