In a large bowl, mix together the Rice Krispie cereal and Lucky charms marshmallows.
In a large saucepan over medium heat, melt the butter.
Add the 8 cups of mini marshmallows and salt and stir into the melted butter. Continue stirring over medium heat until the marshmallows are completely melted into the butter.
Pour the melted butter and marshmallow mixture over the Krispie cereal and Lucky Charms marshmallow mixture and gently stir with a rubber spatula until evenly combined.
Spread the Krispie mixture into a 9-inch square pan and press gently with the spatula to flatten the top.
Allow the St. Patrick's Day Krispie Treats to cool in the pan for about 30 minutes before slicing and serving.