Place popped popcorn in a large bowl and set aside.
In a microwave safe bowl, melt marshmallows and butter on HIGH for 1 to 2 minutes, stirring half way through, until mixture is smooth. Pour over popcorn and stir well until coated and sticky. Mold popcorn into 8 balls and place on wax paper. Cut fruit leather into 24 1-inch triangles (for eyes and nose) and 8 jagged squiggles (for mouths). Apply fruit face pieces to popcorn balls. Serve as is or wrap in plastic to save for later.