When my kids were little, I had two booklets full of cut-up cakes. Bake a cake, cut it up and cover the whole thing with mountain frosting made in the double boiler. Divide the frosting and tint portions first, then use coconut and other additions to trim. They have all looked fantastic. Here's a link to instructions on making the witch. It starts with a single 9" square cake.
https://homanathome.com/2019/10/witch-cut-up-cake/
Well, sort of instructions. This cook is using buttercream and icing bag, but you can easily use frosting.