Most of the information that explains the sculpting and painting is very much the same as the 'Monster Bunny Rabbit' instructable
The model I have created can be viewed here in the 123D Creature Gallery.
The final models can become a 3D print, for example with IMaterialise or a cardboard print with 123D Make.
Step 1: The Mask's Skeleton
Once I decided how I wanted the design to look I began with selecting the 'create new' button and altering the skeleton. To begin with you are given a very basic shape to play around with. You can create and remove appendages and manipulate these by moving , shaping, posing and scaling, however the symmetry of the skeleton cannot be changed/removed.
For this design I used the shape tool to increase the general size of the model. One thing to remember when shaping the model is to not forget the holes for the nose and for the string/elastic/ribbon to go through as well as the eyes holes.
One must keep in mind that if you make this too complicated to begin with it can limit the sculpting detail and may even refuse to 'bake' at the next stage of development.
It may seem obvious but remember to keep saving your work or you may be disappointed to find your work is not up to date.