Next years Halloween events achievements.
I would like to know about this as well. More specifically, is there anything this year that’s “this year only” as in I can’t finish it next year?
No way to tell for sure at this point with no precedent. The closest we have is that GW1’s events were generally built around repetition, with each succeeding holiday event being basically the same thing as before with 1-2 new things added and one unique item (though the unique items are now available every year).
It is a lot easier on the developer, especially if they’re going to remain as active in adding content to GW2 as they are claiming, to mainly “bolster” the holiday event each year rather than rebuild an entirely new one. As a result, I’m inclined to speculate that most of this content, particularly the stuff in the Mad King’s Realm, will indeed be available in future Halloweens. That said, I would recommend trying to finish as much as you can during this event, just in case.
Some comments from a couple of the devs (sorry no links) earlier indicated they haven’t decided how they’ll handle it yet.