Preheat oven to 350° F. Line a baking sheet with parchment paper.
In a large bowl of a stand mixer, combine the butter and sugars and beat for 3-4 minutes, until light. Add eggs and vanilla and mix well.
1 cup salted butter, 1 cup granulated sugar, 2/3 cup firmly packed light brown sugar, 2 large eggs, 2 teaspoons vanilla
Add the flour, cocoa powder, baking soda and salt to the other mixture and mix on low speed, just until combined.
2 cups all-purpose flour, 2/3 cup Hershey's special dark cocoa powder, 1 teaspoon baking soda, 1/4 teaspoon salt
In a separate bowl, combine the Halloween chips, white chocolate chips, peanut butter chips, and mini Reese's Pieces and give them a quick stir so they are evenly distributed. Gently stir or fold in 1 3/4 cups of the chips into the cookie batter, setting the remaining chips aside in reserve.
1 cup Halloween baking chips, 1/2 cup peanut butter chips, 1/2 cup white chocolate chips, 1/2 cup mini Reese's Pieces baking candies
Scoop approximately 2 tablespoons of cookie dough for each cookie and shape into balls by rolling between the palms of your hands. You might need to refrigerate the dough for 30-60 minutes in order to work with it as it is a very soft dough, although I can usually skip that step as long as I work quickly. Once the dough is shaped, place the balls on the prepared baking sheet 2 inches apart and bake for 8-10 minutes, just until set. Do not overbake.
As soon as the cookies are removed from the oven, press a few of the reserved chocolate and peanut butter chips into the top of each cookie. It's a total vanity move but adding the extra chips at the end makes the cookies look so pretty and festive. Transfer to a wire rack to cool completely and store in an air-tight container.