Combine peanut butter chips, corn syrup, butter & mini-marshmallows in a microwave safe bowl. Heat on high 2-2-1/2 minutes, stirring in between each minute until almost completely smooth.
Remove from microwave & immediately add cereal. Working quickly - fold cereal into melted mixture until coated & mixed thoroughly.
Transfer to parchment lined 9x13 pan & press into a flat even layer. Let sit at room temperature for 1-2 hours to firm or if you are like me & can't wait- refrigerate 20 minutes to chill until firm.