In a large bowl, combine softened butter, brown sugar, and granulated sugar together on medium speed with a hand mixer or stand mixer until blended and fluffy. Add in eggs and vanilla and mix until fully blended for another minute. Set aside.
In a medium bowl, whisk together all-purpose flour, cocoa powder, baking powder, salt, and instant coffee granules until well blended.
Add the flour mixture to the butter-sugar mixture a little at a time and mix on low speed until fully combined, about 3 minutes. Stir in semi-sweet chocolate chips and Halloween M&M candies with a wooden spoon until evenly combined.
Cover the bowl with plastic wrap and refrigerate it for 30 minutes.
Preheat the oven to 350 degrees Fahrenheit. Line a baking sheet with parchment paper and scoop cookie dough into 1 ½ inch cookie balls, spacing them out 1-2 inches apart, then flatten with your fingers to even them out a bit. Add candy eyeballs to the top of the cookies using a combination of small, medium, and large eyes.
Bake for 8-10 minutes until the edges are set and the middle is soft; they will not look done but will set once out, don’t over bake!
Remove them from the oven and let them cool on the cookie sheet for 3-5 minutes before transferring them to a cooling rack.
Store in an air-tight container at room temperature for up to a week, if they last that long!