The Halloween Event is an annual occurrence in the "City of" franchise. It runs for a few weeks straddling October 31st, every year except for 2005. The event features special enemy groups such as the Unseelie Court, and some creatures only seen in Croatoa visit other zones.
Other hallmarks of this event are Trick or Treating, Giant Monster hunting, badge hunting, and starting in 2008, the Zombie Apocalypse. The 2009 Halloween Event upgraded the Zombie Apocalypse to the Deadly Apocalypse, with new mechanics and new enemies to fight. Some changes in the rest of the event were also made. In 2010 a special tip mission was added (Whispered Rumor) in which players could earn badges for its completion as well as the Meticulous Accolade. And in the 2011 event, a Holiday Trial was added in which players assault a mad scientist's haunted mansion.