Crystal Scales. Actress: Jimmy Neutron: Der mutige Erfinder. Crystal Scales is an African-American actress, rapper and singer who is mostly known for voicing Libby Folfax from the Jimmy Neutron: Boy Genius franchise by Nickelodeon. She also voiced in other animated works and video games such as Titan A.E., Batman: Gotham Knight, Psychonauts, Scooby-Doo, The Boondocks, Class of 3000 and Tutenstein.