Last year, Buddy requested a Spider-man cake. And, he's already told me that he wants a Hawkeye cake next year, and that his little brother would like an Iron Man cake for his birthday (in October).
To start I made a regular two-layer cake and coated it with bright green buttercream. I piped on the hair and face with a writing tip using black icing. For the teeth, I used a basketweave tip backwards, so the teeth look smooth with jagged edges. Then I piped Hulk's eyes in green icing with a writing tip. Super easy for how awesome it turned out!