There was a concept Max had thought of introducing on the Third Floor, but he scrapped it because he considered it too dangerous for Silver-Rank Hunters.
It was to introduce Undead in the Whispering Pines region. To be precise, it was first to kill people with the creepy sound and then have their mindless husks attack the hunters.
He could have modified their abilities to bring down their danger level, but it was still troublesome, so he scrapped the whole idea.
Instead, he introduced normal monsters in it—though, of course, they were also pretty dangerous and could take down whole cohorts without anyone noticing.
But the situation was still better than dealing with those undead.
[Haha! Don't worry, I didn't actively change things in the world and just let it fill the holes with either the drafts you had or with your mentality. This whole thing was already planned properly, and there were no holes to fill, so why would it add things unnecessarily?]