Feeding on Souls—Necrocarnate
The necrocarnate from Magic of Incarnum uses the fell power of necrocarnum, souls tortured and twisted into his dark raiment. For every creature he slays, he takes their soul, burning up its energy for his own purposes over the course of the day.
Sound awesome? I certainly think so. Unfortunately, the design on necrocarnate is very poor. It’s a prestige class for the incarnate class, and does just about everything worse than the incarnate himself did. You get various class features late, if you get them at all. Most importantly, you run primarily on essentia (soul-stuff), but necrocarnate does not improve the amount essentia you get at all. Instead of gaining essentia for leveling up, like a normal incarnate, you have to kill things to get essentia. And unless you’re being really cheesy (e.g. pouring boiling oil down an anthill and claiming a “kill” for each ant), it mostly means you’re behind. In other words, your soul-eating is pointless because you’d have more power if you just didn’t.
Enter sirpercival’s necrocarnate revamp. Sirpercival is one of the most prolific and well-regarded homebrewers for 3.5 (and also a really cool guy—plus how often do you get to say you’re playing a class written by an astrophysicist?). This takes the necrocarnum concept—all the cool I mentioned above—and replaces the shoddy design with a better one. A much better one; the sirpercival necrocarnate is a lot of fun. So this is homebrew, i.e. not official material, but it’s a remake of existing fluff, just with new mechanics.
Regardless of whether you use the official or homebrew versions of the necrocarnate, the fact that it requires 10 ranks in skills means you need 7 levels prior to entry. Two levels of incarnate or five levels of totemist (each from Magic of Incarnum) are required to meet the meldshaping requirements, and since necrocarnate advances your meldshaping as it is, it’s probably best to enter single-classed as one or the other.
The incarnate is literally alignment incarnate—it allows you to be chaos incarnate, evil incarnate, good incarnate, or law incarnate. Law is probably the best of them, chaos is definitely the worst of them, but the differences are not that large. I’d generally recommend law or evil for a necrocarnate (if using the official necrocarnate, the fact that necrocarnate requires Necrocarnum Acolyte and most of that feat is wasted on evil meldshapers—who can shape necrocarnum soulmelds without it—is a strong reason to favor law). Incarnates are simply broadly competent: they hit hard and reliably in combat, they have many skills and the ability to get large bonuses to them, and so on.
The totemist is a savage mauler, calling upon the spirits of various beasts to empower him. The totemist is very good at getting a ridiculous number of attacks. Totemist might also be a decent exception to the single-classed thing: a single level of barbarian, for Rage and trading fast movement for pounce via the lion spiritual totem option in Complete Champion, is very nice for a totemist, and Cobalt Rage is a solid feat (don’t bother with the totem rager prestige class, though, even though you qualify).
Incarnum in general
By the way, Magic of Incarnum is kind of notorious—the book is really hard to read and understand. Information is kind of spread out all over the place, and very difficult to keep track of. A quick-and-simple run-down:
People who use incarnum are known as meldshapers and have a meldshaper level akin to a caster level for a spellcaster.
Meldshapers work with soulmelds, which are glowing blue constructs made out of souls. Most meldshapers use available soul-stuff that is spread throughout the universe; necrocarnates steal souls that were previously in use, and twist and torture them into doing what they want.
Soulmelds are shaped, and may also be bound. The distinction between a soulmeld that is merely shaped versus one that is bound is very important. Shaped soulmelds give a minor benefit, usually a moderate bonus to a pair of skills; bound soulmelds can give quite potent benefits.
All soulmelds are shaped or bound to a chakra, and there is one chakra for each magic item body slot. So just like you can wear an item in your cloak slot, you can shape a soulmeld to your shoulders chakra. No two soulmelds can be shaped to the same chakra.
You can shape a soulmeld to any chakra, but to bind it, you must have that chakra open and have a chakra bind available (meldshapers get a certain number of these at a time). Moreover, if the soulmeld is bound, it suppresses any magic item you have in the same slot.
Example: you are wearing a cloak of resistance +1, and then bind the kraken mantle to your shoulders. Since you have bound a soulmeld to your shoulders, you cloak of resistance +1 is turned off, and you lose the +1 resistance bonus to all saves until the kraken mantle becomes unbound.
On the other hand, shaping (but not binding) sphinx claws to your arms chakra does nothing to the gloves of dexterity +2 that you’re wearing.
All soulmelds that you have shaped (or shaped and bound) can have essentia invested in them. Essentia is soulstuff; meldshapers get a certain amount of it based on class level, and necrocarnates can get more by killing things.
The limit on how much essentia can go in any one soulmeld is based on your character level, and generally ranges from 1 to 4, though meldshapers get class features to expand this somewhat (at high level, with all of the relevant class features, the feat, and the item, you can get the maximum capacity of a soulmeld up to 8).
As a swift action, you can completely rearrange where and how much essentia you have in each soulmeld.
That’s pretty much all there is to it. It’s a complicated system to explain and to learn, but it’s actually a rather simple and elegant system to use in practice. I recommend Sinfire Titan’s Incarnum Guide for more useful tips.
Something Else—Thief of Life
The thief of life prestige class from Faiths of Eberron is a strange class for those devoted to the Blood of Vol. While undeniably cool, the 6+Int skill points you get each level might be the most powerful thing the class has. Still, the borrow vigor, steal vitality, and steal immortality class features are thematically appropriate, and borrow vigor and steal immortality can even give you essentia—in what might be the only reference to incarnum outside of Magic of Incarnum in all of 3.5.
I don’t really recommend it, but it is worth mentioning.
Something Literal—Soul Eater
Book of Vile Darkness has the soul eater prestige class. I’m not a big fan of it; it’s definitely powerful, but it leads to a character who basically does the same thing, every time. It’s a powerful thing, but meh.
The soul eater lets you drain energy from targets with a touch—this is represented by giving them a negative level. As you level, you get various bonuses for doing this: bonuses to Strength, Dexterity, Constitution, saving throws and skill checks, and then you get to shapechange into your victim and turn them into a wight under your control.
It’s powerful; probably too powerful. It’s also boring, and as soon as anything shows up with immunity to energy drain (read: all constructs, undead, anyone who can cast death ward, or anyone with a soulfire armor or shield), you get to do nothing.
As a DM, I ban the soul eater because soul eaters are obnoxiously difficult to challenge appropriately—either their target is vulnerable to negative levels, and the soul eater kills them instantly and without really trying, or else the target is immune and the soul eater can’t do anything to them. It makes them boring to play and boring to play with.
As a necrocarnate, an incarnum race—azurin, duskling, rilkan, and skarn—is useful to you for getting that much more essentia. Essentia is really important, and you’ll probably be picking up the Bonus Essentia feat plus some other [Incarnum] feats just to pump it. Getting essentia from your race could mean saving yourself a feat later. The azurin and duskling are far-and-away your best choices.
Azurin are humans with innate incarnum, losing the human bonus skill point for a point of essentia. This is a very good trade, and then you get to keep the human bonus feat. Since a point of essentia is nearly worth a feat to you anyway, this race is like getting two bonus feats.
Dusklings are weird little black-and-blue fey creatures, and they’re very good. Totemists will dislike their Small size somewhat, but for incarnates that’s a good thing. Their other racial features are quite potent.