Spray a Bundt pan generously with non-stick cooking spray. Set aside.
Melt butter in a large saucepan over medium heat. Add marshmallows and jello. Stir until melted and completely combined. Add cereal and stir until it's combined with the marshmallow mixture. Quickly pour into the prepared pan. Press it down into pan with greased fingers or a greased spoon. Smooth top so it's level. Let cool about 1 hour.
Invert cake onto a large plate. Melt chocolate chips in a small microwave safe bowl with the microwave set on high for 1 minute. Stir until smooth. Pour into a disposable plastic pastry bag. Cut the tip of the bag to create a very small hole. Drizzle chocolate over cake. Repeat process with remaining candy melts, doing the red first and then the pink last. Add sprinkles to the top right away before the chocolate sets. Slice and serve. Store covered at room temperature for 24 hours or in the refrigerator for a few days.