How to kill a Nightmare Nightmare

Callahan Nyx, like many in his world, was blessed with great power. However, Nyx's is a bit different from others...more specifically he is not one of the 'blessed' but one of the 'cursed'. He was 'blessed' with the power to control and dominate those around him, simply with the power of his voice... (P.S. I'm terrible at writing up a synopsis, but please at least look at this.)