Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper. Set aside.
In a large mixing bowl, beat the butter, granulated sugar, and brown sugar until creamy and light in color. Add the eggs one at a time. Then, pour in the vanilla and mix. Scrape down the sides of the bowl.
In a small mixing bowl, whisk together the flour, cocoa powder, baking powder, and salt. Slowly add the flour mixture to the wet ingredients until combined.
Stir in the graham cracker cereal, mini marshmallows, and chocolate chips with a rubber spatula.
Scoop 1/4 cup of the cookie dough from the bowl and then use your hands to form it into a ball. Place on the prepared baking sheet and gently press down so the bottom is a bit flat. Repeat with the rest of the cookie dough, spacing the cookies 3 inches apart.
Bake for 15-18 minutes or until the cookies are set.
Remove from the oven and allow to cool on the baking sheet for 5 minutes. Then transfer the cookies to a wire rack to cool completely.