Eddie Murphy's remake of The Nutty Professor used the good professor's alter ego, Buddy Love, in much the same way that Jerry Lewis did in his brilliant original: a representation of the Id out of control that plays like an admission of the actor's off-screen sins. In the sequel, Murphy expands on his Klump family from the first film and makes them major characters. Consequently, his dark side has plenty more places to express itself, particularly through the oversexed grandmother, Sherman's aggressively impotent father, and his just plain surly uncle, as well as Buddy Love (all played by Murphy).
The movie opens with professor Sherman Klump barely holding onto his sanity as his internal Buddy Love makes him say inappropriate things. He decides to extract his mutant Buddy Love gene (a sort of genetic version of electroshock therapy), but afterward is unable to maintain his original personality and intelligence. Sherman is the most bland character of the bunch, and the audience gets stuck with his boring romance with fellow professor Janet Jackson, his struggle to be nice, and generic intrigue surrounding a Fountain of Youth formula he developed. When it's not trying too hard to be nice--heck, one character is anally raped by a giant hamster--the movie works. The moral of the story is that Sherman needs to reconnect with his inner Buddy Love.