The Third Edition Blackguard is another class rooted in the Evil alignment. As we should know from the Assassin, there’s simply no place for alignment in the setting. That part’s a bit of a wash, but we have other stuff to go on if we’re talking about a general conversion from one system to another. First, let’s look at requirements.

Blackguards need a base attack bonus of six or higher, three melee-combat feats (Power Attack, Cleave, and Improved Sunder), and ranks (but not many) in both the Hide and Religion skills. Additionally, they must make peaceful contact with an Evil outsider who they either personally summoned, or had someone call for them.

Right off the bat, if we’re talking powerful Outsiders, we’re looking at the Spectral state, for its ties to Tartarus, and the Sidereal state for its Unknowable Cosmic Entities. Of course we also have the Empyreal state for its connection to the Powers That Be. Just keep that one in the back of your mind for now.

It should be fairly simple that as a powerful force for capital-e Evil (sometimes called an Anti-Paladin for its resemblance to the Paladin), that the Blackguard should be a champion of sorts, which would put them in one of the three Swords classes: Marshal, Warrior, or Soldier. The question is where they fit, exactly.

Now, unlike the Paladin, the Blackguard’s Fiendish Servant isn’t intended to be used as a mount in combat, so they’re probably not the mobile fortresses represented by the Soldier archetype. Honestly, their ability to Command Undead and project an aura probably puts them squarely into the Marshal archetype.

Whereas the Paladin could alternately be considered a Marshal for his leadership abilities, or a Soldier for his mobility and defensive prowess in combat, the Blackguard is pretty clearly a Marshal, or possibly a Warrior if he were to trade his leadership powers for more straightforward combat powers. (Who needs allies anyway?)

So, coming back to the magic state, what we’re probably looking at is essentially an Empyreal Marshal, for his unabashed connection to, and championing of the malign powers. He’s the other side of the same coin as the Paladin, not so different from the “noble” version of the class to constitute a wholly separate power source.