There are two prestige classes in the d20 SRD that are not intended for use by the players; I've already covered one of them (see Nil Mortifi Sine Lucre) but the most infamous villainous prestige class, I think, is the blackguard. Assassins have a pretty narrow focus; at the end of the day their job is to kill people. The blackguard is much more versatile; if there's any Big Evil Thing™ going, chances are he'll want a piece of the action.
We'll assume for the moment that you've read the prestige class description and are thinking about including a blackguard or two in your campaign. Good for you! An easily identifiable supervillain can make a good focus for an adventure.
Most dictionaries define a blackguard as a contemptible or unprincipled person.1 Easy enough to understand; in short, the blackguard should be everything the PCs aren't. While the PCs are an active force of good, or at least have been forced into doing good, the blackguard is actively working to further the cause of evil. They are guided by fiends or other evil outsiders, serve dark gods, have truck with the undead and seek to corrupt or destroy anything that is virtuous. Let's not make any mistake here; they're not just warriors who are a bit sinister and therefore cool.
In this article, I'm going to look at the role played by a blackguard in a campaign and take you through some of the different 'flavours' of blackguard, describing how members of other classes acquire blackguard levels. I'll suggest some feats for them to take, and, as I did before with the assassins, look at the three alignments a blackguard can take and illustrate how their different approaches shape their methods.
Where do they fit in?
While blackguards can and should differ greatly between each other, they have certain things in common. When playing a blackguard -- and it is playing, since they're NPCs -- it's your job as a DM to bring 'em to life -- consider the following points.
It was their decision.
The blackguard made a choice; he was not forced into becoming evil. He may have been tempted, certainly; there may have been threats, but at the end of the day he had a choice, and he willingly chose corruption. This might well sound a bit medieval or cliché. It is. It's meant to be. Blackguards, like paladins are deliberately exaggerated versions of ideals. They renounced such ideas as justice, loyalty and mercy, considering such virtues to be for weaklings; in their place they have chosen iniquity, treachery and cruelty.
They have friends in low places.
The SRD lists the following requirement: The character must have made peaceful contact with an evil outsider who was summoned by him or someone else.
Put simply, the prospective blackguard has to seek out a fiend to sponsor him; the way in which this can be accomplished varies; a simple summon monster spell will suffice, although the spell planar ally and its variants is used more often. This spell calls an outsider to the material plane, entitles the caster to demand a service of it, and offer a service in return. Calling the outsider and compelling it to reveal dark secrets and devoting one's life to evil in return is a classic arrangement.
On top of this, blackguards also attract fiendish servants. Besides just providing assistance or transport, these servants also help to keep blackguards on the path to corruption, egging them on to commit more terrifying acts of brutality.
They know things.
All blackguards have at least two ranks in Knowledge (religion). This doesn't just mean they took their Religious Studies GCSE and passed; it also measures how much they have learned about the tenets of their own dark gods. They have learned certain rituals off by heart, many of which are dist whatever it takes to make things happen according to their design. They fight dirty, and no trick is too low for them.