Once you have all 6 key items, proceed to Full Moon Fountain for the final battlefield and a cut scene.
Battle name: "Waking the Beast". Player limit: 18. Time limit: 30 minutes.
Buffs will NOT wear upon entry.
Once you defeat this final battlefield, random Avatar weapons may drop, and you will also receive a Faded Ruby.
The sequence for the battle is as such:
Carbuncle Prime will appear and will stay until he reaches 75% HP, at which point he'll disappear.
In its place a random avatar prime will appear. When it's dead, Carbuncle Prime will appear.
Deplete Carbuncle Prime's HP to 50%, and he'll disappear.
In its place will appear two random avatar primes that have not appeared before. When they're dead, Carbuncle Prime will reappear.
Deplete Carbuncle Prime's HP to 25%, and he'll disappear.
In its place will appear three celestial avatar primes that have not appeared previously. Defeat them and Carbuncle Prime will reappear.
This time there will be five Carbuncle Primes with 25% HP. The Carbuncles will astral flow upon the first prime defeat or their astral flow timer is up (about 1 minute). Defeat all five Carbuncles to win the battle.
After the battle choose either yes ("Disturber of Slumber" title) or no ("Interrupter of Dreams" title), if you want to give the energy back to the fountain or not.
Carbuncle wants you to visit all the protocrystals and gather the elemental energy of the sleeping gods. Will their imminent awakening mean fortune or doom for Vana'diel? Only Carbuncle's ancient friend at the Full Moon Fountain may know...
SPOILER WARNING: Click here for additional details about this story line.