If you want some parts to be shiny (as in the photo above) apply lustre dust* with a dry, soft brush. Apply it before sticking the parts on. Remove excess dust so that it doesn't get all over the cake topper.
*I used White Pearl (Sugarflair) lustre dust.
Roll out the paste to about 2 mm. Indent vertical lines with a mini palette knife or the back of a knife. Let the paste dry for a while - it needs to hold the shape well. Cut out the mouth (see templates). Roll a thin sausage. Stick it around the cut out part.
The small circles around the mouth and on the chest panel are cut out with a piping nozzle.