Preheat your oven to 350 degrees Fahrenheit. Line a 12-cup muffin tin with cupcake liners.
In a large mixing bowl, sift together flour, sugar, cocoa powder, baking soda, baking powder, and salt.
Add the vegetable oil, eggs, buttermilk, and vanilla extract. Beat on medium speed until combined. Gradually add the hot water, beating until the batter is smooth.
Divide the batter evenly among the 12 cupcake liners, filling each about two-thirds full.
Bake for 16 to 18 minutes or until a toothpick inserted in the center comes out clean. Remove and let cool in the tin for 5 minutes. Transfer to a wire rack to cool completely.
For the buttercream, beat softened butter on high speed until creamy. Gradually add powdered sugar, mixing well after each addition.
Add heavy cream and vanilla extract. Continue to beat until light and fluffy.
Divide the frosting into two bowls. Tint one bowl orange and the other black using food coloring.
Fill two piping bags with each colored buttercream. For a swirled effect, place both bags into a larger bag fitted with a large star tip.
Pipe the frosting onto the cooled cupcakes in a spooky swirl.
Decorate with Halloween sprinkles, candy eyeballs, or themed toppers as desired.
Serve and enjoy your delicious Halloween cupcakes!