Whee, lame title. But Terry's new 'archdemon' form doesn't -have- a good name yet.
It is (as you can probably tell), a hodgepodge of various RPG characters. Yes, this is on purpose; he's -supposed- to be derivative, as the form is a literal 'reflection' of actual game protagonists. Only all broken up and reassembled into one (mostly) cohesive whole.
FF/DMC/SMT:N, all influences. Probably some other stuff too.