Make the cookies: Whisk the flour, cocoa powder, cinnamon, baking soda, baking powder and salt in a medium bowl. Beat the butter, granulated sugar and brown sugar in a large bowl with a mixer on medium-high speed until light and fluffy, about 5 minutes. Beat in the egg and vanilla until creamy, 1 to 2 minutes. Reduce the mixer speed to low. Gradually add the flour mixture and beat until combined, about 2 minutes. Divide the dough in half; pat each piece into a disk and wrap in plastic wrap. Refrigerate until firm, 1 hour.
Roll out each dough disk between 2 sheets of parchment paper until 1/4 inch thick. Refrigerate until firm, about 2 hours.
Position racks in the upper and lower thirds of the oven and preheat to 350 degrees F. Line 2 baking sheets with parchment paper. Cut the dough into shapes using a 4 1/2-inch gingerbread man cookie cutter and arrange 2 inches apart on the prepared pans. Reroll the scraps and cut out more cookies. (If the dough is too soft, freeze 10 minutes before cutting.) Refrigerate until firm, 15 minutes. Bake, switching the pans halfway through, until the cookies are set but still soft, 15 minutes. Let cool 10 minutes on the pans, then transfer to racks to cool completely.
Make the icing: Beat the confectioners' sugar, meringue powder and water in a bowl with a mixer on high speed until smooth and thick. Transfer to a resealable plastic bag and snip off a corner. Pipe skulls and bones onto the cookies. Let set 30 minutes.
To decorate the cookies, first make the outline of the skull, eyes, nose, mouth and bones. Then thin some icing with a little water and pipe into the outline of the skull; use a toothpick to help.