First, preheat the oven to 350 degrees.
Next, place the wrapped Halloween candy in the freezer. This will prevent the chocolate from melting when you unwrap it and chop it up later.
Add the cake mix, eggs, and oil to a large bowl, mix thoroughly.
Then, unwrap the chilled Halloween candy, chop it into bite-sized pieces, and fold 3/4 of the candy into the cookie dough.
Transfer the cookie dough into a 9"x13" pan lined with parchment paper.
Using a spoon, 'spread' the dough evenly across the entire pan.
Top with the remaining ¼ of candy.
Bake the cookies for about 45 minutes, or until the tops of the cookie bars are golden brown.
Remove the cookie bars from the oven and let them cool complete in the pan before cutting into them.
To remove the cookies from the pan, lift both sides of the parchment paper and transfer the cookies onto a cutting board or another flat surface.
Cut the cookies into 1" squares, for a total of 24 cookie bars.
Enjoy!