Preheat oven to 350°. Grease a 13" x 9" baking pan with cooking spray. In a large bowl, prepare cake mix according to package directions. Pour batter into prepared pan.

Bake cake until a tester inserted into the center comes out clean, 25 to 30 minutes. Let cool.

In a large bowl, using a handheld mixer on medium-high speed, beat cream cheese and butter until light and fluffy, 2 to 3 minutes. Add confectioners’ sugar and beat until combined. Beat in vanilla and a pinch of salt.

Crumble cake into frosting and mix to combine. Form into 1 ½" balls (about 34 total). Arrange on a baking sheet and refrigerate until firm, about 1 hour.

To make hooks, place 34 cereal pieces flat on a baking sheet. Hold one of the remaining cereal pieces upright and dip bottom into melted white candy. Attach to the center of a cereal piece on baking sheet. Repeat with remaining cereal pieces.

Dip one-third of cake balls into melted green candy, one-third into melted red candy, and remaining third into melted white candy, tapping off excess. Before candy hardens, sprinkle some cake balls with sanding sugar. Return to baking sheet and let set, 15 to 20 minutes.

Transfer three-quarters of remaining white candy to a resealable plastic bag; cut off a tiny corner. Pipe designs on balls; sprinkle with sanding sugar before candy hardens. Dip hook bottoms into remaining white candy (reheating if necessary). Top cake balls with hooks.