So...
Blackrazor: Blackrazor is a minor artifact that functions as an intelligent, +3 greatsword. When it deals a killing blow to any living creature, it immediately grants its bearer a number of positive levels equal to the slain creature's Hit Dice. These positive levels last for 24 hours. Because Blackrazor steals the victim' soul, there is only a 50% chance that a wish, miracle, or true resurrection spell can restore a devoured victim to life. Check once for each destroyed creature. If the check fails, the creature cannot be brought back to life by mortal magic.
If Blackrazor is used to strike an undead creature (or other creature with ties to negative energy, such as a slow shadow or xeg-yi), the sword instead bestows one negative level on the wielder, and grants the target 5 temporary hit points (which expire 24 hours later).
Blackrazor has 120 ft. darkvision and hearing. It speaks Common, Abyssal, Infernal, and Draconic, and can communicate telepathically with its wielder. It has deathwatch continually active, and possesses 10 ranks each in Intimidate and Knowledge (the planes), giving it a +13 modifier with both skills.
Blackrazor is neutral evil with the following ability scores: Int 17, Wis 10, Cha 17, Ego 19. Blackrazor's Ego score improves by 1 for every 3 days it goes "unfed". Blackrazor communicates via telepathy.
