From Guild Wars 2 Wiki
A special event is an in-game festival of an in-game holiday, although they tend to closely follow some real world celebration. They are usually introduced as major features of releases.
 List of special events
|April Fools' Day|
|2013||April 1 - 30||Super Adventure Box|
|2012||October 22 - November 2||Shadow of the Mad King|
|2012||December 14 - January 3, 2013|| Wintersday: The Wondrous|
Workshop of Toymaker Tixx