The Case of the Stuttering Pig (1937)

One dark and stormy night, Porky, Petunia and their brothers learn from Lawyer Goodwill that they inherit a fortune from their late Uncle Solomon. But if something happens to the siblings, the fortune goes to the lawyer who assures them that nothing does and then adjourns to the basement. He walks into a secret laboratory, drinks a bottle of Jekyll and Hyde potion, and turns into a hideous monster. After he warns the audience that they cannot stop him, he has everyone except Porky and Petunia, but that guy in the third row exacts revenge and means business.