I think the fact that he uses Hallitation is unique since only he and Zeal use the attack.
This may just be me being anal about attack patterns, but Terra Mutant can also use this attack. Let the top half of TM drain the energy from the bottom half. After the bottom dies, the top uses Hallation and then dies.
On subject, I always thought there to be some connection between Belthasar's Nu servant and Spekkio, due to this line:
This creature sleeps beyond the flow of time.
This could mean a number of things, I know, but in a place that is beyond the flow of time, there sits a "god of war", who has incredible magic power, and has the final form of a Nu. As for the mind and memory of Belthasar, I doubt the Gurus were merely engineers and advisors - they probably dealt with magic on an everyday basis, and would be required to be wizards in their own right.
If I'm making a reasoning error, or if it's just not possible due to <insert Chronoverse temporal physics here>, I'd like to know about it.