Line a rimmed baking sheet with aluminum foil lightly sprayed with cooking spray, and set aside.
Add white chocolate melting wafers to a microwave safe bowl, drizzle with 1 tsp vegetable or coconut oil, and microwave in 20-30 second increments, stirring after each time, until smooth.
Add milk chocolate chips to microwave safe bowl, drizzle with 1/2 tsp vegetable or coconut oil, and microwave in 20-30 second increments, stirring after each time, until smooth. Stir in brownie mix.
Add colored candy melts to microwave safe bowls (each color gets their own bowl), add 1/2 tsp vegetable or coconut oil, stir to coat, and microwave in 30 second intervals, stirring after each time, until smooth.
Use a rubber spatular to spread out white chocolate in the baking sheet in an even layer. Dollop the milk chocolate mixture in random spoonfuls, onto the white chocolate. Use a toothpick or wooden skewer (the flat end is perfect for this) to swirl the two chocolates together.
Drizzle colored candy melts in vertical lines over the chocolate (you could also drop them by spoonfuls in a non-pattern), and use a toothpick or skewer to swirl them into the mixture as well.
Top with sprinkles and candy (if using), and refrigerate several hours, or until hard and firm.
Break into pieces and serve.