I believe the text supports Mance writing the pink letter.  Here I will discuss the evidence. I do not claim to know Mance’s motivations or all the details. I believe at this point GRRM has not given us enough info to know everything.   Let’s start by discussing why it is not Ramsay. 1)   No seal, only a smear of wax, no skin, no evidence it’s written in blood 2)   Threats in letter do not match his MO, e.g. heads on spikes 3)   Language used in the letter is not consistent to any one person, suggesting whomever wrote it was intentionally trying to sound like Ramsay 4)   Jon is now coming to WF with an army of wildlings to kill Ramsay, it’s hard to view this as a positive result for Ramsay if he was the author. 5)   The entire letter eloquently parallels Stannis’s burning of Mance at the wall. Ramsay has no reason to know all this or to write a letter that mirrors it.   Next is the letter, I color coded points I would like to reference (obviously):   Bastard, Your false king is dead, bastard. He and all his host were smashed in seven days of battle. I have his magic sword. Tell his red whore.
Your false king’s friends are dead. Their heads upon the walls of Winterfell. Come see them, bastard. Your false king lied, and so did you. You told the world you burned the King-Beyond-the-Wall. Instead you sent him to Winterfell to steal my bride from me.
I will have my bride back. If you want Mance Rayder back, come and get him. I have him in a cage for all the north to see, proof of your lies. The cage is cold, but I have made him a warm cloak from the skins of the six whores who came with him to Winterfell.
I want my bride back. I want the false king’s queen. I want his daughter and his red witch. I want his wildling princess.
I want his little prince, the wildling babe. And I want my Reek. Send them to me, bastard, and I will not trouble you or your black crows. Keep them from me, and I will cut out your bastard’s heart and eat it.
Ramsay Bolton,
Trueborn Lord of Winterfell.   So, let’s dive into the text that I have color coded. I will go in order that the color appears. I’m still figuring out the best way to format, so this might be a mistake but I’m going to put quotes from the other parts of the novels in blue and quotes from the PL in red. Please do not confuse this with the Red and Blue I used in the analysis. I ran out of colors. Much of this analysis is showing that the language used in the letter is very similar to the language Mance uses throughout the series. Language that is not used in many other places in the books. False King When you do a search for “False king” you find that it really is not used often at all (similar to most of mance’s language I will be pointing out). Every time it is either spoken by stannis/ mel, or spoken about Stannis. It is the term Mel uses when burning “Mance” at the wall and again when she is speaking with JS and “RS” before he leaves for the fArya rescue mission. The entire PL mirrors Stannis burning “mance” at the wall. I highly recommend reading “The epistolary Epilogue”  section 7 by Bran Vras for a more in depth comparison of Mance’s burning at the wall and the PL.  Mance is now turning the story around while keeping all the same elements (minus the horn, which may be significant). Stannis told everyone at the wall Mance was dead. Now Mance is telling everyone at the wall that Stannis is dead, using the same “false king’ nomenclature. Both cases are a lie, and instead are acts of manipulation. This is pretty poetic of the author (grrm and PL author). I think Mance would be the only one who would be poetic enough to do this and also have motive to. It’s kind of like, you called me a false king and told everyone I was dead, now I’m going to do the same in a way that also advances my schemes.   Author’s use of the word Bastard. When Mance accepts Jon as a NW deserter, the reason Jon gives for deserting is his Bastard status. Mance knows this a sore spot for Jon and is reminding him of it in the hopes it will encourage him to desert and travel to WF. “And you, Jon Snow?” “You say you were at Winterfell, the night my father feasted King Robert.”…”Then you saw us all.”…”And did you see where I was seated, Mance?” He leaned forwards. “Did you see where they put the bastard?” We also have some dialogue of Mance speaking to JS when glamored as Rattleshirt that is very similar to the PL. Notice the statements of fact or a demand followed by the word bastard. “I’ll range for you, bastard,” Rattleshirt declared. “I’ll give you sage counsel or sing you pretty songs, as you prefer. I’ll even fight for you. Just don’t ask me to wear your cloak.” And “Not me. I'm done with those bloody fools.” Rattleshirt tapped the ruby on his wrist. “Ask your red witch, bastard.” To compare Mance’s words: “I’ll range for you, bastard.” “Ask your red witch, bastard.” Pink Letter words:  “Your false king is dead, bastard”   “Come see them, bastard.”  “Send them to me, bastard,”   Red and Black Only two colors are mentioned in the letter Red and Black. These are Targ colors yes, but also Mance’s colors. His cloak is black with red from the silk from asshai. The red mentioned in the letter is Mel’s red, which also is a red from asshai. The black is from NW’s black cloaks, the same black that Mance’s cloak is. These colors support Mance as the author.   Use of the word whore. Other’s have put a lot of analysis into this, I wish I could find some of the posts I’m thinking of. Ramsay never uses the word “whore” throughout the books, in fact it seems he employs quite the opposite tactic. He refers to horrible gruesome things he does while using language that dances around it’s vulgarity. Instead, Theon seems to be the character that uses the term whore a lot. I have to wonder if the washerwomen/mance got information about Ramsay from Theon. By getting it from a secondary source, the info was biased by theon and the words he uses. This would explain why we see hints of Theon’s language in the text, when the author is trying to sound like Ramsay.   