Preheat oven to 350°. In a Dutch oven, cook beef over medium heat 10-12 minutes or until no longer pink, breaking into crumbles; drain.
Set aside 16 carrot pieces for eyes; add remaining frozen peas and carrots to pan. Stir in gravy, corn and onion. Spoon into two greased 2-qt. baking dishes or eight greased ovenproof 2-cup baking dishes.
Place mashed potatoes in a large resealable plastic bag; cut a 2-in. hole in corner of bag. Pipe ghost-shaped potatoes onto beef mixture; add carrot pieces for eyes. Bake, uncovered, 30-35 minutes or until heated through.