Feb 19, 6:03pm
Maybe the Mouth went to Dain. The messenger is described vaguely enough that it could have been him; he's not even identified as wearing black, just showing up at night, which anyone can do. The things that makes me think it's a Nazgul is the hissing he made (though anyone can hiss) and that Sauron trusted only the Nazgul to recover the Ring. But Gloin also reports Dain saying the message came under a "fair cloak," and no one (the Gaffer, Farmer Maggot, etc) who meets the Nazgul in the Shire or Bree ever thinks there's anything fair about them, so the hints point in both directions.
‘Then about a year ago a messenger came to Dáin, but not from Moria – from Mordor: a horseman in the night, who called Dáin to his gate. The Lord Sauron the Great, so he said, wished for our friendship. Rings he would give for it, such as he gave of old. And he asked urgently concerning hobbits, of what kind they were, and where they dwelt. “For Sauron knows,” said he, “that one of these was known to you on a time.”
‘At this we were greatly troubled, and we gave no answer. And then his fell voice was lowered, and he would have sweetened it if he could. “As a small token only of your friendship Sauron asks this,” he said: “that you should find this thief,” such was his word, “and get from him, willing or no, a little ring, the least of rings, that once he stole. It is but a trifle that Sauron fancies, and an earnest of your good will. Find it, and three rings that the Dwarf-sires possessed of old shall be returned to you, and the realm of Moria shall be yours for ever. Find only news of the thief, whether he still lives and where, and you shall have great reward and lasting friendship from the Lord. Refuse, and things will not seem so well. Do you refuse?”
‘At that his breath came like the hiss of snakes, and all who stood by shuddered, but Dáin said: “I say neither yea nor nay. I must consider this message and what it means under its fair cloak.”
‘“Consider well, but not too long,” said he.
‘“The time of my thought is my own to spend,” answered Dáin.
‘“For the present,” said he, and rode into the darkness.
‘Heavy have the hearts of our chieftains been since that night. We needed not the fell voice of the messenger to warn us that his words held both menace and deceit; for we knew already that the power that has re-entered Mordor has not changed, and ever it betrayed us of old. Twice the messenger has returned, and has gone unanswered.