Sift 2 1/2 c powdered sugar into a bowl. Combine 1 tsp light corn syrup, 2 eggs and 1 tsp vanilla in another bowl. Add liquid mixture to sugar. Use your hands to mix until you get a soft dough. Shape it into a big ball and stick in the refrigerator for about 1 hour. Dust a dry work surface and hands with cornstarch. Break off chunks of dough and form into skull shapes or use skull molds.