its a cartoon caalled the nutty proffessor

When beautiful Carla Purty joins the university faculty, genetic professor Dr. Sherman Klump grows desperate to whittle his 400-pound frame down to size and win her heart. So, with one swig of his experimental fat-reducing serum, Sherman becomes 'Buddy Love', a fast-talking, pumped-up, plumped down Don Juan.

To impress a beautiful girl, Harold Kelp, the grandson of professor Julius Kelp, who created a potion to transform his personality, gets his hands on his grandfather's secret elixir and unleashes his destructive alter ego, Jack.