Everybody's pretty much new here! We've only been around since August. :) Anyway, this isn't really an event... It's just a place for the Morostide links for trick or treating to go, so that everybody knows that they have somebody they can get stuff from. Have you been around for Morostide on Subeta before?
Basically a few different things happen at Morostide! The two major ones are ToT (Trick or Treating) and the Pumpkin Patch. ToT is that you can visit someone's "house" (i.e. their profile will have links on them or you can use the ToT links I put in the first post) and you will either get a treat (candy, clothing, etc.) or get hexed! Hexes will occur on your HA and can do a number of different things. Usually it just turns your avatar into a monster of some sort temporarily. Also every 5 people that visit your house and get a treat, you will get the same treat! So it's really advantageous to trick or treat with a group so the 5th visitor happens more often. ToT has wait times that usually last a few minutes. The items you get are spread out between users so not every user gives from the same pool. When Morostide first started, it was split up by how many characters are in your username. The past couple of years, however, it's been determined by how many pets you own.
The Pumpkin Patch (located in Shadowglen) opens up about a week after Morostide starts. You go in and pick from 4 pumpkin patches, and you get random items, usually either pumpkin themed foods or clothing, etc. There's also special Jaxon Skelly minions with a new one getting released each year. The items are random between all the patches except for the Jaxon Skelly minions. Those are assigned to one patch each and if you want a specific one, you have to keep picking from the patch it's located in!
I hope that helps/makes sense.