I've had my eye on this adventure for over a year, ever since Idle Cartulary reviewed it in September 2023. While obviously inspired by Princess Mononoke (namechecked on the first page of the adventure), the adventure is much more than just that story translated into an RPG. Perhaps the best intervention it makes is trapping the locals in between the colonizing Conquistadors and the enraged mass of boars. Unlike the citizens of Iron Town, who are actively participating in the destruction of the forest in Princess Mononoke, the people of Barangay Tindigan are faced with a fundamental lifestyle change due to the arrival of colonizers. They're not the ones who shot the Ancient Boar, but it's their village and not the Conquistadors' stone fort that will get trampled in retaliation. This change makes for a very different dilemma at play: how can you protect the innocent townsfolk without also protecting the Conquistadors who are clearly at fault for everything that happened?
This is a question with no easy answer, if your group is even interested in answering that specific question (maybe they'll work for the Conquistadors; they are offering 1000 gp as a reward after all). Still, whatever they want to do they had better act fast because as the Ancient Boar lays dying, its death throes are causing literal earthquakes. The mechanic that underlies this clock is pretty ingenious actually: an earthquake triggers every time you roll doubles on the 2d6 Wilderness Encounters table, and the Ancient Boar dies after the fifth earthquake. This means there's a 1-in-6 chance of an earthquake, so you're looking at an average of 30 wilderness encounters before everything comes down around your players' ears. That's theoretically more than enough time to explore the 20 hexes on the given hexmaps if they're really booking it through the forest.
The Wilderness Encounters is perhaps a little lacking, and for me the least inspiring part of the adventure. I particularly like the giant hermit crab using an overturned boat as its shell, but many of the other encounters don't feel like they add all that much context to the world. In particular, I would love to have some interesting people to happen upon in the forest, because the people in the keyed hexes are by and large pretty compelling.
All in all, the adventure is deceptively simple and really gives players the space they need to mull over how to resolve the presented dilemma. There are no easy answers presented in the text (because god knows that killing the Ancient Boar isn't going to be easy even though it's technically the most obvious 'solution') and that's just the way I like it. Newer GMs might find that aspect of the game a bit frustrating or confusing on first glance, but if you just venture into the Rumbling Forest I think that an answer will present itself to you one way or another if you just let it happen.