Planar Bestiary
A distinct variety of devil, a taker of bones could almost be confused for a skeleton, though they are merely skeletally gaunt, not undead. With their two terrible stingers and their bony, crown-like crest, this creature demands attention. And that's even before a victim understands what the devil can demand from them.
The taker of bones can plunge a stinger into a target and pull out their bones, which immediately animate as an undead under the taker's control, leaving the victim a boneless pile of flesh.
A taker's victim has only so much time to retrieve their skeleton before they suffocate.
Motive: Collect "fresh" skeletons from the living, make crooked deals
Environment: The Lower Planes, anywhere in the multiverse, in the company of one or two skeletons
Health: 20
Damage Inflicted: Moderate wound (5 points)
Armor: 2
Movement: Short
Modifications: Speed defense as level 4 due to large size; perception as level 7
Combat: The taker attacks twice each round with their stinger.
Every few rounds, the taker can try to bloodlessly pull the skeleton out of the body of a creature they hit with a stinger attack. The victim takes damage normally, but if the victim fails a Might defense task, the victim's skeleton is removed and deposited in an empty space next to the taker. The stolen bones act as an undead skeleton under the taker's command.
The victim of skeletal theft can't take physical actions, or even speak intelligibly. They can attempt another Might defense task each later round. If successful, their skeleton is no longer under the command of the taker of bones. The uncontrolled skeleton then uses its action to return and fuse with the victim. A victim who regains their skeleton is immune to this effect for one day. If the skeleton is destroyed while roaming outside its owner's body, the victim can't regain their bones. A victim that can't retrieve their bones dies within a few minutes from suffocation (they can't properly breathe) unless they are treated with magic able to remove a curse or similar magical intervention.
A taker of bones is immune to fire and poison attacks.
Interaction: A taker of bones doesn't necessarily wade into a new encounter pulling skeletons from strangers (though they may). Instead, they might ask (in one of several common languages, the language of demons, or telepathically) what they can do for a stranger, insisting that they will take their skeleton as a trophy only when the target no longer has any use for it. The word "when" is important in this deal, because a taker of bones would argue that someone has no use for bones when those bones are not inside them. Anyway, that's the fiend's justification, assuming they can provide the target with the service they ask for (or a reasonable facsimile thereof).
Use: Explorers seeking to enter a sealed structure are greeted by a taker of bones, who says they can get them into the structure "for a price."
GM Intrusion: The taker of bones uses a skeleton under their command as an endpoint destination for a magical teleportation effect, no matter how far away the endpoint is, including across planar boundaries.