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In the first episode, Naruto failed the Graduation Test because he couldn't create a proper clone. Mizuki falsely tells Naruto that if he learns a Jutsu from the Forbidden Scroll, he can graduate. As such, Naruto studies, and successfully performs the Shadow Clone Jutsu, with Iruka commenting how Naruto was able to master an advance Jutsu with so many clones.
But what makes the Shadow Clone Jutsu more advanced than the Clone Jutsu that Naruto failed at?