The Abyss explained: Stranger Things reveals the true nature of the Upside Down with another D&D reference

The nature of the Upside Down has been one of the biggest mysteries of Stranger Things. Even as the characters have become pros at navigating the parallel universe, they still don’t know much about it. That changes in season 5’s Christmas Eve batch of episodes, when a trip to the Upside Down version of Hawkins Lab gives Dustin (Gaten Matarazzo) a lot more information. Like so many of the characters in the show, he explains what he learned to his friends by putting it in terms borrowed from Dungeons & Dragons.