The only name used. This whole letter is a puzzle for the reader to figure out. The puzzle is “who wrote me” not “what parts of me are true”. The proof is in the fact that who wrote the pink letter is still one of the biggest mysteries discussed on the forums. No one is still having a, “what’s true in the PL” discussion. Sure they exist, but not nearly as many as the “who wrote the PL” threads. Knowing it’s a mystery to figure out who wrote it, it is significant the author only chose to use on real name in the letter. This name is “Mance Rayder”. He also happens to be one of the prime suspects for who wrote the PL. It makes no sense for GRRM to point out this name if he is not the author. Instead it makes perfect sense as a wink from GRRM. The answer to our riddle is staring us in the face.   Mance’s language “He burned the man he had to burn, for all the world to see.”-Mance as RS “I have him in a cage for all the north to see.”- PL author It’s not the first time Mance has changed a word to North, i.e. Dornishmans wife.   Ramsay’s language overheard by Mance If Mance is posing as Ramsay, it only makes sense to repeat the threat he’s heard Ramsay make.  "What man?" Ramsay demanded. "Give me his name. Point him out to me, boy, and I will make you a cloak of his skin." –Ramsay says after LW murder, while Mance is in the hall. “I have made him a warm cloak from the skins of the six whores who came with him to Winterfell.”-PL author   Mance’s Language “Red witch” is hardly ever used in the books. I think it’s significant Mance uses it in a statement so similar to these two statements in the PL. “Ask your red witch, bastard.”-Mance as RS “I want his daughter and his red witch.”-PL author “Tell his red whore.”-PL author   Mance’s language As many have pointed out, Black Crows is used exclusively by the wildlings. The fact the Jon Snow find the term “crow” unusual enough to bring up to Master Aemon shows that even the more general term crow is not common in the north. Therefore a more specific term, black crow, is going to be even more exclusive. No one except Mance has any reason to use the word. Mance’s only “reason” is that he either did it unintentionally or that he did it to reveal his identity to one of the readers of the letter. The term “black crow” is used 12 times in the series so far including the letter. Here are some of them: “He can call himself King-beyond-the-Wall all he likes, but he’s still just another old black crow who flew down from the Shadow Tower.” -Osha “Brave black crow,” she mocked. “Well, long before he was king over the free folk, Bael was a great raider.” -Ygritte “Lord Brandon had no other children. At his behest, the black crows flew forth from their castles in the hundreds, but nowhere could they find any sign o’ Bael or this maid.” -Ygritte “Let him die,” insisted the Lord of Bones. “The black crow is a tricksy bird. I trust him not.” -Rattleshirt “The black crow is a tricksy bird, that’s so... but I was a crow when you were no bigger than the babe in Dalla’s belly, Jon Snow. So take care not to play tricksy with me.” -Mance So we have Osha talking about Mance Ygritte talking about Bael the Bard twice (which Mance is inspired by and recreating with his infiltration of WF as a bard), and black crows being referred to as “tricksy birds” by both Mance, and RS whom Mance later assumes the identity of. Nearly half of the times we see the term it is directly related to Mance, Bael the Bard, and the trickery of NW brothers. I’ve found all arguments for why Ramsay or Stannis would use the term to be pretty thin so if you have a good one please let me know!   Mance’s language “Styr scowled. “His heart may still be black.” “Then cut it out.” Mance turned to Rattleshirt.”-Mance “Keep them from me, and I will cut out your bastard’s heart and eat it.” – PL author The threat to cut out a heart is not used that often. The fact that Mance is one of the five or six people who says it further supports him being the author.   Opportunity: I would like to state I do believe Mance’s ploy (at least part) was to bring Rowan with him to the Umbers to make an alliance. I believe Rowan is Mor’s daughter and that Mance and the umbers are now colluding. For anyone who disagrees, I would suggest first revisiting the chapter in which Stannis gives Rattleshirt to Jon and then allows him to stay in the war council. Mance, as RS, hears everything he needs to to know that Mors is willing to negotiate and hates wildings because they stole his daughter.   The Night’s Watch takes no part, Jon thought, but another voice within him said, Words are not swords. “The elder of the Greatjon’s uncles. Crowfood, they call him. A crow once took him for dead and pecked out his eye. He caught the bird in his fist and bit its head off. When Mors was young he was a fearsome fighter. His sons died on the Trident, his wife in childbed. His only daughter was carried off by wildlings thirty years ago.” Later, Mance requests six spearwives from molestown for a certain ploy he has in mind. The wildling turned to Melisandre. "I will need horses. Half a dozen good ones. And this is nothing I can do alone. Some of the spearwives penned up at Mole's Town should serve. Women would be best for this. The girl's more like to trust them, and they will help me carry off a certain ploy I have in mind." "What is he talking about?" Lord Snow asked her. "Your sister." Melisandre put her hand on his arm. "You cannot help her, but he can." And “Young ones, and pretty,” Mance had said. The unburnt king supplied some names, and Dolorous Edd had done the rest, smuggling them from Mole’s Town. Of the washerwomen, only Holly is described as attractive, which means Mance was lying about the criteria he used when hand picking these women. Mel assumes the ploy is rescuing arya. I argue that at least part of the ploy is going to umber lands with the Umber’s daughter, Rowan to form an alliance.  