1. Roose Bolton is an undead creature who steals faces and nails them onto his own.
This theory, referred to as “Bolt-ON” (get it, he bolts them on) is only sort of a joke. The Bolton family preference for removing people’s skin is oddly specific, and lots of emphasis in the books in placed on how Roose Bolton never seems to age.
An extra-scary version of the Bolt-on theory says that Roose is keeping Ramsay around solely to harvest his skin.
2. Syrio Forel is Jaqen H’ghar
According to this theory, the Faceless Men have been keeping an eye on Arya Stark since long before she left King’s Landing. Syrio’s death is never explicitly depicted in the books or the show, and seeing as he is from Braavos it’s possible he has a connection to the House of Black and White.
Jaqen already seems familiar with Arya when they meet, which implies that he already knew who she was before she freed him from the burning carriage.
3. Bran accidentally cannibalized Jojen Reed.
While hanging out north of the Wall in that giant weirwood, Bran is fed a paste made up allegedly of weirwood seeds. There is something red floating in the broth, and Bran worries that it looks a lot like blood. This theory states that it IS blood, specifically the blood of Jojen Reed, who is increasingly weakened by his stay in the tree and disappears from the text after Bran drinks the paste.
4. The Hound is alive and is going to THROW DOWN with his undead brother.
This theory states that the Hound, Sandor Clegane, did not die of his wounds (in both the show and the books, Arya refuses to euthanize him). He survived and has been in hiding ever since his “death.”
Concurrently, the Mountain, Gregor Clegane, DID die when Oberyn Martell poisoned his blade in their battle for Tyrion’s freedom but was brought back to life by Qyburn, who put the new Frankenstein’s Mountain on the Kingsguard.
Now that Cersei requires a trial for her crimes against the Faith, she will call upon the undead Gregor to be her champion, and the Faith of the Seven will call for a champion of their own; Sandor Clegane will jump at the chance to finally face his hated elder brother in an amazing, badass bro-on-bro CLEGANEBOWL. Get hype!
5. Tyrion Lannister’s first wife is alive and living in Braavos as a prostitute. Oh, and he may have a daughter.
Tyrion’s first wife was a woman named Tysha who was cruelly driven from Casterly Rock by Tywin. Tyrion never saw her again, but a background character from later books describes a prostitute in Braavos who makes all of her clients marry her before sleeping with them.
This woman, called the Sailor’s Wife, is theorized to be Tysha because her tradition of marrying her customers mirrors the torment Tywin put her through. When he discovered his son had married her, Tywin told his guards to gang-rape her and pay her each time, to show Tyrion what happens when Lannisters marry “lowborn whores.”
Most importantly, the Sailor’s Wife has a golden-haired daughter named Lanna (perhaps short for Lannister?) who is 14 years old. According to the theory, she is Tyrion’s daughter and was conceived during their brief marriage.
6. Cersei accidentally killed Joffrey by trying to poison Tyrion.
Now, we know everyone thinks that Olenna and Littlefinger killed Joffrey with wine, but this theory reminds us that Joffrey (in the books at least) stole a bite of Tyrion’s untouched pie and ate it right before dying. He even exclaims “it’s the pie” as his last words.
This theory says that Cersei had planned to poison Tyrion with the pie at the wedding, and when Joffrey ate the poison instead, she lashed out and accused Tyrion of the murder.
As for Olenna, Littlefinger gave her a false poison so she would THINK she killed Joffrey, to bind himself to the Tyrells with a deadly secret and, in one fell swoop, drive Sansa straight into his waiting arms. It’s a stretch, but hey — all theories are.
7. Most Northern houses are secretly still in rebellion and want to crown Jon Snow as King in the North.
This amazing theory, often called the Grand Northern Conspiracy, is HUGE in scope and should be read in its entirety on the author’s Tumblr. It hedges in part on a passage in the books where Robb Stark states in a private conversation that if he were to die, he would want Winterfell to pass over Sansa (who was married at the time to Tyrion) and instead fall to Jon.
Further conversations insinuate that at LEAST House Manderly and House Mormont are in on this, and they have been subtly sabotaging the Boltons’ grip on the North in the months since Robb’s death.
8. Even before Robert’s Rebellion, civil war was brewing in Westeros.
The Southron Ambitions theory adds an entirely new layer to the forces that shaped Westeros as we read and watch it. It states that the Starks, Tullys, and Arryns banded together in marriage and fostering because Ned Stark’s father’s generation intended to forge an alliance strong enough to depose or assassinate the Mad King Aerys.
This explains why these three houses are so connected, as Stark children are sent to foster under Arryn eyes and Tully daughters marry Stark and Arryn heirs (at the expense of better matches, seeing as Lysa Tully was supposed to marry Jamie Lannister before marrying Jon Arryn).
Then of course their ambitions fell into a flaming pile of shit, but if the theory is true, then the war in Westeros has been going on for at least 30 years longer than we thought.
9. Melisandre is super old and looks nothing like what we think she does, and also may be a zombie.
There are plenty of theories about the mysterious Melisandre, but a prominent one suggests that she is sneakier, and older, and uglier, and less alive than she lets on. She is known for being great at glamour spells and wears a glowing red jewel that never leaves her throat — is it a power source to maintain her youthful and beautiful appearance? What does she actually look like?
Further theories say that she never gets cold on the Wall, which suggests that she may not even be alive to begin with.