Make fondant peacock cut outs two days in advance. For tail, tint 1 oz. fondant green. Knead 1/4 teaspoon Gum-Tex into fondant. Use fondant roller and pink guide rings to roll out green fondant 1/16 in. thick. Use knife and pattern to cut tail.
For head and wings, tint 1/2 oz. of fondant teal. Knead in 1/8 teaspoon of Gum-Tex. Use fondant roller and pink guide rings to roll out teal fondant 1/16 in. thick. Use knife and pattern to cut head and wings (cut two wings; reverse one for left side).
Let all cut outs dry overnight on cornstarch-dusted surface.
Make head and feather details one day in advance. Prepare royal icing. Tint portions black, violet, dark blue. Reserve some white.
For head feathers, place parchment paper over head pattern and fondant head over parchment paper. Use tip 2 and black icing to pipe feathers. Let dry. Use tip 2 and white icing to pipe in beak and whites of eye; pat smooth with finger dipped in cornstarch. Use tip 2 and black icing to pipe dot pupil. Let dry.
For tail feathers, use tip 2 and violet icing to pipe spine of feathers and background eye areas. Use tip 1 and dark blue icing to fill in eyes. Use tip 1 and violet icing to pipe branch lines on feathers. Use tip 1 and white royal icing to outline blue areas of eyes. Let dry.
Make cupcakes. Prepare cupcake batter following recipe. Bake and cool cupcakes. Prepare buttercream icing. Tint teal. Use spatula to ice top of cupcakes smooth. Insert head and tail; position wings.