Halloween is a week-long annual event in eRO in which activities in the event give the opportunity to earn special time-limited headgear sets.
There is an a NPC—codename Nikolas (@warp niflheim 200 185). Talk to him to be warped to a map filled with Gold Porings and Hollow Porings. Kill them and collect Halloween Tickets which you can use to redeem a Halloween Box. You'll have a chance to get one (1) of the Halloween-themed headgears from the Box.
A mechanism that's used in the Temple is repeated, and the custom dungeons whereby every X kills of monsters on the designated map, the King will spawn. In this case, every X Gold Porings and/or Hollow Porings killed, a Hollow King will spawn. The Hollow King has his own set of drops as well, even more tickets too!