Stranger Things: The Game is a loose, retro retelling of the first season, but dedicated players have found that it also contains a new scene from Stranger Things season 2. Reddit user icecreamboy201 says the video is only accessible roll after you beat the game.
Minor spoiler warning: It doesn't seem like any major plot points are addressed in this scene, though you do briefly see a new character. Treat it like any other trailer if you'd rather come into the series totally fresh.
The scene shows the four boys out trick-or-treating on Halloween as the Ghostbusters, complete with matching jumpsuits and proton packs (also, for some reason Will is toting around a "compact" video camera and filming the whole thing). With their costumes sadly unrecognized but their candy demands met, the kids bicker about the relative quality of Three Musketeers bars until somebody in a Michael Myers mask jumps out and scares the khaki out of them. No, this isn't a Halloween crossover - it's just Max, one of the new characters joining Stranger Things for its second season. She pulls off the mask and mocks their terrified reactions, then the scene ends.
One time late in my trick-or-treating career I literally just put on a leather jacket and sunglasses and went as, I don't know, a rebel or something? They weren't even '50s-looking sunglasses. So these kids definitely have me beat with their matching Ghostbusters cosplay, even if none of the plebe adults handing out candy realize their greatness.