Preheat your oven to the temperature specified on the brownie mix box, usually around 350°F (175°C).
Grease your 13x9 inch baking pan with non-stick spray or line it with parchment paper.
In a mixing bowl, combine the brownie mix with water, oil, and eggs. Stir until just combined.
Chop your assorted candy bars into small pieces and gently fold them into the brownie batter.
Pour the brownie batter into the prepared baking pan, spreading it evenly.
Bake as instructed on the brownie mix package, typically around 25-30 minutes.
Once baked, remove from the oven and let cool for at least 10-15 minutes before slicing.
Cut into squares and serve!