It's actually more aligned with the runs in the NAN books, in which you have to try to stymie several lesser activities of a toxic shaman that are designed to build up and amplify the issues that are brought to a head in the final confrontation. What's just as important is that if s/he succeeds in any one lesser activity, the Threat Rating went up by 1; failure brought it down by 1. So succeeding at cutting his legs out from under him in each of the 3-4 precursor activities means you just have to face one nasty mage; failure to stop him means that the aforementioned one nasty mage suddenly has a much, much larger pool of power to access, and which he can feed into the big spell/ritual/whatever at the end.
Blowing up the Yellowstone supercaldera and send the world into a major ice age. Sounds Avenger toxic to me...