Okay so hear me out, Halloween has always been my favorite holiday ever since I was a child.

I was thinking of small (doable) things that PA, specifically GM's have control over.

So I was thinking that for 24 hours (the day of Halloween) make it night time in game, and promote people dressing up with their favorite costumes & taking screenshots of them in spooky places!

A trick-or-treat event questline that takes you to all/most of the buildings in a city 'neighborhood'.  Existing NPCs, and maybe add a few extras to fill in gaps.  Add options to trick or treat, to choose individual quest rewards (which could be the small candy things used for buffs or exchanges).  NPCs could comment on class or costume.  Need to equip the obligatory candy bag in the tool slot.

Go a step further and offer costume transformation scrolls, can only trick-or-treat when transformed. Can resuse existing transformation scrolls, including the permanent ones from past events.