Scarlet, or Amarant, has an HP of 8985. This battle could be a little difficult if you aren’t well prepared.
You need a stock of Hi-potions when fighting that boss since there will be nobody else to heal you when you get hit. At this point, ordinary potions won’t be useful.
Equip running shoes
If you have running shoes then equipping them will give you auto haste. In such a case, your turn will come more often and so winning this fight will be much easier.
Brigandine is a kind of body Armour that could provide you with good physical defense. Since all of Scarlet Hair’s attacks are physical, equipping that Armour can help you a lot.
Equip the power belt
Equip the power belt if you still have it to enable the MP attack ability. This ability can help you do a lot of physical damage easily.
Avoid hitting him when he is in the background
When he goes in the background don’t attack him for he will counter back with a physical attack that is much stronger than his normal attacks. (See How to defeat Ralvurahva in Final Fantasy 9?)
Attack him near the third pillar
If you attacked Scarlet Hair while he is behind the third pillar from the left then not only will your attack cause a lot more damage, but he also won’t counter.
Enable the man-eater ability
The man-eater ability can also help you cause more physical damage when you attack him. Make sure it is enabled.
Items to steal
This boss has both Poison Knuckles and an Ether. You can only try to steal the first since it’s a bit expensive. (See How To Win Final Fantasy 9 Card Game)
How to defeat Scarlet Hair in Final Fantasy 9?
How to Beat Scarlet Hair in FF9? Final Fantasy 9 Walkthrough: Defeating Scarlet Hair (boss)