Make leaf 1 day in advance. Tint white fondant 36 1/2 oz. gray and 1 oz. blue. Knead 1/4 teaspoon Gum-Tex into 1/2 oz. gray fondant.
Roll 1 1/8 in. ball of gray fondant. Use fondant roller with blue guide rings to roll out fondant 1/16 in. thick. Use straight edge of largest (1 1/4 in. x 2 1/4 in.) leaf cut-out to cut leaf. Use fondant roller to elongate leaf to 3 3/4 in. long. Use small veining tool from set to add vein and details on thin shaping foam.
Use royal blue icing color and water, royal blue icing color, white-white icing color and water, and white-white icing color and water to make paints in candy melting tray. Use brush and light blue paint to paint details on leaf. Use brush, dark blue paint and white paint to add more details until desired look is achieved. Reserve paints.
Use knife to cut notches, 1/4 in. to 3/8 in. deep, from leaf. Let dry, about 24 hours, in large concave section of wave former tray.
Make flower also 1 day in advance. Use fondant roller with blue guide rings to roll out blue fondant 1/16 in. thick. Use straight edge of third smallest (1 7/16 in.) round cut-out to cut seven circles. Place one circle in cornstarch-dusted small (2.5 in.) flower forming cup. Use small ball tool to thin edges of remaining circles on thin shaping foam. Fold circles in half and then in half again. Use damp brush to attach folded circles to whole circle in flower forming cup. Use veining tool to separate petals, if needed. Let dry, about 24 hours.
Make cake. Prepare batter following recipe directions. Bake and cool two 6 in. cake layers. Prepare buttercream icing following recipe directions. Level, fill and stack cake on cake circle, for 2-layer cake, 5 in. high. Use spatula and icing to ice cake lightly. Reserve remaining icing.
Cover cake with fondant. Use fondant roller with orange guide rings to roll out 36 oz. gray fondant 1/8 in. thick. Cover cake with gray fondant.
Paint feather on cake. Use brush and reserved paint colors to paint feather on side of cake. (If needed, hydrate paints with a few drops of water.) Begin with white paint and then add light blue and dark blue. Add more white for details. Let dry, 10 to 15 minutes.
Attach decorations. Prepare thinned fondant adhesive following recipe directions. Use brush and thinned fondant adhesive to attach feather to side of cake next to large, painted on feather.
One of the simplest techniques for decorating with fondant is to create cut-outs. Fondant shapes can be applied to lay at on the surface of a treat or dried so that they hold their shape when used as a topper.