Line a plate or baking sheet with parchment paper or wax paper (something that will fit in your refrigerator).
In a microwave-safe bowl, microwave candy melts at 40% power or defrost setting for 1 minute. Stir thoroughly. Continue to microwave and stir at 30-second intervals until smooth and completely melted.
For pumpkin candies:
Dip walnut halves into melted orange candy melts and transfer to parchment paper. While the chocolate is still melted, add a green chocolate candy to one end for the "stem." Refrigerate until the candy is set, about 30 minutes.
For mummy candies:
Dip walnut halves into melted white candy melts and transfer to parchment paper. Using a spoon, drizzle more white chocolate over the walnuts to create the look of "bandages." While the chocolate is still melted, add googly eye candies. Refrigerate until the candy is set, about 30 minutes.
For monster candies:
Dip walnut halves into melted green candy melts and transfer to parchment paper. While the chocolate is still melted, add googly eye candies. Refrigerate until the candy is set, about 30 minutes.
Notes
Candy melts: Candy melts are made from sugar, vegetable oil, whey powder, milk solids, salt, colorings, and flavorings. They look and taste like white chocolate but don't need to be tempered the way chocolate does, and firm up quickly and smoothly. You can buy candy melts on Amazon or locally at Walmart, Michaels, or other craft stores. Look in the specialty baking section.
Candy eyes: You'll find candy eyes, which are sometimes labeled as "edible candy eyeballs" or "small icing eyes," in those same places: Amazon or the baking aisle of most major craft stores (especially in the month or two leading up to Halloween).
Yield: The recipe as written makes 36 ounces Halloween walnuts (12 ounces of each of the 3 varieties). Each serving is 1/2 ounce or 6 pieces of candy, so if you make the full recipe, you'll have 18 servings total.
Storage: Store covered in the refrigerator for up to 2 weeks.