Step 1: Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners.
Step 2: In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and pumpkin pie spice.
Step 3: In a large bowl, cream the softened butter with the granulated and brown sugars until the mixture is light and fluffy.
Step 4: Beat in the eggs one at a time, followed by the pumpkin puree and vanilla extract until well combined.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Step 6: Divide the batter evenly among the cupcake liners, filling each about two-thirds full.
Step 7: Bake for 20-22 minutes, or until a toothpick inserted into the center comes out clean. Let the cupcakes cool completely in the tin on a wire rack.
Step 8: For the frosting, beat the butter until smooth, then add the marshmallow fluff. Gradually add powdered sugar until a stiff piping consistency is reached.
Step 9: Pipe tall mounds of frosting onto each cooled cupcake and use mini chocolate chips to create ghost eyes.