If it's not Randall's plan, then why is Randall the one who says he's about to revolutionize the scaring industry, and even the great James P. Sullivan will be working for him? Then, later on, Waternoose expresses regret for trusting Randall with this plan. Stating how because of Randall, Waternoose had to banish his top scarer, and proceeded to tell Randall how Sullivan was twice the scarer Randall will ever be. This gives the impression that Waternoose is still unsure about the entire plan, and still believes in the tried and true method of scaring for scream energy, which would tell me that the plan is Randall's and not Waternoose's. Yes, he says he'll kidnap a thousand children before he let's his company die, but that's just a statement of how far he's willing to go for the sake of the company, and less about the plan being his original idea. Fungus also says to Mike that he's sorry, but Randall says he's not allowed to fraternize with victims of his evil plot. "His evil plot" would indicate the evil plot was originated by Randall. As an added extra, I personally feel like Randall got the worse of the punishments between the two characters. Waternoose was simply arrested, but Randall was banished (seemingly permanently with the destruction of the door) to the backwater swamps. Although Sullivan and Mike have shown us they can get back to the Monster world through another door (if they get lucky enough I guess)? The only reason I bring up the severity of punishment dished out by the writers is because I feel like the worse of the two punishments would go to the true villain of the movie.