Preheat the oven to 350°F. Line two large baking sheets with parchment paper and set them aside.

In a large mixing bowl, use a hand mixer to mix the cake mix, eggs, and oil until well combined.

Using a rubber spatula or wooden spoon, fold in the M&Ms, chocolate chips, mini marshmallows, crushed pretzels, and sprinkles.

Using a large cookie scoop, scoop the cookie dough onto the prepared baking sheets, leaving at least two inches between each cookie, as they will spread while baking. If desired, top the cookies with extra M&Ms and chocolate chips.

Bake for 10-12 minutes or until the edges are set.

Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to finish cooling.