The Joker employs a harmless, if not still dangerous, mind altering laughing gas mixed with Ivy's spores to transform the citizens of Gotham into laughing fools, all on April Fools Day. This is an attempt to lure out heroes into the open and use the city as leverage to gain Chaos Emeralds as a prize for Bowser's schemes.

If Batman and The Emerald Searchers don't stop the Joker in time, everyone will soon go totally mad, including Alfred, Chris, and Sailor Mini Moon.