“The Jester’s Festival kicks off on March 23, at 10:00am EDT. If you’d like to show off your zany side, you can travel to the pavilions that have been set up just outside the cities of Ebonheart, Vulkhel Guard, and Daggerfall. At each location, you will find one of three Jesters in extremely convincing dress up as either King Jorunn, Queen Ayrenn, or King Emeric. Talk to each Jester to receive a uniquely mischievous task once per day for the duration of the festival.”
Completing these quests will see you rewarded with an obnoxious hat, “fun new consumables” (read: probably pranks), trees and standards for your housing plot (what?) and “mementos” including “The Pie of Misrule,” which is unlikely to be the kind of pie you eat.
ESO is also planning on selling festival-themed cash shop articles, including costumes and a jester cap.