Preheat the oven to 350°F and grease an 8-inch round cake pan.
In a mixing bowl, combine the yellow cake mix, pumpkin puree, eggs, vegetable oil, and pumpkin pie spice. Stir until the batter is smooth and no dry streaks remain.
Pour the batter into the prepared pan and bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean. Remove from the oven and let the cake cool completely in the pan.
Spread the vanilla frosting evenly over the top and sides of the cooled cake.
Set the marshmallows upright on the frosted cake to form the ghosts. Use the black decorating gel to draw simple faces on each marshmallow.
Arrange the candy pumpkins around the marshmallows to finish the pumpkin patch look.