The Master, initially a scary black clad dude you might chance glimpse through a communication mirror used by one of his Agents as they plot the occupation of the Sind, and we eventually discover he is some 'Priest' to a Religion where Lies are holy. He is also surrounded by Diviners. That should be a big clue as to what is realy going on.
The Mystaran Setting is Drowning in Protoindoeuropean links. Hule is Protoindoeuropean for Forest. So the black clad one is also 'Master of the Forest'.
The Master of the Forest
We know he is at the centre of an information network because he uses information to make his lies believable. If you are going to lie to the populace then your lies will need to be backed up with outcomes. We are told his immortal patron is Loki but there is another Immortal trickster (probably Loki as well...he's that kind of Immortal). This particular immortal is patron of the Araena civilization in forests in western region of the Savage Coast. A shape-changing Spider race whose greatest sat at the heart of a forest and an information network. Information is an incredible thing. With a communication network which thanks to a few Mirrors of sending allow strategic manipulation of assets in the field means the Master can pretty much inform one orc chieftan that he controls many by telling chief Boak to converge on the village of Pramyama where he will be met by other forces and then directing others to act together they can capture the Village. Employing diviners (any handful of apprentice magicusers with crystal balls) the Master can control, manipulate, and direct assets as desired.
Chief Boak refusing your orders? Instruct chief Thonk of the Hill Giants to converge on Boak's orcs and kill him for his betrayal and lead them into the village of Pramyama to capture it. The Master is mighty indeed.
The Biggest Lies Pay Big
As some low powered Araena backed up by a bunch of Araena Diviners with crystal balls passing himself off as a BBEG boogeyman the Power of the Master is based on the number of people who believe his lies then convincing everyone that you are responsible for the Asteroid that smashed its way through the skyshield when it is simply an event in motion for thousands, hundreds of thousands, or millions of years.
'The Diviners' or rather the Araena at the centre of a Web has been watching this one coming for a while and informing everyone that you have summoned up a meteor to smite them for failing to stay invaded, while laughed at by everyone as the ramblings of that mad dog at the head of an army of Desert Nomads is soon believed to be a scary dude when a meteor comes through the sky shield and lays waste to two nations.
At the end of the day even the Emperor of Thyatis will be thinking 'Why don't we have one of those Meteor things?'
The Master of the Desert Nomads
The Master of the Hule is a black clad dude with an Information Network...yet the Master of the Desert Nomads is just some crazy Priest guided by the voice of his Immortal. He could very well be some 'Actor' being used by Araenas in control of the Hule to direct their efforts in the Sind.
Other Trickster BBEGs
You dont think this works? Exhibit A: The Mandarin in the Ironman 3 film is responsible for a campaign of Bombings across the USA...but what if these explosions are coincidence?
What if the Mandarin is just some Actor employed to instill fear in the populace and draw the efforts of Authorities away from the real Mandarin?
Its recommended you take a good look at the D&D adventures X4, X5, X10, and the Wrath of the Immortals boxed