You have to catch the new Legendaries in all 4 of the gates areas. Remora, Cameroceras, Ancient Carp, Tusoteuthis Longa
Remora: Who Gates J-11, Minnow. Snapped the line A LOT
Ancient Carp: Moh Gates K-6/K-7. Insect Paste
Tusoteuthis Longa: Dho Gates F-12/G-12, Minnow
Cameroceras: Sih Gates, map 2, H-9, Minnow. Snapped the line a couple times
Once you have successfully caught all of these POST JUNE UPDATE (so game can register them under your caught fish log) Lord of Ulbuka changes.
His HP is lower, his regen (like AV) gets crippled, he calms the fuck down... Altogether about as hard as matsya.
Also doesnt snap the line that much.