Arrghus is the boss of the Swamp Palace, a giant eyeball surrounded by smaller eyeballs. The battle takes place in a large, water-filled arena. In the first phase, Arrghus will float around, and its smaller eyeballs will protect its main eye. Your goal is to use the Hookshot to pull off the smaller eyeballs one by one. Once a smaller eyeball is pulled off, quickly hit it with your sword to destroy it.
After all the smaller eyeballs are removed, Arrghus's main eye will be exposed. It will then start to jump and slam into the water, creating shockwaves. When its main eye is exposed, hit it with your sword. It will eventually re-summon its smaller eyeballs, and you'll need to repeat the process. Be careful of its slam attacks and the smaller eyeballs that will try to ram into you. Defeat Arrghus to rescue Oren and obtain another Lorule Sage.