Mix cake according to manufacturer’s instructions, adding in 1.5% rum flavor and 0.4% lime flavoring. Measure out 3 pounds batter, deposit 1 pound into a sprayed and papered 8-inch cake pan. Repeat two times to make 3 cakes total. Bake at 350F until cake springs back lightly when touched. Let cool completely. Fill with keylime pie filling and ice cake with black buttercreme. Using different styles and sizes of star tips, pipe rosettes in different sizes on the sides and top of cake. Finish with sugar skulls.