I like the lava ring. Ideally, and this would be way out there for us, the action would be taking place within that circle. But even so, it’s a striking enough visual to plausibly be an establishing shot for an environment.
It just doesn’t look like the Mustafar that has been established in canon.
I say put Kylo forest fight scene where the broom boy scene was in TLJ (after all, he is pissed off about Luke totally faking him out), cut to credits with Kylo holding the Holocron.
Episode 9 begins with kylo seeking and finding Palpatine. Or establish in the Crawl that he has already found him.