Before the final boss fight, travel to a scenic location on the Great Plains of Pangea and kill Derrodocus to drop Oli Grass. Equip gear that increases drop rate for luck. If you're lucky, you'll drop 4 or 5 at a time, repeatedly use the scenic spot to teleport.
After that, I continued to change the elixir of strength to Hummel. I just need to increase the attack to around 2500. Then Brother Gun equipped the Marine Halberd Berserker Mask and released the skill. He is very powerful. .I recommend using the Sin Attack Judgment rapid cannon. With "Fire Burning" skills, if you don't have mana, you can get a lot of SP after casting and hitting the attack. automatically restores SP. It's basically an infinite skill.