A compilation of all the information we have thusfar:
Ouryu Cometh
Do lots of ENMs for Cloud Evokers! Cloud Evokers are used to do the BCNM. Upon beating the Ouryu BCNM, pray that a "Monarch's Orb" drops (It's been 100% so far. There are no posts saying it hasn't dropped). If so, you are almost ready (depending on your CoP status):
Storms of Fate
Now, you need to complete the entire CoP Mission list. After beating all the missions (and finishing all the CoP cutscenes), head to Rulude Gardens for yet another cutscene (regarding Bahamut!). Then head to Site #B01 and you will get a CS upon entering. Then head to the Displacement. There's a green displacement on the very west side of E7 in B01. It leads to the island in the Northwest. C-6 where you fight him. You will fight Bahamut with up to 18 others. You are given 30 minutes to fight him. When Bahamut is dead, you will get a short CS and be given a key item called, "Whisper of the Wyrmking". Head back to RuLude Gardens for another cutscene.
Bahamut notes:
Magic
Protect 5
Shell 5
Cure 5
Silencega
Graviga
Dispelga (?)
Fire V
Firega IV
Flare II
TP Moves
There were too many to catch them all. I know of at least 6 different ones he used. Many were knock back moves.
Megaflare (AOE fire damage )
Gigaflare (AOE massive fire damage )
Sweeping Flail (AOE knockback and damage, utsusemi can block)
Touchdown (AOE damage and knockback i think, and it may be blinkable )
Trample (LoS Damage and bind i think)
Absolute Terror (AOE terror)
AOE dispel (?)
The AOE radius of most of his moves was not very large. You could be in casting range and not be hit by them.
http://img.photobucket.com/albums/v6...u/img_0108.png
http://img.photobucket.com/albums/v6...u/img_0107.png
The Wyrmking Descends
After you have obtained both the whisper and an orb, you should be able to try this BCNM. This is where hardly any information is known. Please fill in more blanks as people attempt this.