Hastur's new ability is that when you're devoured or insane in Arkham, the terror level increases by 1.
During final combat, are you considered to be in Arkham? I don't see why you wouldn't. Hastur is arriving to Arkham and you're meeting to stop him. You may not be definitively in a street or location, but you should still be in town. What's your take on this?
Also, during final combat, if you're driven insane, you're devoured. Does this count twice towards his terror trigger?
This became particularly important during tonight's game because a sufficiently high terror level would have resulted in doom tokens being added to Hastur—not to mention that terror-based Epic Battle card.