Re: Villainous campaigns and player characters?
Villain campaigns should be considered very careful. Why would multiple villains gang up as one? What's their incentive to work together? Just how evil ARE they?
I've played in an evil campaign where the players were all evil in nature, but only because of how others labeled them. For instance, a necromancer who doesn't want to kill living people, but instead wants to protect the undead from the living. He sees the undead as persecuted and despises humans that seek to kill undead. Taking them under his wing, he sees himself as a hero to those who would otherwise be hunted like animals.
Another player in the campaign was an assassin. He had the motto "It isn't my job to know why someone has a bounty, it's my job to collect it." As you can tell, he didn't care who had a bounty, good or evil. If someone had a high enough bounty, he'd make an attempt to assassinate them, no questions asked.
Those are just a couple of examples of evil without the vile attitude of truly villainous beings. This is a great way to do evil campaigns, because they still see themselves as 'doing what they consider the right thing', even if they're evil in the eyes of the majority.
Now if you want a truly vile villainous campaign, you need to find some common goal they would all want to accomplish. True strength, infinite wealth/renown, unending authority. Determine their desires, and play on them as a group. Bind them in ways that they bind themselves to each other. Most villain campaigns end with the players fighting over something, but the truth is they're just not seeing something as mutually beneficial. A good GM will seek ways to make rewards for everyone, without making the party over powered. Instead of big magical mcguffins, smaller but more numerous magical mcguffins so everyone gets something, and they can work out who benefits most from what. The rogue would do best with the elven slippers, the warrior could benefit the most from that belt of giant strength +2, and that +1 bow would do well on the ranger. Nothing super powerful, but all making tiny benefits to the party as a whole.
Finally my favorite villain campaign, the almost-no-combat intrigue game. This one is the hardest to pull off as you need to constantly have new NPCs to interact with, and the party all need to agree that combat is a last option. This is good for parties who have little combat potential, but great dialog/non-combat skills. Good for parties without warrior types, like a Rogue, a Necromancer, and a skill-monkey of some sort, this type of game also works well as a sandbox. Make a town governed by an evil entity, and players could try to take over the town by winning over votes, or they could scam their way through wealth without becoming well known at all. This is good for RPing too because it focuses more on the interactions between players over just constantly rolling dice.
Those are some examples to make a villain campaign work well.