These rules, inspired by Warhammer Fantasy Battles, 4th Edition, may be used for an (anti-)Hero Warrior or Wizard aligned with Chaos, or to generate an NPC enemy.
In the northernmost reaches of the Warhammer World, reality has been split asunder by the flow of magic from the Warp Gate that hovers like a great black disc over the north pole. Though such records have been lost to history, long ago there was a race of powerful reptilian beings known as the Old Slann. These beings ruled an empire that spanned countless worlds, and they ruled over these rules with machines and magic, sailing the distance between the stars in strange ships that passed through a chaotic realm known as the Warp. They passed in and out of
the material realm through openings known as Warp Gates, and the hole at the top of the Warhammer World is one of these gates, though destabilized by an ancient cataclysm.
The Slann did not realize it, but the Warp was very alive with powerful beings who were awakened by these trespasses upon their realm. When the Chaos Gods arose from their slumber, the empire of the Slann fell, and the Warhammer World was cut off from the others. Many races had been transplanted from other worlds by the Slann, for their own unknown purposes, and the Warhammer World became theirs ... but it was not theirs alone.
The destabilizing energies of the Warp flow in through the Warp Gate, flowing over the Warhammer World like invisible winds, forming into small eddies or massive storms that may be unseen by mortal eyes, or accompanied by manifestations of foul weather. The dead stir restless in their graves, strange little imps pop into being in the wilderness, and powerful Wizards grasp at the flows of magic and bend it to their will. This intrusion upon the normal laws of reality varies in its intensity, but is most strong in the Chaos Realms of the north, underneath the Warp Gate. There, the land is saturated with magic, so unstable that living things cannot truly exist there -- not without being hopelessly warped by the magic found there, and swallowed up in its madness.
Magic ebbs and flows in its intensity, and where it is strongest, creatures of the Warp live -- for what is lethal to mortals is life-sustaining to them, and they cannot exist long in the mundane world without Chaotic energies to feed them. When the magic flows stronger, these creatures of Chaos march further south, destroying all that represents order, and spreading death and mayhem. With each victory, the fear of the mortal masses gives them more power, and so the vicious cycle continues, with the cancerous growth of Chaos spreading ever further south.
When in time it has been fought back, the armies of Chaos retreat further north, and the powers of magic ebb as well. Areas once transformed by magic slowly melt away into lifeless, bleak wastelands, and the threat to life and sanity is stemmed -- for a time.
Not all mortals shrink away from the threat of Chaos, however. There are some who willingly cast in their lot with the Chaos Gods -- most often the major four of Khorne, Slaanesh, Nurgle or Tzeentch, but sometimes the lesser known Chaos Powers as well. Most of these are dregs of society -- criminals, madmen, outcasts -- but sometimes they are otherwise heroic men wrongfully accused of horrible crimes, or in some other way forced out into the lifeless wastelands, and given no choice but to either cast their lot with Chaos -- or die.
These mortals -- those who haven't the command of magical powers to serve the Chaos Gods as sorcerers -- are generally known as Chaos Thugs or Chaos Warriors. Many of them do not grasp the full reality of their fate, or simply blind themselves to it as they throw themselves with wild abandon into a murderous frenzy at the behest of their new masters. Others serve the Chaos Gods because of the promise of gifts from their masters in the forms of increased power.
The Chaos Gods are fickle, and more often destroy followers that fail to meet their expectations (or simply because the Chaos Gods feel like some entertainment at the expense of whomever happens to be within reach at the time) than they give boons. However, the promised rewards are great indeed, if somewhat mixed. Those especially favored by the Chaos Gods are granted various mutations that are marks of their devotion, and signs of their progression toward the ultimate state of ascension to become a "Daemon" of a warp, and thus gain immortality.
CHAOS CHAMPION HEROES
However, in a Chaotic campaign (such as the MonsterQuest scenario), such a character might fit in well, or else the Hero could be secretly playing a servant of Chaos who is fitting in with the Heroes for some ulterior purpose. It is entirely possible to play a "reformed" servant of Chaos who has joined the Heroes, but in that case, it is best to just treat the character as a normal Warrior or Wizard who happens to have a more colorful past than most -- for the various boons that the Chaos Gods have given him will most assuredly be taken away if he strays from their path and lives to tell the tale.
THE SECRET ANTI-HERO
The simplest way to handle this is to presume that for whatever reason, the Chaos Champion's patron deity has decided that he should work to fit in with the Heroes, to attain some trusted position in order to hatch some nefarious scheme in the far future that has yet to be revealed to anyone. In other words, the Chaos Champion is free to act in the group just like any other Hero, but he simply needs to be more discreet about his special powers, and if he gets too "blessed" by his patron, it could get increasingly difficult to hide his true leanings.
In this case, the GM should try to insure that the Heroes will not be up against monsters that consist of Chaos forces aligned with this particular patron Chaos God -- Rather, the group will always be going up against this Chaos God's rivals (for there is always a great deal of in-fighting amongst them).
If the player of such a character should ever be so indiscreet as to reveal his true allegiance, please be aware of the possibility of in-fighting within the group, and should he even escape the dungeon, he's likely to be hunted down and burned at the stake once word reaches the next settlement he tries to flee to.
CHAMPIONS OF CHAOS
Each of the four major Chaos Gods confers different benefits (and mixed blessings) to its followers. Accompanying these "blessings" are various mutations, often concealed by armor or cowled robes. The following distinctions apply:
For spells that require an Intelligence test to successfully cast, if he fails that roll, he will immediately suffer 1 Wound for invoking his deity's wrath. (Chaos Magic is dangerous that way.)