In a large saucepan, melt the butter over low heat. Add the mini marshmallows and stir continuously until fully melted and smooth. Remove from heat.
Stir in the green food coloring and vanilla extract, mixing until evenly combined and bright green.
Gently fold in the cornflakes, coating them completely with the green marshmallow mixture.
Spray your hands with nonstick spray or lightly butter them. Scoop small portions of the mixture and shape them into round wreaths on a parchment-lined baking sheet. While still warm, press 2–3 red candies onto each wreath for decoration. Allow to set at room temperature.