And honestly, it took me a few months to process everything and write a complete summary of the moments that significantly changed the finale of the AP. Because the final boss of the AP wasn't who you might have thought it would have been. Which is a good thing, because Barzillai went down like a punk in under one round of combat when the party confronted him at the Apex of Bone.
No, the final boss of the AP was... Mangvhune, of all people. Mangvhune survived the initial encounter with the party... because the party ran from him once he took out the Champion of Irori in under one round. But the thing is that when the Champion of Irori fell, it was the first PC death in the entire AP. Between me being a rookie GM and my players being experienced veterans, they went all the way until the halfway point of Book Five before there was a PC death.
Because of that, I heavily edited Mangvhune's section to instill that all-important threat of a TPK into the group. Because until this point, a TPK simply wasn't a possibility that was entering the minds of my players. They didn't feel like they were in danger. Which led to Mangvhune becoming the enemy they dreaded the most as he survived far longer than he was supposed to. And that whenever he showed up, it was extremely tense and a player always died. He even managed to actually cause a near-TPK at their penultimate encounter.
He's still alive by the end of the AP, for crying out loud. Mangvhune was even addressed as the party's "actual archnemesis" after they got back from Hell and destroyed Barzillai at the Apex of Bone. This kind of happened because A) Mangvhune made everything so extremely personal. And B) he openly revealed that he had been manipulating the PCs to accomplish his own goals. But because of what was happening, the PCs knew they had to do what he wanted.
Long story short, the PCs beat the AP and thwarted Barzillai's scheme. But Mangvhune was able to use them to create an "awakened" demon army for Shax at the final confrontation located at the Soul Anchor. The PCs were able to regain control of the Soul Anchor, but Mangvhune retreated after the PCs managed to survive all the forces he could marshal against them. Since he accomplished his mission, he saw no point in throwing his life away and was actually amused that the PCs were able to give him his first real defeat in all of his existence.
