In advance use tip 6 and Lemon Yellow icing to make 6 Shaggy Mums on vanilla wafers; make extras to allow for breakage and let dry.
Bake and cool 2-layer cake. Use spatula to ice top of cake white. Use icer tip 789 and pink buttercream icing to ice bottom layer of cake; repeat for top half of cake using green icing. Use tip 21 and yellow icing to pipe a shell border between green and pink sections on side. Attach Shaggy Mums to cake top with icing.