The most straightforward theory is the one that makes the most sense, especially if the Duffers continue to split the party into groups. Vecna/Henry/One is Eleven’s nemesis and has been searching for her since she escaped the lab. Will was the Mind Flayer’s first victim to enter the Upside Down, so each battling their own demon in a two-pronged attack makes the most sense.

There will probably be multiple parties; however, it’s pretty easy to imagine the final battle comes down to Team Eleven going after Vecna while Team Will tackling the Mind Flayer.

There’s been debate over the painting Will made for Mike and his speech about it in Volume 2. The most obvious is that Will is giving a sideways confession of his feelings for Mike without directly outing himself, which Mike completely misses. (Jonathan does not miss the subtext in his brother’s monologue, as seen in his knowing look in the rearview mirror.)

But viewers also noticed the changes in the painting from the original D&D campaign from Season 1, with Mike as a knight instead of the DM and the party battling a three-headed dragon, which was not their target back then. There is a theory that Will has (perhaps without even being aware of it) painted an image of the future and the series’ final battle. Nancy said Vecna’s visions showed a massive monster still to come, which fans theorize could be Tiamat, the mother of all evil dragons. Each person in the party will be needed for their skillset, with Mike leading the charge.

One dire prediction focuses on Will’s unrequited feelings for Mike as his weak point. Several theories suggest Vecna could straight-up possess Will the way the Mind Flayer once did, but that seems a bit too close to a rerun of Season 2. A more nuanced take is for Will to side with Vecna of his own volition.

Stranger Things 4 showed Vecna preys on bad thoughts, self-hatred, and guilt. Will already has trauma from Seasons 1 and 2, he’s in love with his BFF who doesn’t even notice, and he is forced to watch Mike be in love with a girl who is more powerful than he could ever be. It would be very easy for Vecna to get inside Will’s head, stir up all that jealousy Will pretends he doesn’t feel, and offer him to be Eleven’s equal and punish Mike and Eleven for hurting him.

The counter-argument to the above theory is that if Will can be turned to Vecna’s “dark side,” love can bring him back. Will’s speech to Mike about being “the heart” may have been foreshadowing, but not for the monster the group with defeat. It could actually be telling Mike the secret to defeating Vecna.

Eleven already experienced this in the Stranger Things 4 finale. Love can conquer all, even bringing back Max from beyond the grave. Mike begging Will to return to them and telling Will he’s loved could be the “heart” Will was talking about.

There’s also a theory going around that Will and Vecna’s link isn’t an accident, that instead the two of them are counterparts on each side of their universe. It’s a bit complicated, but TikTok user @bunkyyy, posited an interesting idea, using the famous “Good vs Evil” alignment chart from D&D.

Vecna is “Neutral Evil.” He’s not lawful or chaotic; he’s just straightforward evil. In the bonus companion Stranger Things: Worlds Turned Upside Down, Will’s D&D profile confirms he is True Neutral, and a magic user, like Vecna. That puts him directly in a line with Vecna on the chart and would explain why the Upside Down chose Will in the first place. It also explains their connection.

If Will and Vecna are connected, what does that mean if the kids are to ultimately take Vecna down? More than a few viewers have started to recall how Harry Potter versus Voldemort went down. In that case, Harry was the horcrux keeping Voldemort alive and had to sacrifice himself. Some theories go as far as to suggest a piece of Vecna is in Will. Even if you don’t buy that part, it still seems a likely possibility Eleven ending Vecna once and for all may require Will’s ultimate sacrifice.

Finally, in the “don’t ever count out the answer being far more off the wall than anyone could guess,” there’s the theory that this is all in Will’s head. It’s based on the odd plot hole viewers noticed that the Upside Down isn’t frozen in time from when Eleven originally opened it, but rather the night Will first entered.

The theory posits the Upside Down is a mental projection of Will’s real-life D&D campaign, which Will may not realize. Hawkins’ permanent frozen-in-time place is from the moment when he was happiest. The theory suggests Will is going to re-enter the Upside Down and discover his powers to control and manipulate it. He would then be the ultimate weapon against Vecna.