Preheat the oven to 350°F (180°C). Line a cupcake tray with paper cups.
Sift the flour with baking powder, baking soda, salt, and cocoa powder in a large bowl. Add the sugar and chocolate chips and combine with a hand whisk.
Dissolve the instant coffee with the boiling water.
Add the egg, oil, buttermilk, vanilla extract, and the coffee. Mix everything until you get a smooth batter.
Pour the mixture into the cupcake paper cups, filling each one ¾ full. You can use an ice cream scoop or a pitcher.
Bake in a preheated oven at 350°F (180ºC) for 20-25 minutes, until a toothpick inserted into it comes out clean. Let cool.
While the cupcakes are baking, make the buttercream (see recipe below) and set aside at room temperature.
Violet monster decoration: Dye some violet buttercream with the violet food color. Place in a piping bag with a star tip (Wilton 6B or similar). Decorate by making blobs from the outside to the inside of the cupcake.
Garnish with edible eyes and sprinkles.
Mummy decoration: Stick the edible eyes on the center of the cupcake with a dot of buttercream.
Place the uncolored buttercream in a piping bag with an adapter and a ribbon tip (Wilton 105 or Ateco 45). Set your piping tip parallel to the cupcake. Draw lines with the buttercream from side to side, lifting your hand as you draw the ribbons. Cover all the sides of the cupcake around the eyes.
Frankenstein decoration: Color some green buttercream. Place a small spoonful of buttercream in the center of the cupcake and spread it up and down so that it looks like a long face.
Color a little black buttercream as shown in the recipe below. Place it in a small piping bag, and cut a small tip. Decorate the hair and mouth by making zigzags with black buttercream. Add eyebrows and edible eyes.
Ghost decoration: Place the uncolored buttercream in a large piping bag with a large round tip (Wilton A1, Ateco 809, or a larger one). Place the tip vertically on the cupcake. Press and lift slowly to create a large dollop.
Place black buttercream in a small piping bag and cut a small tip. Use it to make small and long circles for the eyes and mouth of the ghost.