Pathfinder Halloween session

Our group has rotating gms for the most part in a mostly house built setting that's constantly evolving. My turn to run is coming a few days from Halloween so I kind of want to theme at least one of the sessions with it.

Looking for Pathfinder esque fantasy halloween ideas. Im thinking on making the lore related to the first men, the ones that were driven out of their homes and their traditions only really stuck around in places where they were integrated etc which might be why the party hasn't run into them yet since none of them really lived in those areas and the campaign hasnt been near there till recently.

But yeah, the first men used to dress up as Boogums and whatsits and hunt down monsters and evil spirits. Some to simply kill them, others to drive them from their lands for a time, others to thin their numbers and then turn the spirits/monsters against the creatures they're disguising themselves as so that they are too busy hunting eachother to hunt them etc.

However since a majority of the forests in the western half of the continent were cut down and land was relatively tamed (even if a majority left vacant) as they slowly turned into planes so too did the traditions of the people who integrated some of the first men. With safety relatively in hand the festivities mostly became about warding off evil spirits and celebrating the seasonal harvest/bounty and less about the hunt in the towns that celebrated.

With first men refugees being driven out of the mountains due to spreading famine which is causing war amongst the tribes up there (and a dwarven usurper retaking a major hall in the area and making war upon the tribes to dominate/enslave them) I was interested in having the party experience both sides of these traditions. One from the city and one from the Barbarians.

Considering how tame the lands are I was going to have the barbarians interested in purging the wish demon their ancestors imprisoned long ago (it's in some subterranean caverns/tunnels underneath where the town set up), for their hunt this year. However as an honor based society they cannot transgress/invade another tribe who is also warding off evil per their traditions as this would invite bad luck and bad relations with other tribes etc (he who hunts monsters should be careful he himself does not become one etc). So im having trouble figuring out how I want this kind of relationship to work between the two factions... More or less the barbarians are a red herring.