Preheat your oven to 350 degrees F (175 degrees C) and line a 12-cup muffin tin with liners.

In a liquid measuring cup, stir the espresso powder with 1/2 cup hot water and allow it to cool.

In a large bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt.

Using a stand mixer, combine the egg, milk, oil, and vanilla at medium speed until well blended.

Gradually add in the sugar and the cooled espresso mixture, followed by the dry ingredients, mixing until the batter is glossy and smooth.

Fill each cupcake liner about two-thirds full with the batter.

Bake in the preheated oven for 18-20 minutes, then allow to cool completely.

Once cooled, scoop a small hole from the top of each cupcake and fill it with a mixture of strawberry jelly and a few drops of red gel food coloring.

In your stand mixer, beat the softened butter until smooth.

Gradually add the Marshmallow Fluff and confectioners' sugar, mixing until fluffy.

Add vanilla and salt, ensuring a light and airy frosting.

Generously frost the top of each cupcake with the fluffy marshmallow frosting.

Refrigerate the cupcakes until set.

Using the remaining frosting, create a fun stencil with parchment paper and roll the edges in crushed chocolate graham crackers or chocolate wafer cookies.

For the final touch, drizzle the reserved jelly on top of the cupcakes to create spooky 'bloody' fangs.