Netflix has just unveiled an electrifying new trailer for the fifth season of Stranger Things, set to premiere in less than a month.

The final chapter of Netflix's wildly popular supernatural drama is slated to be released in three parts throughout November and December.

As one of the most eagerly awaited streaming events of 2025, fans are buzzing with speculation about what lies ahead for Eleven (portrayed by Millie Bobby Brown), Will Byers (Noah Schnapp) and the rest of the Hawkins crew.

With the young heroes preparing for their final showdown against the formidable Vecna (Jamie Campbell Bower), some sharp-eyed viewers believe there's an even bigger threat lurking.

A comprehensive theory was shared on Reddit shortly after the conclusion of the fourth season in 2022, reports the Mirror.

The user posited: "Season Five's Villain is the Thessalhydra and it's been set up since Season 1."

Like many of the beasts encountered by the Hawkins group in Stranger Things, the Thessalhydra originates from Dungeons and Dragons.

This enormous creature, boasting a gaping maw and multiple heads, has been hinted at several times throughout the series, including during the team's initial venture into the Upside Down in the fourth season.

"In one of the later episodes of season 4, Nancy (Natalia Dyer), Steve (Joe Keery), and Robin (Maya Hawke) are all running around in the Upside Down when they hear a loud, terrifying, terrible sound," the theory suggests.

"They wonder what the heck it was and if it caused an earthquake or something, but the subtitles even say that it is a creature roaring off-screen.

"But the three of them are very busy doing Very Important Vecna Things, so they disregard the other random terrifying creature and press on."

Eleven and her companions have already defeated one enormous entity from the Upside Down, the massive, spider-like Mind Flayer at the conclusion of series three.

Yet, this persuasive theory implies there's another formidable beast that requires eliminating before Hawkins is safe; either an intelligent entity that's been covertly orchestrating events or a hideous subordinate being controlled by Vecna.

The latest trailer for Stranger Things series five is remaining tight-lipped for the time being, though one fleeting moment could support the widespread fan theory.

Some sharp-eyed watchers have noticed that, upon closer inspection, a Thessalhydra figurine appears on a table when Mike assembles his allies to "end this once and for all".

Might this be a clue that the group are plotting an assault on another previously hidden danger from the Upside Down?

Stranger Things season 5 part 1 will be released Wednesday, 26th November on Netflix followed by part 2 on 25th December and the final episode on 31st December.