A long comment on the Black Razors suggested alternative takes the on Duke of Karameikos.

This is just shooting crap. But I was reading over at the Black Razor about alternative takes Duke Stefan of Karamaikos. There are plenty of interesting ideas, but the one that sparked my interest was the chaos cultist take - and just simply loving any quote from the old chaos books.
The post can be read here and it is recommended that it is read for the background for this post, as well as this post about the Black Baron. This post is pretty much an expanded comment on Jonathan's posts. Also, knowledge of the Warhammer universe is required to make any real sense of my scribbles this fine evening, so confusion are to follow, without it.

I was thinking of two scenarios. The first take is the most D&D game friendly, and it requires no knowledge of Warhammer lore. It is as follows.
Stefan has turned to chaos worship of some kind. The Baron of the Black Eagle have come to know of this, but keep it secret while he amasses his forces for the coming holy war. The Duke have intercepted communications meant for the Thyatian Empire but fear to move openly against the Baron, so close to his ascension to daemonhood, therefore he sent the demihumans such as orks, gnolls, and the like against the Black Eagle Barony, while the Duke himself play benevolent ruler - his people will pay back as sacrifices soon enough.
The Baron have turned tyrant in order to maintain order, and summarily execute anyone acting suspiciously to prevent chaos cults to corrupt the Barony from within, while waiting for aid from the Empire - aid never to come...
"All you have been told is a lie"

The second option with Chaos that sprung to my mind draws heavily on older (ignoring the last years of crap) Warhammer Chaos lore, and will make little sense to anyone not familiar with it - but no one read this blog anyway, so:
The Duke started to worship Slaanesh, the god/goddess of sensation. Any sensation is the purview of She Who Thirst. The whisper of the wind, the faint sent of a flower, the merest hint of a smile in the innocent eyes of a child, and the shine in a dew drop lift you to the heavens and beyond when you've surrendered your soul to Shornal. But then, any sensation - ones had, fate to nothing. You will always need new kinds of sensation to be able to stand existence. Before you know it you'll be blood eagle'ing people while sodomizing them in front of the ones they love simply to witness the pain in their loved ones eyes before they are plucked to adorn you neck in a string. And you must multiply that horror with 1000 to get just a cheap idea of what will be everyday life under the lustful gaze of a deamon Lord of the Prince of Chaos.
Duke Stefan is still relatively normal, though, only having toyed with the Prince of Chaos for a short time. The people doesn't know - yet.
The Traladara people of the conquered region now known as Karamikos has many cults in hiding.
Some, having cultivated their burning hatred for the invaders have accepted the demand from Khorn, the Lord of rage, fury, vengeance, blood, slaughter, honor, and discipline. Kharneth will aid those that slaughter in his name - reason irrelevant. Discipline have kept them hidden and organised. The wait have fueled their rage. Soon...
But some have given up hope, sinking in to misery, sobbingly accepting the hand of Grandfather Nurgle granting them tranquility in the security that they can decent no further, and that all will join them eventually, gladly helping cure their countrymens delusion through spreading the plague lords pleasings.
In the Empire of Thyatian, Tzeentch have been orchestrating the Karamaikan situation, unbeknownst to his three dark brethren. The coming bloodshed will be fueling the warp storm on which the Changer Of The Ways will ride over Mystara; another daemon world claimed by the Lord Of Fate.

In the Black Eagle Barony, Ludwig have known of the Traladaran peoples worship of Khorn and Nurgle for some time, but only recently got to know of his Dukes fall to darkness, now having intensified his purity raids on the Baronys populace as a result, while trying to come up with a plan of salvation.


Imagine the PC's being in Specularum as the blood crazed forces of Khorn approach from the one side, and the plague ridden host Nurgle near from the other. Duke Stefan deciding that only mass sacrifice to the Slaanesh may save his worthless hide, sending his loyal (and fallen) palace guard to torture the townsfolk - the still sane towns guard attempting to stop the travesty while still manning the walls soon to meet the foe outside.
The "evil" Baron riding to the rescue?

THATS THE COMMENT PART.


NOTES TO SELF.
I need to write up the daemons of the Chaos powers, adjusted to fit the level titles of B/X, so Imperial (Warhammer Empire) Captains being 4th level (Hero category in the version of the game I know) and Elector Counts being 9th level (Lord category). This will help gauge the power level of the daemons. A Captain can defeat one Flesh hound or Plague Bearer, but not a Keeper of Secrets - nor can an Elector Count.

Daemons of the olden days to consider:
Daemons of Khorn.
And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers.
Bloodthirster (highly resistant to magic). Bloodtletter (resistant to magic), Flesh Hound (immune to magic).
Slaanesh:
To the pure, all things are pure.
Keaper of Seacrets. Demonette (save against magic every round to strike at these strange creatures), Steeds of Slaanesh (always strike first).
Nurgle:
Blessed are the meek: for they shall inherit the earth.
Great Unclean One (contract Nurgles rot if within ? distance and failing save vs. poison - every round), Plauguebearers (save vs. poison on any hit, or contract Nurgles rot), Nurglings.
Tzeentch:
The Lord will come like a thief in the night.
Lord of Change, Pink and Blue horrors (Pink Horrors turn to two Blue Horrors upon defeat), Flamers of Tzeentch (spew Blue Fire of Tzeentch which turn anyone hit in to a chaos spawn if saves are failed - save vs. dragonbreath, then vs. magic), Discks of Tzeentch, Screamers (blue manta rays that fly, basicly).


Ahh, a worthy project for my excellence.