Nael Deus Darnus as an enemy has been discovered in the dats. One of his attacks is a seeming short duration debuff that will cause you to explode ala Allagan Rot.
Quest Text indicates that he is the the final encounter in Turn 9.
http://xivdb.com/?quest/66849/Another-Turn-in-the-Coil
http://xivdb.com/?quest/66850/Alisaie%27s-Resolve
Urianger all but confirms that Nael was tempered by Bahamut the moment he activated the Lunar Transmitter, the Nael apparition also seems to indicate as much. Urianger also claims that The Crystal Tower is likely the original Allagan Lunar Transmitter. Alisae claims that Nael was dead already, but the text seems unclear on whether this is the case for Louisoix as well (Edit: Alphinaud seems to be convinced that he's dead, while Alisae seems to believe he can be saved) . Bahamut's aetherial resurrections seem to have all of the abilities of the originals. A confrontation with Louisoix seems to be foreshadowed, as much as Alisae would like to believe she could free Lousoix through killing Bahamut. Alphinaud shows up with some ominous words, indicating that both he and Alisae hold the key to unbinding Bahamut - but that Alisae would do better to leave well enough alone.
Wow.