Carefully flow in thinned black icing to create tombstone shape. Let dry overnight. Using thinned white icing and tip 1 to pipe dots around edge of tombstone. Pipe white skull shape and crossed bones using tip 3. Let dry. Using black icing and tip 2, pipe eye holes and nose. Flatten eyeholes slightly with finger dipped in cornstarch. Pipe mouth teeth with black icing and tip 1.