Re: Help needed: Sadistic "April Fool's" Jokes
My first reaction is for Harlequin to poke fun at accepted reality. He's nutz so making others question the world and their place in it would be a kick for him. Institutions, social conventions, and civility are the foundations for society so they will be turned on their heads.
Religion: A very respectable leader of the religious community declares a campaign to "revitalize the church". Think Buddy Jesus from the movie Dogma but with a darker twist. The brainwashed clergyman is convinced that he has received a new revelation from above and his town needs to be prepared to be ground zero of Armageddon (that happens April 1st of course!). The guy is such a good speaker he riles up half the city and the other half reacts with a violent backlash. It’s not the second coming but it might as well be...
Class: Disrupt the stock exchange (or banks of the city for something more local) so that the rich loose their shirts and the poor are forgiven their debts from loss of records. This could also be accomplished by H. printing "Fun Money" that looks normal until 12:01 AM April First. Suddenly all the people with lots of money on hand are broke.
Education: Students are sold illicit "smart pills" that makes them into (1) mindless goons, that will follow the directions of anyone wearing bells on their head; (2) ultra-smart people that are incapable of doing anything practical while they contemplate the big questions; (3) cultists that wear makeup and costumes similar to Harlequin. (The last is a great way to spread confusion when the heroes start looking for him.)
Society: All the rich people in therapy are simultaneously advised check in to a particular sanitarium. They are coerced with drugs, hypnotism, etc. to comply. Simultaneously, everyone in the local Home of the Criminally Insane are released and told who they "really are" -- all those rich people that just disappeared. Maybe while the crazies were locked up they were treated to some free plastic surgery and psychotherapy to help them assume their roles more thoroughly.
Age: the quiet communities of retirement homes are given something that peps them up (like in the movie Cocoon). Meanwhile, all the students of local schools are given downers in their school lunches and become apathetic and lethargic.
Morality: people get punished for their guilty pleasures. Basically, rip the synopsis from the movie Seven. A "lady's man" gets gang raped by militant women, a preacher is exposed for excessive (fill in your own sin), a peacenik killed in self defense when he goes on a violent rampage, etc. Irony.
Reality: The water is doped and make things look...odd. At the very least, when the April 1st release of this drug hits the city it will cause a lot of accidents and general mayhem as people try to cope with hallucinations (ala Batman: the Beginning).
Preservation: People are given a death-trap choice of doing something against their nature or dying. (ala Fight Club, Liar Liar, and a million other plots). A small bomb implanted in skulls of a doctor’s family will detonate unless all of his patients die on April 1st, etc.
I hope some of this helps.