Player Verses Player in Mystwood

Mystwood is, ultimately, the story of the struggle between good and evil. No one who is truly evil can write their name in the “Book of Life”, and thus there are no “evil” player characters in Mystwood. That is not to say there are not mean spirited, intolerant, dishonest or bloodthirsty characters, and not to say that characters may not be temped into evil over the course of their career. Mystwood is a world of harsh realities. A game filled with saints would be boring anyway and is just about impossible to achieve. But whatever their flaws, the player characters are all, ultimately, on the same side. They will certainly quarrel and disagree at times, indeed one would be surprised if a Knight Paladin of Mercy and a Witch Hunter did not, and may even attack or kill each other in certain situations, but there are limits.
“Crossing the Line”. A character who joins the side of evil is said to have “Crossed the Line”. You are free to do this, of course. It is your character after all. However, since the game is centered around the “good” side of the conflict, you can’t continue to play that character after the event in which you “Cross over”. You can ask the Nine to allow you to play the character as a NPC villain, which they may or may not do. Otherwise the character is assumed to have fled far away.
Crossing the Line is defined as actively allying with the forces of evil, Unlife or Chaos against the town. It is allowable (though always dangerous) to have dealings with the powers of evil, to try to achieve a “good” goal, to try to redeem evildoers, or in search of power. However, when you open the gate for the undead, fight on the side of chaos against other players, hand over a vital artifact needed to destroy a vampire, or the like you have “crossed the line”, even if you didn’t get caught. Murdering another player character in cold blood is also “crossing the line”.

You can also cross the line involuntarily by acquiring seven Marks of Chaos. In the unlikely event of a player ascending to noble rank they would also become an NPC, as they would then have lands to attend to and little time for adventuring.
The Guild of Shadows and the Town Guard.
Some players enjoy pitting their wits against other players (they are the best competition, after all), for them Mystwood provides a way to do that without destroying the structure of the game.
The Guild of Shadows and the Town Guard are natural antagonists. The Guild takes the side of the common folk against oppressive lords and masters, stealing, raiding, poaching and the like, and giving a portion of their loot to the poor. In extreme cases the Guild even sanctions assassination. Joining the Guild requires various tests, of course. Guildfolk can’t openly admit their affiliation, there is no “Thief” occupation. Instead they appear to be normal folk.

The Town Guard upholds law and order, and thus seeks to thwart the activities of the Guild, and bring them to account for their crimes. There is an unspoken agreement between the two groups - the Town Guard often knows who the Guildfolk are, but does not take action against them without evidence of a crime, and in exchange the Guild does not engage in direct combat against the Guard. Most punishments handed down (such as ordeals, branding, maiming, flogging, etc.) are survivable - killing a Guard is not, so it is generally better to try to get off in court if caught, or accept the consequences. Naturally, the two groups both work to protect the town, each in their own way, and there is often a level of “professional respect” between the two groups.