Most likely Tanakafication of the upgrade/merge process:
Step 1) Acquire all 8 HQ elemental staves. No Augments or Signatures.
Step 2) Acquire all 8 HQ elemental gems and all 8 elemental stones.
Step 3) Go to Full Moon Fountain for a CS.
Step 4) Talk to a Magian Moogle who will come up with some stupid reason that you have to kill a set of 300 of such and such monsters with each element.
Step 5) The moogle will tell you to go to Full Moon Fountain.
Step 6) Go to Full Moon Fountain to come to the amazing realization that the moogle failed to impart upon you the simple facts that you cannot get the next cutscene unless it's a New Moon on Lightsday.
Step 7) After waiting for the planets to align, trade all 8 staves, then all 8 gems, then all 8 stones to the BC entrance to trigger a battle against all of the avatars at once, whose stats and levels have been raised to be a challenge to level 99 players.
Step 8) Complete the fight. Upon success, you will receive a cutscene and your staff. Upon failure, you have to start again from step 1.
For your efforts you are given:
Prism Staff
DMG: 51 Delay: 356
STR+9 DEX+9 VIT+9 AGI+9 INT+9 MND+9 CHR+9
Cure Potency +10% MP Recovered While Healing +10
(Affinity: magic attack +2, magic accuracy +2, avatar perpetuation cost -3)
Lv.99 WAR/MNK/DRK/SAM