Line a 13x9-inch baking pan and an 8- to 9-inch diameter mixing bowl with foil, extending foil over edges of pan and bowl. Butter foil; set pan and bowl aside. Melt butter in a 6-quart Dutch oven over low heat. Add marshmallows and stir until completely melted. Remove from heat. Add cereal; stir until well-coated. Divide mixture between prepared baking pan and mixing bowl and press evenly and firmly into pan and bowl.

Set cereal mixture aside to cool completely, about 1 hour. Lift cereal mixture from baking pan with edges of foil. Use a 3- to 4-inch ghost-shaped cookie cutter to cut out ghost shapes. Insert lollipop sticks into ghost shapes through the bottom of cutouts.

In a medium saucepan melt candy coating over low heat. Place ghosts on a slotted spatula and spoon candy coating over ghost shapes, turning carefully using sticks to coat both sides and letting excess candy coating drip back into the pan. Carefully place ghosts on a sheet of waxed paper. Decorate face with candies before coating sets up. Let stand until coating is completely set, about 1 hour.

Stir together frosting and a few drops green food coloring; set aside. Place coconut in a resealable plastic bag. Add a few drops of green food coloring; seal bag. Shake and knead bag lightly to tint coconut.

Lift cereal mixture from mixing bowl with edges of foil and invert onto a serving platter; remove foil. Frost with the green frosting. Sprinkle with coconut. Insert lollipop sticks with ghost shapes into frosted cereal mixture.

Note: After cutting ghost shapes out of the cereal mixture, reserve your scraps for more fun shapes. Try rolling some scraps into balls and dip balls into melted vanilla- or chocolate-flavored candy coating. Sprinkle with desired candy decorations and let set on waxed paper.