When my son said he really wanted a Transformers cake, and we looked at the grocery store, we were both disappointed at the "store bought" one. I love to make cakes, but after some stressful years, I told myself I'd always go store bought to ease the stress! I changed my mind with this one and I'm glad.
My son had a Transformer tag he kept off of a pair of shoes that had a 1/2 Autobot and 1/2 Decepticon face and he told me he really wanted that on his cake. I enlarged it on our copier, glued it to a piece of tag board, laminated it and cut out the pieces to make a "puzzle" of sorts.
Once I made the sheet cake (it was a large pan so I used 2 cake mixes, one vanilla, which I tinted red, and one chocolate, which I darkened with black food coloring gel and swirled them together for a red/black tye dye effect) and iced it. I let the icing get a little bit of a crust and then placed the "puzzle" pieces on the cake and outlined them with a toothpick (sort of like pumpkin carving kits!)
When I had the outline done, I filled in the shapes with the appropriate tinted icing with my piping bags (I used star tips to fill in the gray). I also piped in a few flames on each side to match Optimus Prime's arms. I found key-chain Transformers, took the chains off and placed them on top for an extra special touch. I did my best at writing "Transformer" style font for the "Happy Birthday".
I think my son and his friends enjoyed it, even though it didn't last very long! It was a little more time consuming than I had planned but I'm glad I took on the challenge. Hope you like it!