Gently push 1 pretzel into 1 flat side of each marshmallow; set aside. Plan and assemble decorations for each marshmallow.
In 1-cup microwavable measuring cup, microwave 1/2 cup frosting uncovered on High 10 to 20 seconds or until smooth and melted when stirred. Add 1 to 2 drops food color as desired--green for witches or Frankenstein, red for devils, yellow for pumpkins or cats.
Dip and decorate 1 marshmallow at a time. Hold pretzel, and dip marshmallow into frosting to coat all sides. Immediately add decorations to create features--candy corn for noses, baking bits for eyes, string licorice for whiskers. To make witch’s hat, push corn snack through center of peach ring. For devil’s or witch’s cape, use fruit snack cut in half crosswise at an angle; attach at base of marshmallow while frosting is soft. Set pretzels in drinking glass to dry before storing. Store in airtight container.