Many forms cannot be adequately done with the mass possessed by a Human sized character. It is for this reason that a character with Shape Shift can use his/her power to absorb mundane Shadow Material into him/herself to take on sufficient mass for the desired form. For example, when the Demon Servant, Gryll, came to Merlin to take him back to the Courts he lacked sufficient mass and size to carry Merlin on his back. Gryll then proceeded to absorb some furniture from Merlinís room in order to gain the desired size and mass.
The Shadow Material which the character absorbs cannot be living material, nor can it be magical. It must be considered generally mundane in the Shadow in which the material exists in order for the Shape Shifter to be able to assimilate it into themselves. This process increases the time required to Shape Shift greatly, adding up to 15 minutes, and if the Shape Shifter wishes to then go to a form with less mass/size he or she will have to expel the absorbed matter first, which will take twice as long as absorbing it. (apart from being pretty gross to watch) Note that the character may not decrease their mass less than their smallest Basic Formís original starting total.