At first, Biff was the skinniest mouse in his class. He then decided to become strong and work out. He forced the mice to work out and made them lift cheese barbells, much to their chagrin. He goes hard on them when they do so. He also is Emily's boyfriend, since she thought he was cute. He even forced Garfield to work out, much to his dismay. When he feels sad, he stops being strong and eats junk food like Garfield, as shown in 'Fitness Crazed'