With the final season of “Stranger Things” generating increased interest in “Stranger Things: The First Shadow,” the Broadway production has extended its run through September 6.

Based on an original story by “Stranger Things” creators the Duffer Brothers, Jack Thorne (Harry Potter and the Cursed Child), and Kate Trefry (“Stranger Things”), the prequel play tells Vecna’s origin story and features younger versions of several of the series’ characters.

In 1959 Hawkins, Indiana, the Creel family seeks a fresh start, especially their teenage son Henry, who is eager to escape his...