Runners competing in the 20 anniversary Walt Disney World Marathon – registration opens today – will experience several unique features, including a special 20th anniversary medal, new entertainment elements and a new post-race party.   To mark two decades of the Walt Disney World Marathon, the 2013 marathon, which anchors the Walt Disney World Marathon Weekend presented by Cigna, will have enhanced entertainment at Mile Marker 20 to celebrate the 20th anniversary. And the finishers will take home a specially-designed 20 anniversary Mickey Mouse medal, plus they can celebrate their achievement at a new post-race party at Downtown Disney.