Preheat oven to 350 degrees. 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.
Add the flour, cocoa powder, baking soda and salt to the other mixture and mix on low speed, just until combined.
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 ¾ cups of the chips into the cookie batter, setting the remaining chips aside in reserve.
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.