The band of Demogorgon-hunting misfits in Stranger Things may echo the Losers’ Club of Derry who fought off a shapeshifting monster in a clown suit some 30 years before in Stephen King’s IT, so of course a fan theory about some link between these two deranged worlds was eventually going to emerge.
What fuels the theory even more is that Bob grew up in the late ‘50s when the thing from the Macroverse was awake, in the place where Pennywise made a lair out of the sewer system and lured unsuspecting kids into his gaping maw with balloons. Never mind the fact that Finn Wolfhard stars in both Stranger Things and the movie version of IT. Neither of these glaring similarities can canonically link the two universes, but while the theory officially remains inconclusive, there is a way it could actually work in the collective fandom imagination.
Anyone who’s read enough Stephen King to induce insomnia has probably been subjected to the Macroverse at some point. This alternate reality also known as Todash Darkness is a sort of Upside-Down where menacing darkness surrounds everything that you would otherwise recognize in the right-side-up world, so inspiration for the Duffer Brothers (who are both admittedly terrified of clowns) was lurking in there.
“Tim Curry’s performance as Pennywise really messed me up,” Matt Duffer told Vulture of the duo’s coulrophobic tendencies. “Like, it scarred me in a major way. It was one of the first true horror things I had seen, and I had not experienced Stephen King before. That was my first experience with Stephen King, so that was a really huge point in my life. It was two weeks, at least, of no sleep because of that,” he recalled.
Creeping back to the fan theory, it floats more when you consider that the Upside-Down might just be another tentacle of the Macroverse reaching far beyond Derry to send another sleepy suburban town into unexpected chaos. Like the Upside-Down, the Macroverse is infested with monsters that are not just shadowplay. If these things don’t have teeth, then they have claws or knives or may just take you captive and drag you to their evil overlord—which goes into a whole other theory about how IT is really the Red King, but that would effectively kill several pages.
The point is that you could make a convincing argument by turning that clown upside-down, but there is no intended connection between the two worlds.
“I think [Bob’s clown story] was really me describing something that just freaked me out,” Duffer added. “I didn’t have that experience myself. I just had nightmares like that.”