I made 5 round cakes in effort to have at least two I could work with. Made silver white cake from scratch, but really any cake can be used. Froze cake to make it easier to work with. Used one round as face and cut out an ear and his hair spikes (is that hair?!). Froze pieces again then stuck them together with frosting. Froze again.
I actually did the blue frosting first and as I shaped him I refroze several times to prevent errors. I did the white frosting next and then the peach. I used detailing gel to outline, create nose, and eyes. I was so tickled with how this Sonic Birthday Cake turned out on my first try.