Place popcorn in a large bowl; set aside.
Melt butter over medium heat in a medium saucepan. Stir marshmallows into butter until melted. Stir in gelatin powder until evenly colored. Pour over popcorn and stir until evenly coated. With buttered hands, shape popcorn into 7 oval shapes.
Flatten one oval shape slightly and squeeze one end to form a ‘skull’ shape. Place onto parchment lined baking sheet. Repeat with remaining shapes.
To decorate: Press two gumballs into each skull to form ‘eyes’. Press candy corn into skull to from ‘teeth’. Use scissors to trim candy strips and press into top for ‘hair’. Sprinkle with sugar sprinkles.
Allow ‘zombies’ to set for about 20 minutes before wrapping individually in plastic wrap (or serve immediately).