Witch
A witch is a character in M2TW that appears in provinces with a high percentage of heretical religious worship. She spreads heresy further wherever she goes. A witch can be destroyed by a priest or an imam, by using his "denounce" ability. If the priest or imam fails, there is a chance that the witch will kill the priest, depending upon her magic stat.
Effects
Witches may appear suddenly in regions that have a high heresy rating. Witches also spread heresy in the regions that they are in. They move around the campaign map, approaching characters. A witch can 'curse' a general, giving him negative traits, and may make the character believe that he has been struck by an unholy affliction. A witch has a better chance at cursing a general if she has a high magic rating.
These traits include:
Flatulent
"Ever since this man's encounter with that horrid pagan crone his stomach has been turning endlessly."
-2 command, -1 authority, -2 morale for troops on the battlefield
Warts
"Not so proudly wearing a cluster of warts on his face, no doubt the work of a vile witch."
-1 command, -1 morale for troops on the battlefield
Weaknesses
Witches, like heretics, can be denounced by priests, imams, or cardinals. They are very vulnerable to great imams and cardinals
If you have a priest which has a low piety rating, then call your assassin! You can assassinate a witch and no one will get angry at you! Since the witch is a rebel and she is hunted by all factions, you can "take care" of her, you might sometimes get a mission from the pope to get her assassinated as well!
Contrast with real-life "witches"
The witches of Total War are nuthing like the witches of historical reality.
In real-life, the people who were called "witches" (during the medieval-to-early-modern time period) were no more likely to be heretics than anyone else,
much less did they convert other people to heresies, nor did their magic actually work, and they rarely identified as "witches".
Rather, they were simply people who practiced some form of ineffectual magic, in some cases only once.
Jesus and his apostels said nuthing about magic, either for it or against it, but nuntheless, meny fanatical christians hate magic and the people who practice it, and one pope made the insane decree that so-called "witchcraft" is a form of heresy, despite the fact that witchcraft had nuthing to do with christianity, and therefore cannot be a christian heresy.