If there is a villain in Mononoke, it is the unseen Emperor, living in luxury somewhere in Asuka, drinking tea and seeing other people as simple Shogi figures.

It is the emperor that wants immortality and triggers the chain of events that get the main forest god killed & cause a lot of destruction. And in the end - he is still unaffected, while Eboshi & co have to rebuild all of their infrastructure almost from zero... :P