I did this Ninja Turtle cake for my nephew’s fifth birthday. This is his favorite turtle (Leonardo I think). It actually was not hard to do. I used instructions for making a 3-D Bust cake. I have made this type of cake before as Spiderman and decided to try it out on a Ninja Turtle. The head is actually not edible. It is a Styrofoam wig head (purchased at a beauty supply store).
I did have to build up the nose and mouth area to look like a turtle. I tried rice crispy treats but they fell off so I used cooked biscuits. The cake is the chest and shoulders. You need two 10 inch cakes and one 8 inch. Stack to two 10 inch cakes on top of each other. Place the head on top of these. Put a dowel stick through the top of the head and down through the cakes to keep it in place. Cut the 8 inch cake into fourths. Use two pieces for each shoulder.
Ice the entire cake in icing (including the head). The mask is fondant. I just colored it, rolled it and cut it out (free-hand). Hope this helps anyone who would like to make a cake like this!