The filmmakers thought we might be able to identify with them on this level, but the only thing that happens is that they become not funny. Sherman decides to extract Buddy Love, his alter ego from the first film, from his brain, accidentally bringing him to life. Meanwhile, Sherman keeps losing his intelligence and must get Buddy back before he gets really dumb. If he doesn't, he'll become dumb enough to actually enjoy this movie. Every joke in this movie is telegraphed way in advance.
Every joke is given away full minutes before they actually happen.
For example, Sherman's formula makes a hamster grow to 8 feet tall. Someone hides under a fur coat and tries to crawl away from it. This movie tops itself in putting multiple Eddie Murphys on screen at the same time. An early scene in a restaurant features five Eddies, plus Janet Jackson and countless extras in the background. One single shot has Jackson accompanied by Mama Klump to the table, where she then sits down next to Sherman, interacting with both of them in the same shot.