Fool's Day Out is the twenty-first episode of Season 2.
Tired of being pranked by everyone (His parents, Cosmo, Wanda, his friends, and the rest of the citizens of Dimmsdale), Timmy summons the April Fool, the ultimate prankster. But, unknowingly to Timmy, once the April Fool starts, he doesn't know when to stop. Timmy must stop him before he destroys the Earth completely.
It's 4th of July and Timmy gets a hat by his parents, but a pie comes out of it and hits him in the face. Days later, it's Halloween and he gets a pumpkin by Cosmo and Wanda, but another pie hits him in the face. Later, it's February 2nd, Chester and A.J. give him a Marmot who attacks him if he sees his shadow.
Tired of being fooled, Timmy chooses April Fools' Day to take vengeance on everyone who made him jokes by calling The April Fool to help him make jokes in school. And the ultimate prankster called the April Fool to gave them pranksters in April. But he destroys the earth later... and non stop laughter come for the prankster. but he completes his celebration who s' funny with the fairies pranked Timmy.