Deoxurous is the superboss of GC III and is optional. He is very though. And has 2 forms.
Created by the God, Omega, Deoxurus has extreme power and wasn't touched for 49,598 years. Ganondorf repowered it.
1st Form: HP: 59,567, Oversoul HP: 99,999 ATK: 80,000,000 MP: 999,999
Just attack the legs, then the arms. He will rebuild himself. So do this about three times. Watch out for Nexus and Ultima.
2nd Form (Arm and Legs): HP: 999,999,999 Oversoul HP: 999,999,999,999,999,999 ATK: 500,000,005 MP: 999,999,999.
Possibly the hardest boss in the first triology Deoxurous takes on his almighy form. The arm and each leg having 999,999,999 HP he is tough to destroy. Once you do destroy his arms and legs go inside him using the Clawshot. You will stumble across many Machina some weak some strong. Then you will fight the Claret Dragon once you beat him you will climb the ladder to the head and fight Ganondorf and then immediately fight the central (a.k.a Head)
Claret Dragon: HP: 899,657 Oversoul HP: 19,997,349 ATK 777,777 MP: 99,999
Ganondorf (Second Battle): HP: 99,909 Oversoul HP: 99,999 ATK: 99,999 MP: 99,999
2nd Form: Head: 1,999,999,999,999 HP (cannot be ovrsouled) ATK: 999,999,999,999,999 MP: Infinite