Making this cake was a blast! It took a really long time, but it wasn't really difficult. To be honest, the hardest part was making the shape and putting the first layer of icing on him.
To start, I needed to make the shape. For the base, I used a plain circular cake pan. For his head/body, I used a glass bowl that was safe for the oven (that's super important!). For the tail, I didn't have anything shaped like that already, so I just put batter in a glass bread pan and cut it to the right shape after it was baked. It was actually fun carving out the shape, but it was really difficult, since cake is crumbly.
As you can see, if you plan on covering a cake with decorations, the base layer of icing doesn't need to be perfectly smooth.
For the decorating part, I covered the little guy with stars (which took forever), put a face on him. I had extra light blue icing, so I randomly decided to go back over the top part and make some waves crashing up alongside him. Then I added seashells and seaweed to the base.
Here's a close-up of his face: