In a very large mixing bowl, stir popcorn and cake mix together until well combined.
Place chocolate in a microwave safe bowl and microwave in 25 second intervals until melted and smooth (stirring between each one). Pour melted chocolate into popcorn bowl, reserving a small amount for topping.
Add sprinkles and chocolate candies to popcorn bowl and mix until well combined.
Spread popcorn mixture onto a baking sheet lined with parchment paper.
Drizzle the remaining melted chocolate over the popcorn and top with additional sprinkles. Let stand for 30-45 minutes. Eat immediately or store in airtight containers.