If anyone is interested in my interpretation of the Blue Prince's plan--this isn't meant to be a final word, or anything, just how I took it when I first read it--
The creature "deluges the land with an inky vomit."
Later, the Blue Prince says that the royal wedding will prevent this--"not a scribe will shed ink to tell of his advent."
In other words, as I took it, the "inky vomit" was reporters writing incessantly about the serpent--rather like news coverage today, when after a week or two of All Tiger Woods All the Time and "exclusive interview with Tiger's dog groomer's assistant's cousin!" one might consider the land to be afflicted.
The royal wedding, though, would be much more newsworthy and the serpent, thus, ignored.
That's how I took it, anyway.