Line a pan with parchment.
Measure rice cereal into a medium size bowl and set aside.
In a saucepan, melt butter and marshmallows together.
Pour the marshmallow mixture into the rice cereal and stir until combined. Add sprinkles, marshmallows, and candy-coated chocolates to the rice cereal mixture and stir.
Spread into the parchment-lined pan. Add any additional candy, sprinkles, or marshmallows to the treats. Use another pan to press down and flatten the treats.
Allow the treats to set. After they've set, remove the treats by lifting the parchment paper from the pan. Cut the treats into rectangles, making sure to cut straight down.
