Line a large baking tray with grease proof paper.
Chop the dark chocolate and place in a bowl. Microwave for 30 second bursts, stirring, until the chocolate is melted and smooth. Alternatively place bowl over a saucepan of barely simmering water and allow the chocolate to gradually melt.
Place the candy melts in two bowls and melt using same method. Transfer each to a piping or zip lock bag.
Spread the melted chocolate over the prepared tray and quickly, pipe spirals of the candy melts over the chocolate.
Drag a skewer through the spirals to create a marbled spider web effect. Sprinkle the googly eyes, jelly eyes and any sprinkles you like over the chocolate while it is still wet.
Chill in the fridge until set
Break into smaller pieces and enjoy!