1. Whisk together flour, cocoa, salt and cinnamon; set aside.
2. Using an electric mixer, cream butter and sugar until light, about 2 minutes. Beat in eggs and vanilla. Working in two batches, add flour mixture and beat until just combined. Divide dough in half and wrap pieces in plastic wrap, flatten into disks and chill 1 hour or overnight.
3. Heat oven to 350 degrees F. On a floured surface roll dough to 11/4-inch thick. Cut with a 5-inch gingerbread man cookie cutter and transfer to unlined baking sheets. Reroll scraps once. Bake until cookies spring back when touched, about 12 minutes. Cool on wire racks.
4. Prepare 1 recipe of Royal Icing. Transfer to a piping bag fitted with a #2 plain tip. Decorate with lines for a skeleton. Pipe an outline of a skull and circles for eyes and mouth; flood face with icing. Sprinkle some with sanding sugar. Dry completely.