The Havenworlders learn of the Human tradition of Halloween. Some Human nations have it as the day of the dead, some have it as All Hallow's Eve, either way, it's a lot of fun for the Humans, not so much for Havenworlders, and most other Deathworlders to be honest. As Humans get ready for their holiday with skulls, frightening movies, costumes, and treats, many nations tremble wondering what will happen when that festival arrived. -- DaniAndShali
This is Halloween! This is Halloween! Halloween! Halloween! -- Incredibly catchy Human festival song.
Humans have an incredible fascination with things that could kill them. So much so that they invent things that could kill them if they actually existed. They invent things to scare themselves with. Then, on a specific day of their calendar, they all decide to bring those fears into the open and celebrate them. The undead, the monsters of their assorted fictions, deadly beasts, or random concepts with the word 'sexy' tacked onto the front... All of them come out when the Humans celebrate this one day of horror.
As the reader might understand, the whole 'fear factor' involved in that holiday does not mesh well with Havenworlders. This has lead to 'Deathworlder Zoning', so that resident Havenworlder populations can simply avoid all the weird Deathworlder horror elements scattered all over those areas.