Melt butter over low heat until completely melted. Gradually add marshmallows and stir often to avoid burning them.
When marshmallow/butter mixture is completely melted, add 1/2 teaspoon of vanilla and your green food coloring and mix well. Remove from heat and stir in your Rice Krispie cereal.
Once mixture is mostly combined, stir in the Lucky Charm’s marshmallows. My kids and I picked them out of the Lucky Charms. If possible, store in an air tight container and they will stay softer longer! A ziplock bag works great!