Prepare the Frosting: Divide the 1 ¼ batches of American buttercream frosting into seven portions. Mix two portions with green and yellow food gel for a vibrant green frosting. Create black frosting by blending one portion with cocoa powder, milk, and black food gel, ensuring it’s smooth. Color other portions light yellow, yellow, red, and purple for fun decorating options, leaving one portion white for final touches.

Preheat and Prepare the Baking Tin: Preheat your fan-forced oven to 175°C (340°F). Spray a 32 cm x 24 cm baking tin with non-stick cooking spray. Lay the bottom with parchment paper for easy removal.

Melt the Chocolate and Butter: Combine the melted butter and dark chocolate in a microwave-safe bowl. Heat in 20-second increments, stirring until smooth.

Combine the Ingredients: Whisk in the granulated sugar until well blended. Add the six eggs and whisk again. Fold in cocoa powder and flour, ensuring no lumps. Mix in chocolate chips.

Bake the Brownies: Pour the batter into the tin, spreading it evenly. Bake for 30 minutes, or until a toothpick inserted comes out with moist crumbs. Cool for 1 hour at room temperature before chilling for another hour.

Cut the Brownies: Use a 2 ½ inch square cookie cutter to cut out 12 brownie squares. Prepare your decorating space with piping bags filled with colored frostings.

Decorate Frankenstein Brownies: Pipe green frosting around six brownie squares. Use a piping bag for eyes, mouth, and monobrow, finishing with liquorice pieces.

Create Mummy Brownies: Pipe horizontal lines of light yellow frosting on green-frosted brownies for a mummy effect and use black frosting for spooky eyes.

Assemble Spider Monster Brownies: Pipe purple frosting around brownies, then add a black smile, red fangs, and green eyes.

Finalize Dracula Brownies: Pipe a widow's peak and white frosting on Dracula brownies, with spooky eyes and mouth.