I am the Mouth of Sauron.

[ninja91]

Well, I think that he may have a higher rank than the Witch King because he is the lieutenant of Barad-Dur itself. Is that not a rank higher than general of the Morgul-host? Even that is one of the foremost positions in the service of Sauron, although I think that Sauron's personal mouth is somewhat of a higher rank, although that does not mean that it's owner is more powerful than any other.

The following, courtesy of tuckborough.net, helps to explain why the Mouth might be indeed very powerful in the hand of sorcery.

"The Mouth of Sauron was of the race of Black Numenoreans - Men who were corrupted by Sauron in the Second Age. It is said that the Mouth of Sauron "entered the service of the Dark Tower when it first rose again" (RotK, p. 164), but there is some question as to what this means.

Some say this refers to Sauron's return to Barad-dur in 3320 of the Second Age after the fall of Numenor. This would mean that the Mouth of Sauron was over 3,000 years old at the time of the War of the Ring, and that he had somehow prolonged his life by unnatural means."

"Unnatural means" I think refers to sorcery, of course, possibly as a gift from Sauron himself.

tuckborough.net's explanation goes further.

"The Mouth of Sauron was cruel and cunning. He learned sorcery from Sauron and he became familiar with the Dark Lord's mind. He rose through the ranks and became one of Sauron's most trusted servants. If Sauron had won the War of the Ring, the Mouth of Sauron would have been given Isengard and from there he would have subjugated Gondor and Rohan as part of Sauron's domain."

This definitely shows how high and powerful the Mouth really was.