It is possible you are thinking of the 20th episode of the original series, Avatar: The Last Airbender . That episode is the Book One finale, titled " The Siege of the North, Part 2 ". If you would like a detailed look at the true finale of Korra Season 1, here is an analysis of . The Climax of Book One: Air

There is no "Episode 20" of The Legend of Korra Season 1. The first season, titled Book One: Air , consists of only .

While the episode is highly rated for its tension and the tragic conclusion of Amon and Tarrlok's brotherly bond, it has faced some criticism: Legend of Korra: A Flawed Show for A Flawed World

: The villain Amon successfully strips Korra of her ability to bend water, earth, and fire. This strikes at the core of Korra’s character; unlike Aang, who struggled with the responsibility of being the Avatar, Korra defined her entire self-worth through her bending prowess.