Trim a corner from one short end of each marshmallow. Attach the marshmallows, cut side down, on top of the cupcakes with a dot of frosting.
Spoon 2 tablespoons of vanilla frosting into a small resealable bag; set aside.
Tint the remaining vanilla frosting neon green with the food coloring. Spoon the neon green frosting into a resealable 2-qt. freezer bag. Snip a very small corner (1/8 in.) from bag. Pipe dots of frosting along the outer edge of the cupcake with a pipe-stop-and-pull action to create spikes of frosting. Continue piping all over the cupcakes to completely cover all but the flat side of the marshmallow. Repeat with the remaining cupcakes and frosting.
Snip a very small corner (1/16 in.) from the bag with the vanilla frosting. Pipe a dot of vanilla frosting in the center of each marshmallow and attach the chocolate-coated mint. Pipe a small line to add as the sparkle in the eye.