I was wondering if anyone had come across this question in nightmare play. Loragorn's ability says, "Reduce your threat to your starting threat level. (Limit once per game)" Now does that count for each scenario played? Or is it once per the whole gamut?

In the context of this LCG, the term "game" appears to refer to a single scenario. That's why you "win the game" when you complete the final quest stage in most scenarios.

Strictly speaking, then, it would seem that you could use Aragorn's ability once per scenario. If you want an added challenge, you could consider the linked scenarios as parts of a larger "game" and limit yourself to one threat reset.

In short, once per scenario, unless you want to do otherwise.