Ramsay wrote the letter. Whether he's writing it under false knowledge, that's what remains to be seen.
Personally, I think he is. I think he has Mance, I think he killed the spearwives, and I think he has Lightbringer. I don't think Stannis is dead or defeated. In fact, my money is on him pulling a reverse-Bolton (you know, the plan Arya enabled in Harrenhall). Perhaps the Manderly's (and Manderly's dressed as Freys) brought in prisoners from the "battle". This would get a goodly amount of men inside WF ready to be set free to take the castle from the inside out and open a gate for the rest of Stannis' forces.
Makes a lot more sense to me than these other crackpot theories.
Assuming that were true, don't you think Ramsay would have a little too much fighting on his hands with Stannis and Manderly's men inside WF to be writing a demanding letter to Jon? Unless Stannis intends to just chill in WF for a while before taking the castle.
Edited by DCS1122, 13 September 2012 - 02:37 PM.