Heat the sugar and corn syrup in a large saucepan over medium heat, stirring constantly until the mixture just begins to bubble, then immediately remove from the heat to avoid making the bars too firm.

Stir in the peanut butter until smooth and fully combined.

Fold in the crispy rice cereal until all of the cereal is evenly coated.

Gently press the mixture into a greased 9x13-inch pan. Create a smooth, even layer, without packing it down too firmly.

Melt the chocolate chips and butterscotch chips together in a microwave-safe bowl, working in 20–30 second intervals, stirring between each, until smooth.

Pour the melted mixture over the cereal layer and spread evenly.

Let the bars sit at room temperature until the topping is set, about 1 hour, then cut into squares and serve.