Mack is Mack Sennett, the early Hollywood director famous for the Keystone Cops. Mabel is Mabel Normand, a waitress from Flatbush who rises to stardom in Sennett’s two-reelers. Premiered in 1974, Mack and Mabel boasted Robert Preston and Bernadette Peters in the leads, had great songs, and was nominated for eight Tony Awards. It didn’t win any and it didn’t run. Encores! gives the show another chance. —L.J.