At the end of “Chapter 2: Trick or Treat, Freak,” Dustin (Gaten Matarazzo) made an interesting discovery in his trash can. When “Chapter 3: The Pollywog” begins, Dustin’s new pet resembles the slimy blob Will (Noah Schnapp) threw up in season one. When Dustin feeds the little creature some of his “Three Musketeers” Halloween candy and nicknames it “D'Artagnan…Dart for short,” I was immediately reminded of the movie Gremlins.