It's unclear how this will affect you, but if you've destroyed the horn, it may give you some advantage.
●1st Level (HP Gauge from about 100%)
・Take advantage of obstacles.
It is safer to fight while using the obstacles on both ends as a shield.
When this obstacle enters the second stage (70% HP and up), one side is pushed away by the water.
●2nd Level (HP Gauge from about 80%)
・Take advantage of obstacles.
Obstacles are useful here as well. All of these remaining obstacles will be swept away when you enter the third level (40% HP and up).
●3rd Level (HP Gauge from about 40%)
・Aim for the Abzu.
When you're killing Abzu Shoats, you'll trigger a huge excitement along the way. The Abzu's attack power is significantly increased, but perhaps its defense is reduced.
If you can fight well without defeating Abzu Shoat, I recommend concentrating on the Abzu.
・Sleep works.
Sleep works for the Abzu. If you want to eradicate the Abzu Shoat and focus on the Abzu, put them to sleep first and then defeat them.
・Blackwater Deluge
Flush the tsunami out of two huge drains (not both at the same time, but one at a time)