If you can paint or draw, you'll be able to have a crack at a novelty cake. Modelling sugar-paste into various characters can be really frustrating and even if you are a first class sculptor, with well known characters, the smallest difference in the configuration of facial features can make Hello Kitty look like 'Hi Kitty' you see on fake merchandising. With painting directly onto a cake and mapping out where the lines are going with a pin or similar you're that much safer.
When I was asked to do a Dora cake, I didn't know who she was, with a little youtube research it turns out she is the kind of cartoon I would have loved to watch as a kid. Dora, explores some place new every episode finding people she can help and teaching kids Spanish at the same time, cute!Wish I had a little monkey friend.