Jellyfish is an extension of X-Wing and Swordfish, by considering 4x4 grid instead of 2x2 or 3x3, respectively.
The same logic as in Swordfish, applies here. If we place any candidate from the 4x4 grid, the remaining candidates form a Swordfish, so we can eliminate all other candidates from the grid rows or columns, depending on the configuration.
In general, Jellyfish occurs very rarely and we have only found 2 such occurrences in our set of 30 000 tested boards.
This is an almost perfect Jellyfish, with the only exception of H2, which has a value. The Jellyfish is configured by rows and the eliminations occur in the corresponding columns.