Like a few other games—namely Team Fortress 2—the MMORPG world of Guild Wars 2 is getting a Halloween-themed update that's set to arrive on October 22. The special content will give the whole world a Halloween theme and is set to run until the midnight of October 31.
The update will include Halloween decorations, mini-games, mini-dungeons, bosses, and a host of dynamic events in what ArenaNet is referring to as the "Shadow of the Mad King," which is planned as the first of (hopefully) many free content packs for the game. Players who participate in these events will receive time-limited achievements that will be unavailable after the event ends.
In addition to the event, the Black Lion Trading Company will be selling Halloween costumes for players to wear during—and after—the season and plus PvP paid tournaments, which we previously detailed here. Many of these updates will become permanent fixtures in the world of Guild Wars 2.
You can read about the updates at the official site.