Curse-Gift Leech

This is the essence of a tanar'ri banished to the Prime Material Plane: an eyeless, featureless slug with writhing tendrils at head and tail. It hides as a crimson steel weapon, a +1 dagger, rapier, magical hook or even pistol, waiting for an intelligent creature to pick it up.

Ungrasped, it can move and attack once per round for its weapon form's damage. Bonded, it uses its host's weapon skill and may let the host use a curse-born gift it has absorbed. Once freed, it attacks everyone nearby for two rounds before being gated home automatically; in true form it has two claws at 4d4 each, casts as a 9th-level wizard and is immune to poison, charm, fire, cold and electricity.

Why these fiends were exiled is unknown, but absorbing curse-born gifts lets them build the power to return. A good priest who grabs it feels it wrench away and skitter off (Strength 20). It never takes a host with a heroic spirit, since they would fight for control at its disadvantage, yet a paladin can hold it despite its evil aura.

Grasped, it sinks tendrils into the flesh with no save and vanishes inside the host, emerging as any of its weapon shapes when the host wills, forcing whatever is in that hand to drop. To steal a gift it makes the host stab a fresh corpse through the heart. The host can refuse a demand with a Wisdom check, holding it off for an hour or until the next dispute. It takes only gifts it lacks, and during each theft the host may save vs. spell (-1 per gift absorbed) to expel it. Fifteen thefts within one host kill that host. With two gifts per Hit Die (20+), it can break its banishment.

It touches the world mostly through its host's choices and needs only victims bearing curse-born gifts.