WARNING: The following contains spoilers for Attack on Titan.

With the recent conclusion of Attack on Titan's third season came the news that its follow-up, due to air in 2020, will be the show's last. Considering how many long-held secrets Season 3 unlocked about the hidden nature of Titans and the truth about Eren Jaeger's world -- and knowing that creator Hajime Isayama's source material has already wrapped up -- it shouldn't come as too much of a surprise that the end is now in sight.

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For all that Season 3 revealed, there are still more than a few burning questions and unresolved plot points for the show to address, all of which we hope will be satisfyingly done in the fourth and final season.

Thanks to Grisha Jaeger's basement diaries, we now know the truth about the Titans' origins: 2,000 years ago, Ymir Fritz made a deal with the "devil" -- depending on who you ask -- imbuing her with the power to transform into the First Titan. Her progeny became known as the Subjects of Ymir, and when she died 13 years later (the average lifespan of a Titan of her kind), her powers were divided among nine individuals and passed down from generation to generation.

In the anime, these special Titans are as follows: The Founding Titan (now possessed by Eren); the Attack Titan (also with Eren); the Colossal Titan (now possessed by Armin); the Beast Titan (possessed by Zeke, Eren's half-brother); the Armored Titan (possessed by Reiner, who is on the run with Zeke); the Cart Titan (Zeke's getaway vehicle); the Female Titan (Annie, still, we presume, imprisoned by the Scouts); and Ymir's Titan, still without an official name.

But that only leaves us with eight. The manga, which we won't be relying on much for insight here in order to avoid spoilers, features two Titans we haven't seen yet: The Jaw Titan and War Hammer Titan. But, given the differences between the anime and manga versions of the nine Titans, we can't automatically assume that either of these two will turn out to be our missing ninth.

Ymir revealed herself as a Titan midway through Season 2 in order to save her love interest, Historia -- the secret heir to the throne -- and the rest of their Scout unit from a Titan attack.

Through flashbacks we slowly learned that, 60 years ago, Ymir was a homeless girl who was transformed into a Titan by a shadowy cult that worshiped her as "goddess." They gave her her name, which we now know refers to the Eldian's progenitor, meaning it's possible this group were, like Grisha, from beyond the Walls. After their activities were broken up by soldiers, Ymir spent decades in hibernation, eventually stirring when she sensed the presence of the Warriors (Reiner, Bertholdt, Annie and their friend, Marcel.) At the end of Season 2, she aided Reiner and Bertholdt in their mission to kidnap Eren, using it as an opportunity to elope with Historia.

She was eventually forced to give up on her grand romantic gesture and agreed to go with Reiner and Bertholdt back to the Marleyeans so they wouldn't return empty-handed. The only time we hear from her in Season 3 is through a letter sent to Historia that suggests she might be dead, and her Titan power has been passed on to another.

It would be real shame if this turns out to be true. Ymir was one of the series' most complicated and interesting figures and an off-screen death just isn't worthy of her character. The mystery face we see behind bars in the Season 4 teaser certainly bears a strong resemblance to her, giving us hope for Ymir's return.

In the closing moments of Season 3, a world-weary Eren pointed a finger across the newly discovered ocean and asked his fellow Scouts if there were people that wanted them all dead beyond the horizon.

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The answer, as know from flashbacks of Grisha's oppressive life in the Marleyean Empire, is yes. The Marleyeans harbour both a historical hatred of the Eldians, who once ruled over humanity with a Titan-powered, iron fist, and a greed for the rich oil deposits that lie under Paradise Island -- Eren's home.

They're the source of the steady stream of Titan attacks, and the ones who coordinated the Beast Titan and Warriors' mission. Naturally, Zeke and Reiner would have relayed the details of this failed mission to their superiors and will likely put another plan into motion. It's also likely that the Scouts and the rest of Paradise Island's military will switch to the offensive and take the fight to their hidden human enemy for the first time, evidenced by the alterations made to their omni-directional gear in the Season 4 teaser.

One of the weirdest new Titan powers Season 3 unveiled was the ability for hosts of the nine Titans to glimpse memories of a future host. Eren Kruger hinted at this when he mentioned the names of Mikasa and Armin before passing on the Attack Titan to Grisha Jaeger.

It's strange that Kruger would see Eren Jaeger's future and not Grisha's considering he was the direct inheritor. This generational skip could confirm just how important Attack On Titan's primary hero is to the Subjects of Ymir; that Grisha was merely the conduit to ensure the Attack and Founding Titan powers were passed on to the person destined to lead the Eldians to freedom.

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Beyond this, there could even be some kind of cyclical history at play -- a favored storytelling conceit for sci-fi tales. The cosmic image of every Titan stream leading to and from their source (Ymir Fritz) and repeating episode titles could, at a glance, support this. Following this idea further, we could also reassess the title of the very first episode: "To You, In 2,000 Years - The Fall Of Shiganshina." Could we have a Battlestar Galactica situation on our hands with Attack On Titan Season 4?

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