Trim Wonder Mold cake, taking 1/2 in. all around. Prepare for fondant covering. Place on a foil-wrapped cake circle.
Roll out black fondant 1/8 in. Cover cake; build up fondant around top of mold, 1 in. high x 7/8 in. wide. Cover with another layer of fondant. Trim front half of dress even. On back half of dress, cut triangles, 1 in. to 1/4 in., so it looks torn. Also, cut triangles, 1/4 in. to 1/2 in., up back of dress.