Line a 9x13-inch pan with parchment paper; set aside. Pour cereal into a large mixing bowl; set aside.
In a saucepan over medium heat, combine marshmallow creme and cashew butter until smooth. Remove from heat and mix in collagen and protein powder until well combined.
Pour over cereal and gently fold until fully incorporated.
Press into the bottom of the prepared pan and let set before cutting into bars.