Robin Reckoning: Part I is the introduction of one of the show's best two-parters. The origin of Dick Grayson as Robin; the death of his innocence and parents. The two-parter is simply put wonderfully done from the acting, the story and the direction making the animation sing the tragic origin story of one Batman's greatest supporting characters: Robin.
What's not to like here? We have Batman's sidekick wanting vengeance for his parents' death, a similar rage that drives Batman's conquest against crime, but Robin is still younger than The Dark Knight and more susceptible to moral corruption than Bruce Wayne is. This two-part episode dives right into the relationship between Bruce and Dick, and shows the father-son dynamic between the two: this makes it one of the most captivating and investing episodes of Batman: T.A.S.
If you haven't seen the animated series in its entirety, just do it right away. It's 2017, the 25th Anniversary of the classic show, so get watching asap!