I mean it's all in the title really.
The tooth fairy is a benevolent creature that gives you gold, and the Bone Fairy is its evil twin that rips off your bones in exchange for gold. DnD is fun :)
Anyways enjoy the monster !
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Bone Fairy
Lore
Whereas people enjoy the benevolent actions of the tooth fairy, most fear it's elder sister, the bone fairy. This fey is malevolent to the core. Whereas the tooth fairy acts of its own accord to give money to children, the bone fairy is offered gold to tear off the limbs of a few unfortunate souls.
History
Once tooth fairies themselves, greed overtook them. Why should they share their gold, their money with anyone else. That thinking engraved itself into them, twisting their very core, altering their powers. They now make humans kneel before them, and offer them more of the precious gold. In exchange, they'll rip and tear without a second thought. Point them to a target, and watch the carnage. Pray you're not next on the list.