At the moment there is little information on the event. However, it will a culmination of all the preceding pin events (there was on in the MK on 2/23; one in MGM in March, an event in April at the AK, a cruise in May,etc.).
There are usually special pins released (at the Princess Ball event on 2/23 there were six princess pins and an evil queen). There is a charge to access the event (25.00 for the Princess Ball but the AK event is $125 due to it being a dinner event after AK closes). We also got a special Walt with Tink pin and lanyard at the Ball.
At the moment, information is only available on the MGM event and the AK event.
You can call Epcot Special Events for more information or to be placed on the mailing list. 407/827-7600
Email me if you have specific questions.
Cyn