Although he was eventually rescued and returned to normal life, his time in the Upside Down left him with a mysterious connection to the alternate realm. A year later, Will became possessed by the Mind Flayer, becoming a part of his hive mind.

Is Will Byers a Demogorgon?

Perhaps that plan is transform him into the Demogorgon; however, by the end of Season 2, Will has been "exorcised" of the evil of the Upside Down, meaning that this universe's Will may no longer become a Demogorgon. In Season 3, instead of Will becoming a Demogorgon, the Mind Flayer turns its sights on Billy.

What is wrong with Joyce Byers?

Joyce has anxiety problems, which are pointed out by both her older son and ex-husband.