Arctus will try to convince the Hero to light the fire for Dementia during The Cold Flame of Agnon. Additionally, he will explain how to perform the Ritual of Dementia. He is so devoted to Arden Sul that he never eats or sleeps; he wanders endlessly around the Sacellum Arden-Sul.
After completing both the "Addiction" and "The Lady of Paranoia" quests, the Hero must speak to Sheogorath. He will reveal that the real reason they are in the Shivering Isles is to stop the Greymarch by becoming the new Sheogorath. If they fail he notes, he will "swallow their soul and vomit it into the everfilling Chamberpot of the Ageless."
After fighting a sectarian battle in Cylarne and then relighting the Great Torch in the Sacellum Arden-Sul, Sheogorath appears in the pews, clapping delightedly. He says that the Greymarch is rapidly approaching.