This episode definitely looks like an interesting one, and even though it's probably a little Farfetch'd to expect anything close to true horror from an SM episode, given the overall tone of the series, based on the preview, this episode has potential to be rather disturbing. Just the fact that Ash, Lillie, and Kiawe (and their Pokémon, it seems) get turned into puppets is already a little disturbing.
It also seems this is going to mostly a Lana and Acerola episode, which I'm all for. Acerola is an automatic win in my book, and Lana is well overdue for a focus episode. Seriously, when was the last time she had one?