This picture is a crass and obnoxious misfire from Murphy, primarily due to it's unbelievably undeserved PG-13 rating. Laced with profanity, sexual innuendo and bathroom humor, you have to wonder if anyone from the ratings board was awake when this film was screened. If they think this type of fare is appropriate for young teenagers, they must live on another planet. Of course, if it had been rated "R", perhaps my opinion would be different: Murphy is often at his funniest when he's profane & irreverant, but that's for my adult sensibilities, not for those of pre-pubescent or (just barely) post-pubescent sensibilities. Murphy should know better (and has shown better judgement with the "Dr. DoLittle" pics) than to pander this kind of junk to kids.
All that notwithstanding, Murphy again essays multiple roles (under tons of Makeup) as nearly every member of the Klump family. Murphy has already worn more makeup than Boris Karloff ever did in his whole lifetime, so he must enjoy it. Tech credits are good as Murphy appears with Murphy, Murphy and Murphy in umpteen scenes, proving that split screen has been adequately exceeded with digital replacement.
Half-witted plot has professor Klump developing a youth serum, while dealing with the personal inner demons of his "Buddy Love" personna (see first movie for more details). Klump, constantly embarrased by subliminal impulses from his "Buddy" personna, isolates & extracts the Buddy Love DNA, which later spills onto the laboratory pet dog, resulting in an incomprehensible reincarnation of Buddy in human form (but with latent doggy traits). Buddy is intent on stealing the youth formula. and a race ensues to see who can complete the deal, with several dilemmas thrown in along the way. Looks like the sreenwriters swiped a few ideas from early Star Trek episodes (see "The Enemy Within").
Never mind what happens next. Change the channel. And definitely avoid the "Uncensored Director's Cut"; it just makes a bad movie worse.