|This article is about the current version of DF.|
A villain is a catch-all term for all intelligent historical figures with nefarious intent, making use of intrigue to plot more-or-less undercover for a given goal, which may range from rather prosaic (artifact theft, or abstract embezzling) to extremely nefarious indeed (taking over the world with an undead empire). Likewise, the means and NPCs involved may vary accordingly. In the current version, it is not possible for one's adventurer (or adventuring party, more likely) to become a villain (or villainous organization), though they may attempt to expose them.
Villains come in various flavors: some of them are a natural fit for villainy, like demon lords or necromancers, while others can be various rulers or position holders, or even regular historical figures with appropriate personality traits.
Plotters can use their organization and leadership locations, whether that's a monastery or a mercenary compound or their own castle.
Type of plots
For non-supernatural villains, these are corrupt imprisonment, framing, snatching, sabotage and directing wars to their enemies. They also include intentionally corrupting the government of an enemy (rather than targeting based on location or current assets.) Dwarves and others are variously tempted by e.g. the opportunity to embezzle or accept bribes using the power of their positions. If their personality and values aren't up to the challenge, they may eventually fall to temptation and undertake corrupt activities in an ongoing fashion, which will make them a target for both law enforcement and blackmail.
For hostage-taking, they can obtain a ransom (depending on the position and family of the hostage), imprison the hostage for a period, or just murder them if they run out of ideas. If the villain holds a particularly strong grudge and is vengeful and cruel, they might torture and/or sell the hostage (depending on their values and which civilizations are around). One bright side is that personal prisoners have a chance to escape (it is harder to escape from towers, especially those with dungeons), including those taken by night trolls. Corrupt imprisonment and framing are similar to each other, but the first requires the villain to either personally hold or have influence over the leader or law enforcement of a civilization, while the latter involves excellent intrigue skill use against those same position holders as well as the target. If successful, the target (either a grudge or somebody else to be neutralized) will be charged with a crime and receive whatever punishment is due for it, from exile, to imprisonment, or execution. The villains make sure to check the laws first before they attempt to use either of these techniques.
Starting wars, also bleak, involves corrupting leaders, advisors and generals associated to civilizations with which the target civilization is currently at peace. Skilled intrigue here can disturb diplomatic relations, though this is rather abstract. Similarly, sabotage is a bit thin, but if successful, the agent harms the abstract 'account' of either a grudge or the company/guild they are a part of, which does have an effect on them (Buildings aren't actually destroyed on the site map.)
Necromancers may plot to take over the world. Up-and-coming necromancers may raid old battlefields or infiltrate cities for corpses and building up their army, but once the necromancer is feeling powerful enough, they usually attack the outlying villages of a market town, and if the 'snowball' gets big enough, the market town as well, all in the same invasion during a given year.
Mummies store artifacts in tombs, and if worldgen thieves go for them, this can cause disturbances, as in adventure mode. The resulting mummies form a grudge against the thieves, but also generally take up necromantic and villainous ways.
Demons also plot more or less openly to start wars and steal things, although their agents will still be undercover. Demons associated with the sphere of death will be able to raise corpses and practice necromancy.
The current set of corruption techniques are intimidation, asserting rank, blackmail, flattery, exploiting religious sympathies, promising to take revenge on an enemy, and direct bribery. These are used to corrupt position holders variously and to gain new agents. Promises of rewards for greedy and ambitious targets, especially if the villain or intermediate agent has such things to offer (artifacts, positions, or more abstractly, a portion of a site's available tribute for that year), fear (for their life, or a family member), ideological alignment (easy to check with the value system, though factors like loyalty will need to be accounted for), and revenge are all possibilities.
The villain or their agent chooses a technique based on whichever one they think will provide the best outcome, but if an organization has not been penetrated, or the agent isn't good at their job (intrigue, judging intent, etc.), their assessment of which technique will work can be incorrect (by design.) For instance, they might think a bribe is a good idea, but if they are a terrible judge of character and have nobody inside the target's organization, they might not realize that the target is not greedy and not in debt. But if the target were greedy, or in debt, and the agent has an insider and a good judge-intent roll, they will correctly assess bribery as a useful possibility. Generally, the moments of intimidation, flattery and bribery, have unified modifiers based on skill, personality, and the relationship variables (e.g. intimidation is more successful if the target fears the villain already, and flattery works better if the target trusts them) and can be selected more intelligently, with the ability (upcoming in a bit) to expose most of the factors in the decision-making to legends mode.
Villains make use of cutouts/handlers to work with assassins, and don't need to hire assassins and other agents themselves. In the case where a villain or a handler is duty-bound and important, where a journey that might take several days would seem inappropriate, they may send messages more abstractly, over the same period of time. They often make use of criminal organizations and bandit gangs. For villains without brighter ideas, doing some petty crime with a few like-minded individuals is a start, and then these groups can fuse and otherwise associate, with various skimming and tribute and so forth as some of them grow more powerful. This allows the standard anti-bandit/criminal quests to lead into evidence network crawling, as the most successful groups can draw back to a more villainous status (ie they need discovering rather than generating direct quests.) Plots can propagate out into dedicated criminal organizations from the non-criminal position holders (often through intermediaries), and criminal organizations can also expand out into other cities, forming branches much as the merchant companies do, where they then try to muscle out and subordinate local groups.
Necromancers and vampires may use their secrets and their blood respectively to entice people to join their villainous schemes. Grateful and dutiful villains actually follow through and share their power when an asset proves themselves useful, but others never fulfil their promise.