(The following information is not general knowledge in the Mutant Chronicles universe. This is a reference for Heretical character, or those who would have at least Average level in Lore of Mutant Chronicles or Lore of Dark Symmetry. Unless your character has these knowledge areas, you should read no further.)
Stages of Corruption
Corruption can come in many forms, but more specifically this refers to the process of being corrupted into heresy by means other than logic or personal choice. There are many who willfully choose to turn to the Darkness, but such is the nature of the Darkness that there are many who are led astray by the power of the Dark Symmetry rather than any personal choice. Those of stronger convictions and will are better able to resist the artificial urgings of the Dark Symmetry, but those who willfully flirt with temptation will eventually fall.
There are four stages of Corruption that may occur to individuals who are compelled for one reason or another along the line of conversion to the Darkness. These stages do not apply to those who have willfully chosen the Darkness, as they are free to choose their fates ... but those who have willingly chosen Darkness over the Light will find that the Dark Soul will not release them easily, should they try to change their ways.
Being Corrupted
Corruption in the sense described above does not happen casually - It only happens as the result of manifestations of the Dark Symmetry. One way for this to happen is for a Heretic with a Dark Gift such as Soul Wither to use it upon the victim, thus artificially pushing him down the road to Corruption. It's important to note that a "pure" soul cannot all at once be pushed into the fourth level of Corruption. There will be time for the person so affected to seek help, if he truly wants it.
Another way for this to happen is if a person handles, possess or uses a product of Dark Technology. Items of Dark Technology - such as weapons of the Dark Legion - have Corruption Factors. For every day that the person possesses (or uses) the object - the character must make a Resistance Roll of MST vs. the object's Corruption Factor. Failure means that the character goes to the next level of Corruption.
Once someone has reached the first level of Corruption, and does not get treatment, the process will continue even if the victim has no further contact, per se, with the Darkness. Once a month, the character must make another Resistance Roll. Failure means progress to the next Corruption Level.
It is important to note here that Corruption is entirely independent of the moral outlook or spiritual well-being of the person so affected. It is, in essence, a supernatural poison that, once it progresses far enough, kills the victim ... and replaces him with something evil. The GM may opt to give particularly faithful PCs bonuses to resist this, but even a murderer may still technically have a "pure" soul before the Dark Legion gets to him. (After all, even murderers are capable of regret and redemption. A fully Corrupted individual is incapable of regret, except perhaps to shed crocodile tears in an attempt at winning sympathy.)
People who are willful Heretics do not have to worry about Corruption Levels or Corruption Factors, but if a PC appears to be waffling and considering turning away from the path of darkness, the GM may start having him make Corruption rolls if he maintains contact with any Dark Influences. If he won't turn to the Darkness willfully, the Darkness still won't let him off easily.
Degeneration
Mortal man was not meant to wield the corrupting energies of the Darkness, and certainly not in large doses all at once. For characters who acquire Necro-Bionics or Bio-Technological Gifts, there is a very real chance with any given implant that Stigmata may develop, and also Degeneration. The acquisition of many Dark Gifts within a short span of time also carries the risk of Degeneration, as it becomes more than a body can handle.
Exactly what constitutes a "short span of time" or "many Dark Gifts" is not wholly known. It is not something that the cultists speak openly about to each other - let alone anyone on the outside. Degeneration can take many forms, especially depending upon which Dark Apostle one follows. It tends to take the form of hair falling out, skin flaking off, and the body generally taking on an unhealthy appearance, as the victim begins to look less alive, and more like the walking dead. If the victim possesses any Bio-Technological Gifts, they will develop grotesque Stigmata appropriate to their type.
When Degeneration comes, it comes suddenly, and the Corporations and Brotherhood are well-versed in knowing the signs. Once Degeneration sets in, it is very difficult to pass for human (or whatever species) anymore ... especially since it invariably gets worse.
Cultists who suffer from Degeneration are generally known as "Sacristans", and they generally retreat to serve in positions in the Temple of their particular Dark Apostle, since they can no longer walk amongst humankind without significant fear of discovery. Sacristans are both shunned and honored, as they bear the mark of their Dark Apostle ... but are also on a slippery slope to devolving into something far less than human. Sacristans tend to be desperate, violent fighters and servants of their Apostles, as they desperately seek some way to prove themselves worthy for Transfiguration - the only way to escape the ultimate fate of Degenerating into a monster.
Cultists of Ilian don't admit to suffering from any problems with Degeneration, but it's rumored that this might be where Ilian gets the "Children of Ilian", though it's also claimed that they are members of yet another alien species that she has conquered. It is known that her Temple Guards suffer a progressive state of madness as they remain in this reality, and those who have become too maddened to be of much use on the battlefield are put into stasis until such time as they can be used as shock troops, as Templars of the Triangled Wheel.
Cultists of Algeroth who suffer Degeneration eventually succumb to the Black Hunger and become Karnophages (flesh-eating ghouls), or else they become walking dead Kadavers.
Cultists of Semai who suffer Degeneration eventually join the ranks of the Heretic Legionnaires. Of all the possible fates, they look the most human, but their souls have withered away long ago.
Cultists of Muawijhe who suffer Degeneration end up as the pathetic Screaming Legionnaires, or else as flesh-eating Karnophages (virtually identical to those in the service of Algeroth). From time to time, they may take other bizarre forms, as befits the supernatural madness they succumb to.
Cultists of Demonogonis who suffer Degeneration go through the most revolting of transformations of all, eventually joining the diseased ranks of the Blessed Legionnaires, or blobs of flesh and filth known as Pustulants.
