So, you're considering playing a villain here on At the Crossroads--that's great! Villains play a huge role in stories to provide the heroes with purpose and to create conflict. However, there are both memorable, well-rendered villains who contribute positively to role-play... and the other sort. This file is here to help you create a villain character who does the former! With this in mind, please consider the following:
Motivation
It has been wisely said that every villain is the hero of their own story. For our purposes, this is the point where we would like all potential villain players to begin. A villain should not be a monster who mindlessly or randomly causes mayhem. Monsters are the sorts of things players emit and usually defeat in a scene or two. What separates a villain from a monster? A villain is an at least somewhat rational person who exhibits clear motivation for their actions. They have purpose and exist for more than merely starting trouble or griefing the heroes. They have goals, likes, dislikes, desires, and all the other elements that make up a plausible character. Make sure that your villain has a motivation more interesting than "I want to kill people!" or possibly "I want to kill the Slayer!" Well, why? What makes this--and them--interesting? Bear in mind that "good" and "evil" may be real forces in the world, but they seldom exist in pure forms. Most characters exhibit some sort of shades of gray.
Validation
A villain should offer validation to the heroes around them while also validating their own existence. If the only purpose for a villain is to be evil (see "Motivation," above) then they aren't likely to have a very reasonably validated existence. If a villain does have plausible motivation, then what is it they're doing for the game? What do they contribute, and how much can they really participate? Villains may have horrible long-term (or even short-term) goals, but they should also have the means to role-play--after all, that's what we're here for! Some, like Wolfram and Hart, hide in plain sight and use the system to shield themselves from harm. Others remain in the shadows and only interact with the heroes through villains, perhaps appearing in some disguise or other for social reasons. Sometimes, the best villain is the one who seems like a friend, perhaps even is to some degree a friend, until the critical moment when their true motivation is revealed.
Perspective
One way to test your villain idea is to try altering the point of view. For instance, in a canon-like situation, if Dean Winchester (a hunter) met Scott McCall (a werewolf), each might easily view the other as a villain while viewing himself as a hero. This partly reflects motivation and even validation, but it also raises the importance of perspective. Consider perspective not only from an In Character perspective but also from an Out Of Character perspective. Considering that the role of a villain on a game like this is not to "win" but to motivate and challenge the heroes, try to see how your villain character comes across. Are they behaving in a way that makes it impossible for heroes to even be around them without trying to stop them? Will they force every scene they enter to become a combat scene or similar? Considering these perspectives may help you to anticipate what may be the most important aspect of a villain of all: impact.
Impact
How is your villain character designed to impact the game? That is, what influence are they having on the role-play of others around them? Calling to mind again the principle that the purpose behind villains on a game like this is to generate and enhance role-play by motivating and challenging the heroes, how is your villain designed to do this? Is your villain able to appear in scenes of any type, or are they limited in when and how they can appear--not necessarily for In Character reasons but for reasons of role-play impact. For example, does the villain behave in a way that makes it impossible for heroes to even be around them without trying to stop them? Will they force every scene they enter to become a combat scene or similar? If [Angel]], Buffy Summers, Dean and Sam Winchester, Scott McCall, Myrtle Snow, and the Charmed Ones are all having coffee and donuts in the front yard at Halliwell Manor and your character, "Nefarisse McDarkh," comes walking by, is the social scene going to be disrupted completely? Always consider the impact your character has on the role-play around them.