April Fool's Day is a special half-hour episode in the Hey Arnold! TV Series.
It's April Fools Day and Helga has targeted Arnold as her practical joke victim for the day. When Helga goes one prank too far, Arnold stages a retaliation and brings in Grandpa's prized practical joke.
It's April Fool's Day at P.S. 118 and everyone is playing pranks on one another. Helga, however, primarily targets Arnold, humiliating him for most of the day. After she sets a tray of pudding on his seat, he decides to get back at her with a gift box that glares a bright light, claiming it's a belated birthday present. Unfortunately, he isn't aware that the box temporarily blinds someone. Helga decides to use this to her advantage by acting like she's permanently blind to indirectly force Arnold to be her personal slave. She occasionally messes up by proving that she's not blind, but she manages to cover it up.
After he walks her home, he follows his grandfather's advice and asks her if she'd like to the April Fool's Dance held at the school. She reveals to Phoebe that she's pretending to be blind only to reveal to Arnold that it's another prank, but Gerald overhears this and tells Arnold. They come up with a plan to finally get back at Helga without hurting her this time. Arnold and Helga dance while Gerald opens up the pool that's in the gym. Right before the King of Fools is announced, Arnold spins Helga right into the pool.
This episode was produced in 2001, when Nickelodeon ordered an additional three half-hours for Season 5 after deciding to release the TV movie Arnold Saves the Neighborhood on theaters as Hey Arnold! The Movie.
As a result of being produced one year after the rest of Season 5 and the movie, this episode features Alex D. Linz as the voice of Arnold and Taylor Gifaldi as the voice of Sid since their previous actors went through voice changes during the one-year production hiatus as they were going through puberty.
According to Craig Bartlett, this episode is meant to take place after the events of Hey Arnold! The Movie, and was written from the perspective that Arnold has already heard Helga's confession, and is aware of her feelings for him.