Getting ready to run a heavily modified Witchfire Trilogy and I've come up with some stats for the iconic blade.
Witchfire (Overwhelming aura of evil, strong aura of necromancy)
This +2 Greatsword deals an additional 2d6 points of negative energy damage against living targets, and bestows a negative level (no save). The Witchfire's wielder heals 5 hit points whenever the blade bestows a negative level. These hit points are converted into temporary hit points if the wielder is already at full hit points. The wielder can have up to 50 temporary hit points, but they fade at a rate of 5 per 10 minutes.
The Witchfire has an aura of desecration which will bring all kinds of dead things to shambling unlife all around it. This aura extends in a 1 mile radius around the blade. Any creature slain within this aura is raised as a zombie under the control of the Witchfire's wielder 1d4 rounds later. Those creatures in the area which were already dead are likewise raised by this aura, though typically as skeletons. The wielder of the Witchfire also gains control (no save) over all undead of 4 HD or less within the aura. The Witchfire's wielder can cast command undead at will (DC 24) to gain control over more powerful undead.
There is no limit to the number HD which can be raised by Witchfire's aura, though undead which fall outside of its radius fall dormant. If no one wields the blade, the undead will slowly converge on the Witchfire’s location. They may attack anyone who gets in the way.
Each round that an arcane spellcaster of less than 10th level attempts to wield the Witchfire, he suffers a negative level.
The soul of an arcane spellcaster slain by the Witchfire is drawn within the blade, as per soul bind. Whenever this occurs, the wielder of the blade regains an arcane spell slot of each spell level she is capable of casting and receives +2 bonus to caster level for 1 hour.
Souls bound within the blade can be consumed to add metamagic to spells that the wielder casts. This is done spontaneously with no need for further preperation. Alternatively, these souls may be consumed to channel negative energy (2d6 negative energy per soul consumed). The wielder of this blade is considered an undead whenever she channels negative energy. The Witchfire can hold up to 20 souls at one time.
Last Paragraph - Clarification:
Souls bound within the blade can be consumed to add metamagic to spells that the wielder casts. To add a metamagic feat to a spell, a number of souls equal to the level adjustment must be consumed. This is done spontaneously with no need for further preperation. Alternatively, these souls may be used to channel negative energy (2d6 negative energy per soul consumed, DC = 10 + 1/2 the wielder's HD + her Charisma modifier). The Witchfire's wielder is treated as undead whenever she channels negative energy. The Witchfire can hold up to 20 souls at one time.