Melt butter in a large six-quart dutch oven. Once the butter starts to melt, add the marshmallow creme.
Over low heat, stir to combine. When butter and marshmallow creme are combined add 5 ounces of regular mini marshmallows. Stir to combine.
When the marshmallows are nearly melted remove from heat and add the cereal two to three cups at a time.
With just a few cups left remove from the heat, add the Funmallows and then stir in the remaining cereal.
Pour into a 9x13 pan or a larger lasagna pan. Wet hands and smooth out the top or pat down with the butter wrapper. Let cool before cutting and serving.
Notes
Use 8 cups of Lucky Charms or 6 cups of crispy rice cereal.
Mini marshmallows melt the quickest, but any shape of marshmallow can be used
Wet your fingers to smooth out the treats in the pan.
Cookie cutters could be used to make unicorn-shaped treats - a thin layer of cereal bars is much easier to cut with a cookie cutter.