Preheat your oven to 350°F (175°C) and prepare a 9x13-inch baking pan with cooking spray and flour.

Melt 1 cup of semisweet chocolate chips and ½ cup of unsalted butter together in a medium saucepan over low heat until smooth.

Combine the cooled chocolate mixture with 1 cup of sugar, ½ cup of pumpkin puree, 2 large eggs, and 1 teaspoon of vanilla extract in a large mixing bowl.

Whisk together 1 cup of flour, ½ cup of cocoa powder, 1 teaspoon of baking powder, ½ teaspoon of kosher salt, and 1 teaspoon of pumpkin pie spice in another bowl. Fold into the wet ingredients.

Spread the brownie batter into the prepared baking pan and bake for 25–30 minutes.

Allow the brownies to cool in the pan for about 10 minutes before transferring to a wire rack to cool completely.

Combine 1 cup of granulated sugar and ½ cup of water in a saucepan, stir until dissolved, and bring to a boil. Cook until the mixture reaches 240°F on a candy thermometer. Mix in 2 tablespoons of unflavored gelatin until dissolved.

Pipe ghost shapes on top of the cooled brownies using the marshmallow mixture.

Decorate the ghosts with black piping frosting for eyes and mouths.