Halloween Week is a week-long event that occurs usually at the end of October or the start of November.
The main portion of this event is the special world named GROWGANOTH (GROWGANOTH0 - GROWGANOTH200 are also available). In the world, the player can drop items at the Maw to obtain different Halloween-themed items. Growganoth accepts a few special trades as well, which will always return a specific item back. As of the 2016 Halloween Week, small Eye Of Growganoth-like creatures were added in the worlds, where the player will fly away when he/she comes in contact with the floating free-moving eyes. And hey! here is a quick tip: Higher rarity items dropped to the Maw will return as better event items such as cape tatters or so.