My son wanted a Marvin the Martian cake for his 5th birthday so I researched, got some ideas, and took a shot at it. I made two 9×13 cakes, one chocolate and one vanilla. After freezing them, I carved them (with the help of my wonderful husband), stacked them, and gave them a good crumb coating. Then back to the freezer they went for about a day, and then out the day before his party for to cover with fondant.
I made and colored marshmallow fondant a few days prior to covering the cake, and when I needed the fondant, it was ready. Covering the cake wasn’t too hard, and I used black icing gel for the details. It turned out pretty good, and he was very happy with it, as was I.