So this part 2 did expand the world building and it really do look like the drama was making use of the Jejudo myths, but to what extent I have no idea.
Still, as much as the writing could've expanded better, the plot did progress further and we finally get to see the main villain Gungtan in action. I mean, it would've been lame if the story ended with the main bad guy not really showing his full capabilities.

From the first part we were given a big twist about Yeomji actually allying with Gungtan. And we're finally getting more details on what truly happen in the past and how it could've affected the present outcome. Not to mention we're also given a third party who seemed to have a hand in many things happening... the we never actually get that fair and this plot ended up being open ended.

To be honest, with so many new details it make me wonder if the story could be wrapped up in just six more episodes. But it did and the final episode did provide possibilities for future continuations, should there be plans for it. For a story that was based on a webtoon, I'm happy to see quite a number of pretty anime-ish and webtoon-ish scenes. So in that sense I'm very satisfied. Plus, Kim Namgil plays a half-demon demon slayer, dude... and Eunwoo finally get to have some jedi moments! Rather than dwell on stuff that the drama did not show, one might as well enjoy the pretty visuals we did get.