Scenario spoilers ahead.
I just ran this scenario with a Mandy/Tony combo, and it ended up being a joke. I feel like I must have done something wrong, but this scenario seems to lack the teeth one usually expects from the final scenario in a campaign.
The first part of the scenario is a fairly straightforward "grab the clues, get to the end" - nothing worth writing about except that interestingly enough, you are not punished for leaving doom on locations. I would have expected it to maybe move to the agenda.
I really like the main scenario gimmick that pops up in the second agenda. I think it's really well designed, flavorful, and interesting. However, those legs are pretty darn weak when the act lets you spend 1 clue for half of their life (with two people). Add to that the fact that they can't AOO, and their fight averages around 3 or so, and they're more of a meat cushion than a challenge. Mandy and Tony were able to split the legs evenly, with Mandy gobbling up clues like a high level seeker does and Tony using his many actions and guns to fill the legs with lead. Side note - "The Spinner in Darkness" is totally meaningless here. Maybe leftover copies should transfer to Atlach-Natcha in the final act?
Atlach-Natcha itself in the final act is where things are supposed to get real, except that our investigators had a dearth of clues, so two clues plus a pistol shot is all it took to down an Ancient One. Definitely a hollow victory.
Maybe we just got really lucky with the Atlach-Natcha spins and the locations that were arranged in Act 2? Either way, lots of potential here, but definitely not what I would expect from a final scenario.