She was one of the singer’s washerwomen, the tall skinny one, too lean and leathery to be called pretty … Hers [hands] were bare, long-fingered, rough, with nails chewed to the quick. “You never asked my name. It’s Rowan.” Umbers are described as leathery elsewhere. Rowan gave him a hard look. “You have no right to mouth Lord Eddard’s words. Not you. Not ever. After what you did Why would a normal wildling know the Stark words or care? Rowan grabbed him by the throat and shoved him back against the barracks wall, her face an inch from his. “Say it again and I will rip your lying tongue out, kinslayer.” Only Mors and the hooded man call Theon a kinslayer. Rowan calling Theon kinslayer supports her being an Umber, and having recently spoken with Mors. “The snow will hide us. Are you deaf? Bolton is sending forth his swords. We have to reach King Stannis before they do.” Again, makes no sense for a normal wildling to refer to stannis as “King Stannis”. Rowan spending a lot of her life in Westeros would explain this. So, based on this evidence I do believe Rowan is an Umber. I believe this is part of Mance’s ploy and that he has made an alliance with the umbers. The coordinated horn blowing outside WF is further proof. As is Mor’s finding fArya and Theon immediately, and recognizing them both.  I am still uncertain whether Stannis is aware of this collaboration. I’m leaning toward him not knowing. If Mance’s skull was the price of Mor’s allegiance, I don’t think he’d be too happy about Mance showing up at his doorstep. It shows Stannis can’t be trusted. ““Half of them, and only if I meet this Crowfood’s price,” said Stannis, in an irritated tone. “He wants Mance Rayder’s skull for a drinking cup” So with Mance collaborating with the umbers, Whoresbane could be the person who sent the letter for Mance with knowledge he acquired at the citadel.   I also believe Mance could have easily communicated a plan with Val before leaving CB. Val seems to have info she could only acquire from Mance, “His milk name. I had to call him something. See that he stays safe and warm. For his mother’s sake, and mine. And keep him away from the red woman. She knows who he is. She sees things in her fires.”
Arya, he thought, hoping it was so. “Ashes and cinders.”
“Kings and dragons.” If Val knows this, there is a very good chance it was Mance who told her it. Mance also brags about being able to climb into tower windows. “I could visit you as easily, my lord. Those guards at your door are a bad jape. A man who has climbed the Wall half a hundred times can climb in a window easy enough. But what good would come of killing you? The crows would only choose someone worse.” Mance could easily have told Val he was alive, going to south of the wall, and had plans that involved bringing the wildlings south of the wall. Between his coordination with the umbers and plans he may have already hatched with Val, Mance knew there would be a good chance other wildlings had came to the wall and were waiting for him to give further instructions.   Motivation: We can never truly know the author’s intent but the actual effect the letter had and who benefits from it is a good place to start. The letter antagonized JS to want to leave CB with a wildling army for WF. This stands to benefit Mance more than anyone. He’s stranded alone in a castle where his known associates just kidnapped the lords daughter. He’s either hiding, a prisoner, dead, or currently in power. No matter what, an army of his loyal supporters is going to help (except the death one). So this outcome is exactly what my theory claims Mance wanted. This outcome is also horrible for Ramsay. He has another enemy now, one with a stronger claim to his castle and one of the few people who can ID fArya. Doesn’t make sense for Ramsay to send this if everything went to plan. The outcome is good for Stannis, so it would support his as the author as well.   Another approach would be to take the letter literally and assume the author was being honest. So we will want to review the demands made, “I want my bride back. I want the false king’s queen. I want his daughter and his red witch. I want his wildling princess.
I want his little prince, the wildling babe. And I want my Reek. “ Though each person holds value for all three potential authors, I believe Mance asking for these people makes the most sense. Ramsay would have little reason to know about val or the baby. I get Mance would be tortured if caught but as badass as he is, I doubt he’s going give up val and the baby. Ramsay doesn’t even know to ask about them. So whether we look at the effect the letter caused or the demands stated in the letter, both point to Mance being the author.   Conclusion: A large amount of the language is specific to Mance. By only using Mance’s real name and only using the colors red and black, GRRM is giving us a clue who the author is. The fact that the entire letter is a reversal of the “Mance” execution at the wall is a further hint. Mance has the means to write the letter and stands to benefit the most from its outcome. The theory that Mance wrote the PL is far more supported by the text than any competing theory.