Caligrosto

Caligrostos were a type of loumara (disembodied demonic spirits) that possessed bladed weapons to fulfill their bloodlust. The sadistic shades compelled their wielders to seek out new victims, a category their current wielders could easily find themselves in.

Description
Caligrostos were inherently invisible creatures whose natural state was that of an unseen, shapeless mass. While possessing a weapon, they couldn't be detected by spells such as see invisibility or locate creature, and spells like detect chaos or detect evil wouldn't unveil their nature as a demon, only their alignment. Under truesight, a weapon possessed by a caligrosto would appear to be seething with coils of lightning-flecked mist.

If a caligrosto-possessed weapon managed to injure anyone capable of using it, the caligrosto could take on a more distinct form. The caligrosto's incorporeal incarnation of its victim was both phantasmal and fiendish, a blurry, indistinct shade with features such as glowing red eyes, bat-like wings, and a forked tail. Regardless of the size of the victim, the caligrosto retained the same general mass.

Personality
Of the known types of loumara demons, caligrostos were thought to be the most sadistic, which given the vile delights the other loumara engaged in, implied cruelty so strong that perhaps even some demons would be taken aback. The caligrostos were hateful spirits that from the moment of their conception had a deep-seated need for a blade's edge, living for little more than satisfying their primal, remorseless desire- the thrill of cutting and slicing flesh from bone. They could form attachments to particular weapons and would only abandon them in the direst of circumstances, after which they became obsessed with taking them back before enacting wrathful vengeance against the one that forced them to abandon it.

Caligrostos were also treacherous creatures, skilled liars with a penchant for deception. Though capable of being patient and in possession of a self-preservation instinct, their self-restraint was sometimes overpowered by the desire to betray.

Abilities
In addition to the normal immunities of the loumara, caligrostos were resistant to the cold. They could sap the strength of others with their mere touch, allowing them to heal themselves if injured and obtain greater vigor even if already in peak condition.

Possession
Unlike other loumaras, caligrostos were limited to possessing unattended slashing weapons rather than living creatures. Any normal weapon could be possessed at will, but magic weapons naturally resisted possession, and if the loumara failed to enter it then it could never try again. Once they did possess a magic weapon however, they could enter and leave them as easily as any other, although they couldn't move or drain others whilst occupying a blade and were limited to observing the world and communicating telepathically.

Caligrostos could be forced out of their weapons using spells like banishment, dismissal, dispel chaos, and dispel evil, requiring them to overpower an enchanted weapon again to repossess it. Though caligrostos were incorporeal, the weapons they possessed remained solid, and destroying their tools also forced the spirits out and potentially left them stunned.

Caligrostos could infuse the enchanted weapons they inhabited with additional qualities alongside their existing powers. Ordinary caligrostos could infuse the keen quality, while more powerful ones could also add the wounding quality, and the most powerful of them could add the vorpal quality.

Shade
After a striking a valid target, a caligrosto could attempt to fly free from its wielder's grasp (requiring a strong force of will to keep them still) and create a fiendish shade that would receive and wield the weapon. They were uncannily skilled in the use of bladed weapons and were proficient with whatever weapon they were possessing, using their dexterity to wield their weapons with lethal adeptness despite their lack of strength.

While theoretically able to permanently exist in such a way, a new phantom image would be created of the next creature they struck that could wield their weapon. The phantom facsimile had keen insight into how best to attack the creature it was imitating, and had a bizarre link to the original. Caligrostos were immune to mundane weapons and resisted magical ones, but the displaced harm from being sliced unexpectedly affected the one they were copying instead.

Combat
Caligrosto-possessed weapons could be wielded like any other and if the spirit so desired, they could refrain from making a fiendish shade of another creature. They often used their infusing powers to make the weapon they were haunting seem more appealing, thus increasing the likelihood it would be used in combat, and they sometimes even used telepathy to convince others that they were sentient weapons, typically with the intent of stealing another form.

After tasting flesh and blood, they attempted to escape their wielder's grasp so as to personally inflict the bloodshed in phantom form, often trying to convince their "owner" that they were going to use a short but potent version of the dancing weapon quality so as to fly off without resistance. Once they were free, the caligrosto might first help their previous wielder defeat the current threat, or just immediately turn on them the second they escaped.