Okay, it wasn't very anonymous because it was signed "Thelarwen".
Thelarwen... that was the nice undead lady who loved herbs but didn't love alcohol, right? Coalbrow often sent huge packages of herbs to her, ever since she had asked for a few supplies from him some time ago. Sure, the death knight had said that she didn't need any more herbs. Several times. Very firmly. Oh, but surely she didn't mean it and was just being polite, thought Coalbrow, and continued sending his surplus herbs.
Back to the letter.
Thelarwen wrote:Garrshammer Coalbrow,
During an expedition to Crystalsong Forest in Northrend, we encountered a hostile sample of plant-life, which we vanquished with some effort. I suspect, however, that it was not entirely destroyed. I believe that at least some parts of it escaped our attention by burrowing underground. Because this plant was most aggressive towards us, it is in public interest that the investigation should be concluded and the sample either contained or preferably destroyed. I am contacting you as you are the foremost expert in the field of permanent herb disposal.
What followed was a depiction of the encounter's location as well as a detailed description of the plant's apparent properties and abilities.
The dwarf grinned wickedly. A giant herb waiting to be picked! He gathered various herbalism supplies and headed towards Northrend.
With a warcry "HERB!!!" Garrshammer Coalbrow charged towards the location where the funky flower was last seen.
(Fade to black.)
((Weed)whacking noises.)
(Terrible crunching and martial-arts-flowerpicking noises.)
(Mad cackling.)