This is the eight article of the series. Since there are a lot of theories floating out there and I'm asked often enough what I think of them, I thought I write it down. You can then laugh about me when I am totally proven wrong by "The Winds of Winter" or something like that. Rules are as follows: you put a question about any theory or plot element (really, let's stress "theory" a bit for the sake of interesting questions) either in the comments of any theory post or by mail (email@example.com) and I will answer them in an upcoming post. And if you now ask "Stefan, isn't this a shameless rip-off of Sean T. Collin's "Ask me anything"?", I would tell you to shut up, because you are right.
Prepare for part 8. Spoilers for "A Song of Ice and Fire", obviously.
Who wrote the Pink Letter?
This is a tricky one. There are basically three possibilities flying around. The first is that it's just Ramsay, the second that it's Stannis, and the third that it's Mance Rayder. I want to discount the third theory out of hand, because it just seems too wrong to me. Mance lacks too much of the knowledge, especially Ramsay's style in his choice of words, to be the author of that thing. Most obviously, his prominent mentioning of "my Reek" doesn't make sense at all. So, the second theory is that Stannis wrote it, in a ruse to bait Jon into aiding him in his conquest of Winterfell. It might be possible that the new, ruthless Stannis did something like this, but I still have a hard time to believe he would intentionally draw something into a crime as severe as oathbreaking. He would have to take his head off later, after all. That leaves us with the author Ramsay, and two alternative possibilities. The first one is that everything in the Pink Letter is true. Stannis was defeated, Mance discovered and mutilated, Theon not found and Ramsay is pissed. Note that the sample chapter from "The Winds of Winter" Martin provided us with doesn't change the possibility since the timeline isn't clear. I still root for the second option, though: Ramsay wrote the letter, and it's partially a lie. Stannis isn't defeated, but Mance discovered. This would also explain why he asks for Reek, believing Theon made for the Watch with Arya. It leaves only the question why Ramsay would write the letter. I'd guess the letter is not only meant for Jon, but for everyone else, and inflammatory enough to provoke some reaction. Either way, it spreads one information Ramsay will be desperate to spread: that he is married to "Arya" and that she's the real deal. Insulting Jon first poisons the well for a reveal of false Arya.
Why is Melisandre into Stannis that much?
We never get explicit reasoning to why Melisandre thought Stannis would be Azor Ahai in the first place, but after her chapter in "A Dance with Dragons" - whose importance can't be overstated - it becomes clear that it's most likely the result of misreading yet another prophecy. I would guess she had visions of the Great Other beyond the Wall and saw Stannis in her visions. Most likely, the image involved him in the snow, holding Lightbringer and wearing his crown, surrounded by a Blizzard and with shadows approaching him. This could easily be the upcoming battle against Ramsay, but when you saw Evil just before, it would be easy to misread it. Stannis is a figure with distinctive features, while the Starks appear to her as wolves most of the time, so it's likely that she jumped to the conclusion based on the facts she knew. When she met Stannis, who is a rather intimidating personality, and learned of his rigid honor code, she might have seen it as additional proof. Seriously, this woman should start to make mindmaps after her visions, it might help her a great deal.
What is Lightbringer?
Lightbringer enters the story unglamourously. We are more or less informed that Stannis has a "magic sword", a fact that is played notably low in "A Clash of Kings" and gains importance only in Maester Aemon's examination in "A Storm of Swords", where our suspicions are first roused because the sword is cold. That is odd for a flaming sword, I agree. We see it later in "A Dance with Dragons", when Stannis raises it over his head in the wildling ceremony. And here it begins that the pieces fall together. Melisandre states in her chapter that she is glad Jon killed "Mance" because upholding the glamor cost her more strength than she was comfortable to admit. The explanation for this could be that Melisandre doesn't uphold one glamour, but two: Mance glamoured as Rattleshirt, and some ordinary piece of steel as Lightbringer. And that's just what "Lightbringer" is: a ruse, a cheap trick to impress other people, including, most likely, Stannis. Seeing Melisandre's rather limited skills as a reader of prophecy, it seems her skills at glamouring are what really found her power base.