(CNN) -- It's the Mother of All Battles.
For diehard fans, every new "Game of Thrones" episode is appointment viewing, but Sunday night's show has anticipation at an all-time fever pitch.
The show's creators have said almost the entire episode will be devoted to an epic clash between a patchwork band of its human heroes, holed up in the northern castle of Winterfell, and an army of undead warriors led by the inscrutable Night King.
The Battle of Winterfell is the climactic showdown the entire HBO series has been pointing to since Season One way back in 2011.
Here's why everyone is so jacked up for it.
It's reportedly the longest battle sequence ever put on film
The first two episodes this season were each under an hour, with minimal bloodshed. This one is around 80 minutes -- pretty much all of it wall-to-wall combat.
The "Game of Thrones" producers believe it's the longest consecutive battle sequence ever committed to film.
Director Miguel Sapochnik told Entertainment Weekly he tried and failed to find a longer battle scene in a movie. The closest was the 40-minute siege of Helm's Deep in 2002's "The Lord of the Rings: The Two Towers," which has long been a gold standard for epic cinematic battles.
The choice of Sapochnik as director also has heightened expectations. He shot "Hardhome" and "Battle of the Bastards" -- arguably the two most intense and acclaimed action sequences the show has done til now.
The episode required 11 weeks of night shoots in Northern Ireland, where much of "Thrones" is filmed.
"What we have asked the production team and crew to do this year truly has never been done in television or in a movie," co-executive producer Bryan Cogman told EW. "This final face-off between the Army of the Dead and the army of the living is completely unprecedented and relentless and a mixture of genres even within the battle. There are sequences built within sequences built within sequences," he added.
"It's been exhausting but I think it will blow everybody away."
- Some favorite characters will die
Unless you were really attached to little Ned Umber, nobody of consequence has died so far in this final season.
That's about to change.
Some two dozen key characters are in harm's way at Winterfell, and it seems highly unlikely that all of them will survive. So who's in the most jeopardy?
Speculation has focused on characters whose story arcs have stalled or reached some sort of closure, making them expendable.
It realigns the chessboard for the series' endgame
Three episodes remain after the Battle of Winterfell. The fact that this battle comes now -- and not, say, during the final or penultimate episode -- is hugely significant.
We can assume the White Walkers don't wipe out everybody in the north, because nobody wants a Night King vs. Cersei finale.
So, as we suspected all along, the show's ultimate clash is likely not with the Army of the Dead. It's between the ambitious humans of Westeros over who -- if anyone -- will sit on the Iron Throne at the end.
Yes, whoever survives will have to deal with Cersei, who is sipping wine and amassing her army-for-hire in the south. And assuming they're both alive, Jon Snow and his queen/lover/aunt/rival Daenerys have some unfinished business as well.
Then there's a popular fan theory going around that the Night King isn't even at Winterfell -- that he's split his massive army in two and is heading for King's Landing with his zombie dragon, where a million unsuspecting city dwellers are waiting to be turned into wights.
Based on their past staredowns beyond the Wall, it feels inevitable that Jon Snow and the Night King are heading towards a climactic, one-on-one duel to the death. But for "Game of Thrones," which has thrived on confounding expectations, that might be too predictable.
One thing is sure: After Sunday, Westeros will never be the same.
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