Mistwraith

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Mistwraiths are rare beings that float around the landscape. There are only a few left in existance.
To be a Mistwraith is not to be of a race, or of a type of person or skill. It is an affliction. The being may become one with any type of water (usually mist) and is immortal. However, they cannot ever feel warmth and can never be dry, as their nature prevents them from doing so.
How one becomes a Mistwraith is still unknown, whether it be an ancient curse, or a state of being.
Another Mistwraith ability is to absorb a corpse's bones, and use it for themselves. Like if they find the corpse of a squirrel and ingest it, they can transform into a squirrel. However, they cannot and will not ingest any living creature.
Mistwraiths-mostly from boredom of their eternal life-have been known to make wagers or contracts with mortals. Some kingdoms even boast of a Mistwraith being in their ranks of spies.
Mistwraiths cannot kill a human being. They have been known to kill each other, however.
There is no known way to kill a Mistwraith. This secret is guarded by all of the Mistwraiths, and have been sworn since their creation to never betray this to anyone.