During the 万圣夜 季节性事件, which lasts from October 20 until November 1, several 敌怪 wear costumes that change their appearance, unique enemies spawn, and new items become available via enemy drops or via purchase. 礼袋s also drop, offering random Halloween-themed items, mostly 装饰 or 时装.
The Halloween event is not to be confused with the 南瓜月, a Halloween-themed event.
In the 洞穴 layer:
From any 敌怪:
From 森林 grass:
From harvesting 南瓜s: