Halloween Events carry forward from year to year. I don’t see any new ones for 2017. The Event is 34 days and will end on November 27, 2017.
The Halloween 2015 Event began with the same quests from the 2014 Halloween Event. If you started this quest string but did not finish it your first quest will be where you left off last year. If you managed to open the Witches Athenaeum it will return opened to the top of your First Floor above the Fortune Telling Room:
Witch’s Athenaeum Quests
I have moved the Witch’s Athenaeum quest to their own page.
It looks like you must complete this quest string to get the Pumpkinshadow Castle quests.
Pumpkinshadow Castle Quests
I have moved these quests to their own Pumpkinshadow Castle page.
Lord of Despair Quests
This is the new quest string for 2016. I have created a page for the Lord of Despair. I have not seen any sign of it for 2017.
GI has confirmed that the 2017 Event is just a repeat of previous years with no new quest strings. If you finished those strings you will start at the beginning with Witch’s Athenaeum and Pumpkinshadow Castle will be closed.