Place butter in a large pot over medium heat and stir to melt the butter.
Once the butter is melted, add the mini marshmallows to the pot and stir constantly until the marshmallows are melted.
Remove the pot from the heat and turn the stove off.
Add the rice krispy cereal and cereal marshmallows to the melted marshmallow mix.
Stir the cereal and marshmallows until everything is coated and mixed together.
Scoop the rice krispies onto a pan and press the rice krispies down into an even layer (you can use a 8x8 pan or 9x13 pan, if you choose 8x8 your rice krispies will be super thick and if you choose to use a 9x13 pan your rice krispies will be flatter).
Allow the rice krispies to harden for 1 hour and 15 minutes.
Once cooled, cut the rice krispies into rectangles and serve.
Store the leftovers in an airtight container.