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 each other. Helga, however, primarily targets Arnold, humiliating him for most of the day with a "King Toot" fart machine. After she sets a tray of pudding on the back of his pants, he decides to get even with her with a gift box that shines 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.
While Arnold is walking her home, she occasionally messes up by proving that she's not blind, but she manages to cover it up. After he walks her home, Arnold returned home and told Grandpa what happen with the prank, only to learn that the prank worked as it was suppose to (with Grandpa explaining that it has a "Blinding" Flash, meaning it was suppose to make her Blind). Later he follows his grandfather's advice and asks her if she'd like to go to the April Fool's Dance held at the school. At the dance, Arnold and Helga dance, but when she went to the girls bathroom 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, Helga reveals she pranked Arnold, But Arnold reveals he found out about her prank and spins Helga right into the pool. Eugene was announced to be the king of fools, but while he was walk straight he fell in the pool to. Helga swam back up and Arnold told her the jokes on her this time because he knows she’s not blind, Helga told him he wins and ask him to help her up, but she pulls him in the pool, causing everyone to jump in as well.
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 in 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.
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