Well, there are 2 alternatives.
You buy some vanilla ice cream, mould it into a big oval and a small oval (for the head), get chocolate buttons/biscuit pieces/whatever's suitable for the prickles and stick them in all over except on the face. 2 chocolate buttons for the eyes and sprinkle face (or all body if not using buttons) with cocoa powder. Put back in the freezer and remove about 15 mins/half an hour before eating.
Alternatively, you could just pop down to your local gelateria artigianale and buy one.
I have done both. Needless to say the gelateria one was more aesthetically pleasing.
Alternatively you could make a dinosaur. It uses the same principle but there is a lot more scope for "creativity" as you just invent the species on the basis of the result.