Line a baking sheet with parchment or waxed paper. Place the granulated sugar in a large mixing bowl. Add the meringue powder and stir to combine. Add the water one teaspoon at a time, mixing with your hands. The sugar should feel like barely damp beach sand, forming a clump with finger indentations when squeezed in your hand.

Pack the prepared sugar into the mold, and then turn over quickly onto the parchment. The formed skull should come out of the mold in once piece. Allow to dry overnight.

Once the sugar skulls have dried, decorate using a piping bag filled with royal icing. Allow the decorated skulls to dry overnight. Sugar skulls will keep indefinitely, provided they are stored in a dry environment.

Note: If the sugar skull crumbles, return the prepared sugar to the bowl, and add one more teaspoon of water. Remix, and then pack again into the skull mold. Unmold and dry overnight.

To make the royal icing, combine the powdered sugar and meringue powder. Add the water one tablespoon and mix at a time until your icing is thick, yet smooth in consistency.

If you would like colored icing, divide the icing into portions, and add the gel color of your choice, and mix well. The icing should be thin enough to pipe using a piping back, but not runny. You can adjust the consistency by either adding a bit of water to make thinner, or a teaspoon of powdered sugar to make thicker.

Decorate the skulls with the royal icing and a piping bag. Allow to dry overnight.