Is that only required to set the difficulty to Nightmare when it triggered with NPC or actions when running story event? Or in what condition? Or the full NG+?
#Please define "to complete the entirety of the main story on Nightmare difficulty".
subtle bramble
twin sorrel
Is that only required to set the difficulty to Nightmare when it triggered with ...
Change to Nightmare and start a new game or NG+ and play through the entire story (campaign).