I made this Spongebob cake from a regular rectangle cake pan. First, I cut a piece of paper the same size as the cake and used it as a template to figure out how to cut the cake to make the legs and arms.
I cut off approximately 2 inches from the bottom and used each piece to make the legs. I cut off about 2 inches from each of these piece, turned it sideways, and that was his feet. For his body, he is really more of a square than a rectangle and he angles in at the bottom, so I cut off a triangular piece on each side and used this for his arms.
I covered the entire cake with the star tip using buttercream icing. You can ice him ahead of time, but I would wait until that day to do the final detail – the black icing may bleed on the white. I added the plastic googly eyes as well. TIPS: Make sure you put a dot of icing under his legs and arms to anchor them to the cardboard.
You also need to try to ice the inside of the legs before anchoring them down; otherwise, it will be very difficult to ice the insides of his legs because they are so close together.